View source for Union army

{{Short description|Land force that fought for the Union (the North) during the American Civil War}}
{{for|the current active service branch|United States Army}}
{{Use mdy dates|date=October 2018}}
{{Infobox military unit
| image = U.S. flag (35 stars).svg
| caption = [[Flag of the United States]] from 1863 until 1865 (35 states/stars)
| dates = 
| unit_name = Union Army
| country = {{Flag|United States|1865}}
| type = Army
| size = 2,128,948 (700,000 peak)
| command_structure = [[United States Department of War|U.S. Department of War]]
| colors = {{color box|#00008B}} [[Shades of blue#Dark blue|Dark Blue]]
| march = "[[Battle Hymn of the Republic]]"
| battles = {{hidden
|''See battles''
|{{tree list}}
'''[[American Indian Wars]]'''
----
'''[[American Civil War]]'''
*[[Battle of Fort Sumter|Fort Sumter]]
*[[First Battle of Bull Run|First Bull Run]]
*[[Battle of Wilson's Creek|Wilson's Creek]]
*[[Battle of Fort Henry|Forts Henry]] and [[Battle of Fort Donelson|Donelson]]
*[[Peninsula Campaign|Shenandoah]]
*[[Battle of South Mills|South Mills]]
*[[Battle of Richmond|Richmond]]
*[[Battle of Harpers Ferry|Harpers Ferry]]
*[[Battle of Munfordville|Munfordville]]
*[[Battle of Shepherdstown|Shepherdstown]]
*[[Chambersburg Raid]]
*[[Mississippi River campaigns in the American Civil War|Mississippi River]]
*[[Peninsula Campaign|Peninsula]]
*[[Battle of Shiloh|Shiloh]]
*[[Jackson's Valley Campaign]]
*[[Second Battle of Bull Run|Second Bull Run]]
*[[Battle of South Mountain|South Mountain]]
*[[Battle of Antietam|Antietam]]
*[[Battle of Hartsville|Hartsville]]
*[[Battle of Fredericksburg|Fredericksburg]]
*[[Battle of Stones River|Stones River]]
*[[Battle of Chancellorsville|Chancellorsville]]
*[[Battle of Gettysburg|Gettysburg]]
*[[Battle of Champion Hill|Champion Hill]]
*[[Siege of Vicksburg|Vicksburg siege]]
*[[Battle of Corydon|Corydon]]
*[[Battle of Chickamauga|Chickamauga]]
*[[Chattanooga Campaign|Chattanooga]]
*[[Battle of the Wilderness|Wilderness]]
*[[Atlanta Campaign|Atlanta]]
*[[Battle of Spotsylvania Court House|Spotsylvania]]
*[[Second Battle of Sabine Pass|Sabine Pass]]
*[[Battle of New Hope Church|New Hope Church]]
*[[Battle of Pickett's Mill|Pickett's Mill]]
*[[Battle of Cold Harbor|Cold Harbor]]
*[[Battle of Plymouth (1864)|Plymouth]]
*[[Battle of Fort Pillow|Fort Pillow]]
*[[Siege of Petersburg|Petersburg siege]]
*[[Battle of Kennesaw Mountain|Kennesaw Mountain]]
*[[Battle of Jonesborough|Jonesborough]]
*[[Battle of Franklin (1864)|Franklin]]
*[[Battle of Nashville|Nashville]]
----
'''[[Battle of Appomattox Court House|Appomattox Court House]]'''
{{tree list/end}}
|-
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|style=text-align:center;
}}
<!-- Commanders -->| commander1 = President [[Abraham Lincoln]] (1861–1865)<br>President [[Andrew Johnson]] (1865)
| commander1_label = [[Powers of the president of the United States#Commander-in-chief|Commander-in-Chief]]
| commander2 = [[Major general (United States)|MG]] [[Winfield Scott]] (1841–1861)<br>MG [[George B. McClellan]] (1861–1862)<br>MG [[Henry W. Halleck]] (1862–1864)<br>[[General of the Armies|GA]] [[Ulysses S. Grant]] (1864–1869)<ref>After the end of the American Civil War, Grant remained Commanding General of the United States Army until March 4, 1869 when he resigned to be sworn in as eighteenth President of the United States.</ref>
| commander2_label = [[Commanding General of the United States Army|Commanding General]]
| identification_symbol = 
| identification_symbol_label = 
}}
During the [[American Civil War]], the [[United States Army]], the land force that fought to preserve the collective [[Union (American Civil War)|Union]] of the [[U.S. state|states]], was often referred to as the '''Union Army''', the '''Federal Army''', or the '''Northern Army'''.  It proved essential to the restoration and preservation of the [[United States]] as a working, viable republic.

The Union army was made up of the permanent [[Regular Army (United States)|regular army of the United States]], but further fortified, augmented, and strengthened by the many temporary units of dedicated [[United States Volunteers|volunteers]], as well as including those who were drafted in to service as [[Conscription in the United States|conscripts]]. To this end, the Union army fought and ultimately triumphed over the efforts of the [[Confederate States Army]].

Over the course of the war, 2,128,948 men enlisted in the Union army,<ref>{{cite web |url = https://www.civilwar.org/learn/articles/civil-war-facts |title = Civil War Facts|website = American Battlefield Trust|date = August 16, 2011}}</ref> including 178,895, or about 8.4% being [[United States Colored Troops|colored troops]]; 25% of the white men who served were immigrants, and a further 18% were second-generation Americans.<ref name="McPherson, pp.36–37">McPherson, pp.36–37.</ref> 596,670 Union soldiers were killed, wounded or went missing during the war.<ref>{{cite web|url = https://www.civilwar.org/learn/articles/civil-war-casualties |title = Civil War Casualties|website = American Battlefield Trust|date = 15 September 2023}}</ref> The initial call-up in 1861 was for just three months, after which many of these men chose to reenlist for an additional three years.

==Formation==
[[File:Union Private infantry uniform.png|thumb|An illustration of a Union army private infantry uniform]]
[[File:Recruiting poster New York Mounted Rifles.jpg|thumb|Recruiting poster for the [[1st New York Mounted Rifles Regiment]]]]
When the [[American Civil War]] began in April 1861, the U.S. Army included ten regiments of [[infantry]], four of [[artillery]], two of [[cavalry]], two of [[dragoons]], and one of [[mounted rifles]]. The regiments were scattered widely. Of the 197 companies in the U.S. Army, 179 occupied 79 isolated posts in the [[Western United States|West]], and the remaining 18 manned garrisons east of the [[Mississippi River]], mostly along the [[Canada–United States border]] and on the [[East Coast of the United States|U.S. East Coast]]. There were only 16,367 servicemen in the U.S. Army, including 1,108 commissioned officers. Approximately 20% of these officers, most of them [[Southern United States|Southerners]], resigned, choosing to tie their lives and fortunes to the [[Confederate States Army|Confederate army]].<ref>{{Cite book |first=Clayton R. |last=Newell |url=https://history.army.mil/html/books/075/75-1/CMH_Pub_75-1.pdf |archive-url=https://web.archive.org/web/20141023015919/http://www.history.army.mil/html/books/075/75-1/CMH_Pub_75-1.pdf |url-status=dead |archive-date=October 23, 2014 |series=US Army Campaigns of the Civil War|title=The Regular Army before the Civil War, 1845–1860 |pages=50, 52 |publisher=US Army Center of Military History |access-date=26 May 2022}}</ref>

Almost 200 [[United States Military Academy]] graduates who previously left the U.S. Army, including [[Ulysses S. Grant]], [[William Tecumseh Sherman]], and [[Braxton Bragg]], returned to service at the outbreak of the Civil War. This group's loyalties were far more evenly divided. Clayton R. Newell (2014) states, 92 wore Confederate gray and 102 put on the blue of the United States Army.<ref>Newell, p. 52.</ref> Hattaway and Jones (1983), John and David Eicher (2001), and Jennifer M. Murray (2012), state that 99 joined the Confederate army and 114 returned to the Union forces.<ref name=Hattaway9>Hattaway & Jones, pp. 9–10</ref><ref>Eicher, p. 46.</ref><ref>{{Cite book |first=Jennifer M. |last=Murray |url=https://history.army.mil/html/books/075/75-2/CMH_Pub_75-2.pdf |archive-url=https://web.archive.org/web/20121224075449/http://www.history.army.mil/html/books/075/75-2/CMH_Pub_75-2.pdf |url-status=dead |archive-date=December 24, 2012 |series=US Army Campaigns of the Civil War|title=The Civil War Begins, Opening Clashes 1861 |date=2012 |page=9 |publisher=US Army Center of Military History|access-date=26 May 2022}}</ref>

With the [[Confederate States of America|Southern slave states]] declaring secession from the United States, and with a shortage of soldiers in the army, President [[Abraham Lincoln]] [[President Lincoln's 75,000 volunteers|called on the states to raise a force of 75,000 troops]] for three months to put down the Confederate insurrection and defend the national capital in [[Washington, D.C.]] 

Lincoln's call forced the border states to choose sides, and four seceded, making the Confederacy eleven states strong. It turned out that the war itself proved to be much longer and far more extensive in scope and scale than anyone on either side, Union North or Confederate South, expected or even imagined at the outset on the date of July 22, 1861. That was the day that [[United States Congress|Congress]] initially approved and authorized subsidy to allow and support a volunteer army of up to 500,000 troops to the cause.

The call for volunteers initially was easily met by patriotic Northerners, [[Abolitionism in the United States|abolitionists]], and even immigrants who enlisted for a steady income and meals. Over 10,000 [[German Americans]] in [[New York (state)|New York]] and [[Pennsylvania]] immediately responded to Lincoln's call, along with Northern [[French Americans]], who were also quick to volunteer. As more men were needed, however, the number of volunteers fell and both money bounties and forced conscription had to be turned to. Many [[Southern Unionist]]s would also fight for the Union army. An estimated 100,000 white soldiers from states within the Confederacy served in Union army units.<ref>Crofts, Daniel W. [https://digitalcommons.lsu.edu/cgi/viewcontent.cgi?article=3018&context=cwbr CIVIL WAR SESQUICENTENNIAL: Unionism]. ''digitalcommons.lsu.edu''. Retrieved January 29, 2021</ref> Between April 1861 and April 1865, at least 2,128,948 men served in the United States Army, of whom the majority were volunteers.

It is a misconception that the South held an advantage because of the large percentage of professional officers who resigned to join the Confederate army. At the start of the war, there were 824 graduates of the [[United States Military Academy|U.S. Military Academy]] on the active list; of these, 296 resigned or were dismissed, and 184 of those became Confederate officers. Of the approximately 900 West Point graduates who were then civilians, 400 returned to the U.S. Army and 99 to the Confederacy. The ratio of U.S. Army to Confederate professional officers was 642 to 283.<ref name=Hattaway9 /> One of the resigning officers was [[Robert E. Lee]], who had been offered the assignment as commander of a field army to suppress the rebellion. Lee initially disapproved of secession, but refused to bear arms against his native state, [[Virginia in the American Civil War|Virginia]], and resigned to accept the position as commander of the Virginian Confederate forces. Lee eventually became the overall commander of the Confederate army. 

The Confederacy had the advantage of having several military colleges, including [[The Citadel (military college)|The Citadel]] and [[Virginia Military Institute]], but they produced fewer officers. Though officers were able to resign, enlisted soldiers did not have this right. As they usually had to either desert or wait until their enlistment term was over in order to join the Confederate States Army; though few are believed to have done so, their total number is unknown.

==Organization==
[[File:GeorgeMcClellan1861a.jpg|thumb|General [[George B. McClellan]] with staff and dignitaries, including from left to right: Gen. George W. Morell, Lt. Col. A.V. Colburn, Gen. McClellan, Lt. Col. N.B. Sweitzer, [[François d'Orléans, Prince of Joinville|Prince de Joinville]] (son of King [[Louis Philippe I|Louis Philippe of France]]), and the prince's nephew, [[Prince Philippe, Count of Paris|Count de Paris]] (on far right)]]
===Leadership===
[[President of the United States|U.S. President]] [[Abraham Lincoln]] exercised supreme [[command and control]] over the army in his capacity as [[Powers of the president of the United States#Commander-in-chief|commander-in-chief]] of the [[United States Armed Forces]]. Below him was the [[Secretary of War]], who oversaw the administration of the army, and the [[General-in-chief#United States|general-in-chief]], who directed the field operations of the army.  

At the start of the war, [[Simon Cameron]] served as Secretary of War before being replaced in January 1862 by [[Edwin Stanton]].  The role of general-in-chief was filled by several men during the course of the war:<ref name=USAL195>United States Army Logistics, 1775–1992: An Anthology. (1997). United States: Center of Military History, U.S. Army. p. 194-195</ref>
*[[Winfield Scott]]: July 5, 1841{{spaced ndash}}November 1, 1861
*[[George B. McClellan]]: November 1, 1861{{spaced ndash}}March 11, 1862
*[[Henry W. Halleck]]: July 23, 1862{{spaced ndash}}March 9, 1864
*[[Ulysses S. Grant]]: March 9, 1864{{spaced ndash}}March 4, 1869

The gap from March 11 to July 23, 1862, was filled with direct control of the army by President Lincoln and Secretary Stanton, with the help of an unofficial "War Board" that was established on March 17, 1862. The board consisted of [[Ethan A. Hitchcock (general)|Ethan A. Hitchcock]], the chairman, with Department of War bureau chiefs [[Lorenzo Thomas]] (Adjutant General), [[Montgomery C. Meigs (1816–1892)|Montgomery C. Meigs]] (Quartermaster General), [[Joseph G. Totten]] (Chief of Engineers), [[James Wolfe Ripley|James W. Ripley]] (Chief of Ordnance), and [[Joseph P. Taylor]] (Commissary General).<ref>Eicher, pp. 37–38.</ref>

Reporting directly to the Secretary of War were the bureau chiefs or heads of staff departments which made up the [[Department of War]].  These included, at the onset of the war, the [[United States Army Adjutant General's Corps|adjutant general]], [[Office of the Inspector General of the United States Army|inspector general]], [[Paymaster-General of the United States Army|paymaster-general]], [[Judge Advocate General's Corps, United States Army|judge advocate general]], [[chief of engineers]], [[United States Army Corps of Topographical Engineers|chief of topographical engineers]], [[Quartermaster General of the United States Army|quartermaster general]], commissary general of subsistence, [[Chief of Ordnance of the United States Army|chief of ordnance]], and [[Surgeon General of the United States Army|surgeon general]].

After the war started, the position of [[United States Army Provost Marshal General|Provost Marshal General]] was also created.<ref name=USAL195/>  Originally established on September 24, 1862, as an office in the Adjutant General's department under [[Simeon Draper]], it was made an independent department in its own right on May 1, 1863, under [[James B. Fry]].<ref name="Eicher58">Eicher, p. 58</ref>  The [[Signal Corps (United States Army)|Signal Corps]] was created and deployed for the first time, through the leadership of [[Albert J. Myer]].

One drawback to this system was that the authority and responsibilities of the Secretary of War, his [[United States Assistant Secretary of War|Assistant Secretaries]], and the General-in-Chief were not clearly delineated.  Additionally, the efforts of the four "supply" departments (Quartermaster, Subsistence, Ordnance & Medical) were not coordinated with each other, a condition that would last throughout the war.  Although the "War Board" could provide military advice and help coordinate military policy, it was not until the appointment of Ulysses Grant as General-in-Chief was there more than the vaguest coordination of military strategy and logistics.<ref name=USAL195/>

===Major organizations===
The Union army was composed of numerous organizations, which were generally organized geographically.

; [[Union Army Divisions, Departments and Districts|Military division]]
: A collection of Departments reporting to one commander (e.g., [[Military Division of the Mississippi]], [[Middle Military Division]], [[Military Division of the James]]). Military Divisions were similar to the more modern term [[Theater (warfare)|Theater]]; and were modeled close to, though not synonymous with, the existing theaters of war.
; [[Union Army Divisions, Departments and Districts|Department]]
: An organization that covered a defined region, including responsibilities for the Federal installations therein and for the field armies within their borders. Those named for states usually referred to Southern states that had been occupied. It was more common to name departments for rivers (such as [[Department of the Tennessee]], [[Department of the Cumberland]]) or regions ([[Department of the Pacific]], [[Department of New England]], [[Department of the East]], [[Department of the West]], [[Middle Department]]).
; [[Union Army Divisions, Departments and Districts|District]]
: A territorial subdivision of a Department (e.g., District of Cairo, District of East Tennessee). There were also Subdistricts for smaller regions.
; Army
: The fighting force that was usually, but not always, assigned to a District or Department but could operate over wider areas.  An army could contain between one and eight corps, with an average of three.<ref name="Eicher66">Eicher, p. 65-66</ref>  Some of the most prominent armies were:
:*[[Army of the Cumberland]], the army operating primarily in [[Tennessee]], and later [[Georgia (U.S. state)|Georgia]], commanded by [[William S. Rosecrans]] and [[George Henry Thomas]].
:*[[Army of Georgia]], operated in the March to the Sea and the Carolinas commanded by [[Henry W. Slocum]].
:*[[Army of the Gulf]], the army operating in the region bordering the [[Gulf of Mexico]], commanded by [[Benjamin Butler (politician)|Benjamin Butler]], [[Nathaniel P. Banks]], and [[Edward Canby]].
:*[[Army of the James]], the army operating on the [[Virginia Peninsula]], 1864–65, commanded by Benjamin Butler and [[Edward Ord]].
:*[[Army of the Mississippi]], a briefly existing army operating on the Mississippi River, in two incarnations—under [[John Pope (general)|John Pope]] and [[William S. Rosecrans]] in 1862; under [[John A. McClernand]] in 1863.
:*[[Army of the Ohio]], the army operating primarily in [[Kentucky]] and later Tennessee and Georgia, commanded by [[Don Carlos Buell]], [[Ambrose E. Burnside]], [[John G. Foster]], and [[John M. Schofield]].
:*[[Army of the Potomac]], the principal army in the [[Eastern Theater of the American Civil War|Eastern Theater]], commanded by [[George B. McClellan]], Ambrose E. Burnside, [[Joseph Hooker]], and [[George G. Meade]].
:*[[Army of the Shenandoah (Union)|Army of the Shenandoah]], the army operating in the [[Shenandoah Valley]], under [[David Hunter]], [[Philip Sheridan]], and [[Horatio G. Wright]].
:*[[Army of the Tennessee]], the most famous army in the [[Western Theater of the American Civil War|Western Theater]], operating through Kentucky, Tennessee, Mississippi, Georgia, and the [[Carolinas]]; commanded by [[Ulysses S. Grant]], [[William T. Sherman]], [[James B. McPherson]], and [[Oliver O. Howard]].
:*[[Army of Virginia]], the army assembled under [[John Pope (general)|John Pope]] for the [[Northern Virginia Campaign]].

Each of these armies was usually commanded by a [[Major general (United States)|major general]]. Typically, the Department or District commander also had field command of the army of the same name, but some conflicts within the ranks occurred when this was not true, particularly when an army crossed a geographic boundary.

The commanding officer of an army was authorized a number of [[aides-de-camp]] as their personal staff and a general [[Staff (military)|staff]].  The general staff included representatives of the other combat arms, such as a chief of artillery and chief of cavalry (the infantry being typically represented by the commanding officer) and representatives of the staff bureaus and offices.<ref name="Eicher40">Eicher, p. 40</ref>  The staff department officers typically assigned to an army or military department included an assistant adjutant general, a chief quartermaster, a chief commissary of subsistence, an assistant inspector general, an ordnance officer (all with the rank of [[colonel]]) and a medical director.<ref name="newell71">newell & shrader, p. 71</ref>  The actual number of personnel assigned to an army's headquarters could be quite large: at Gettysburg the headquarters of General Meade (excluding engineers, the artillery reserve and the headquarters of each corps) was no less than 3,486 strong.<ref>Griffith, P. (2001). Battle Tactics of the Civil War. United Kingdom: Yale University Press. p. 55</ref>

===Tactical organizations===
The [[military organization]] of the United States Army was based on the traditions developed in Europe, with the [[regiment]] being the basis of recruitment, training and maneuvering. However, for a variety of reasons there could be vast differences in the number of actual soldiers organized even into units of the same type. Changes in how units were structured during the course of the war, contrasts in organizational principals between regular and volunteer units, and even simple misnaming all played a role. Thus for example, comparing two infantry regiments at their full authorized strength one might have twice as many soldiers as the other. Furthermore, even when units were of equivalent size, their actual effectiveness depended greatly on training, leadership, equipment and other factors.<ref name="Eicher66" />
{|class="wikitable" style="display: inline-table;" 
! style="text-align:center; background:#acc;" |Name
! style="text-align:l center; background:#acc;" |Commander
! style="text-align:l center; background:#acc;" |Sub-units
! style="text-align:center; background:#acc;" |Soldiers
! style="text-align:center; background:#acc;" |Notes
|-
|+Union army tactical organizations<ref name="Eicher66"/><ref name="NCMuseum">{{cite web|title=Civil War Army Organization and Rank|url=https://www.ncmuseumofhistory.org/civil-war-army-organization-and-rank|publisher=North Carolina Museum of History|access-date=6 August 2021|archive-date=July 18, 2017|archive-url=https://web.archive.org/web/20170718010330/http://ncmuseumofhistory.org/civil-war-army-organization-and-rank|url-status=dead}}</ref><ref name="McGrath">McGrath, p. 17–20</ref><ref name="Wilson">Wilson, p. 12–15</ref>
|-
|[[Corps#American Civil War|Corps]]
|Major general
|2–6 divisions
|36,000
|Averaged three divisions, included a dedicated artillery brigade after 1863. See also [[Cavalry Corps (Union Army)|Cavalry Corps]].
|-
|[[Divisions of the United States Army#American Civil War|Division]]
|Major general
|2–6 brigades
|12,000
|Averaged three brigades for infantry divisions, two brigades for cavalry. Also included attached [[artillery battery|artillery batteries]] until 1863.
|-
|[[Brigade (United States Army)|Brigade]]
|[[Brigadier general (United States)|Brigadier general]]
|2–12 regiments
|4,000
|Averaged four regiments for both infantry and cavalry.  Artillery brigades consisted of between four and six batteries.
|-
|[[Regiment (United States Army)|Regiment]]
|[[Colonel (United States)|Colonel]]
|10 companies
|1,000
|Actual size would vary as attrition reduced the regiment down to several hundred soldiers or fewer. Artillery regiments consisted of twelve batteries but were purely administrative units.
|-
|[[Battalion (United States Army)|Battalion]]
|[[Major (United States)|Major]]
|Varied
|Varied
|With some exceptions, a battalion may refer to any two or more companies of a regiment or if a regiment consisted of between four and eight companies total.
|-
|[[Company (United States Army)|Company]]
|[[Captain (United States O-3)|Captain]]
|2 platoons
|100
|Cavalry equivalent referred to as a [[troop]]. Artillery equivalent referred to as [[artillery battery|battery]], contain between four and six artillery pieces.
|}

{{Union Army Formations}}

==Personnel==
===Regulars vs. volunteers===
[[File:Currier & Ives - The champions of the Union 1861.jpg|thumb|''The champions of the Union'', an 1861 lithograph by [[Currier and Ives]]]]
During the course of the Civil War, the vast majority of soldiers fighting to preserve the Union were in the [[United States Volunteers|volunteer units]].  The pre-war regular army numbered approximately 16,400 soldiers, but by the end while the Union army had grown to over a million soldiers, the number of regular personnel was still approximately 21,699, of whom several were serving with volunteer forces. Only 62,000 commissions and enlistments in total were issued for the regular army during the war as most new personnel preferred volunteer service.<ref>Eicher, p. 46</ref><ref name="Newell76">Newell & Shrader, p. 76</ref> Due to their pre-war experience, they were considered by many as elite troops and during battles were often kept in reserve in case of emergencies. 

Since before the Civil War, the American public had a generally negative view of the nation's armed forces, attributable to a [[Jeffersonian democracy|Jeffersonian]] ideal which saw [[standing armies]] as a threat to democracy and instead valorized the "[[citizen soldier]]" as being more in keeping with American ideals of equality and [[rugged individualism]].<ref name="Newell3">Newell & Shrader, p. 1-3</ref>  This attitude remained unchanged during the Civil War, and afterwards many would attribute the Union's victory to the volunteers rather than the leadership and staff work provided by the regular army.<ref name="Newell312">Newell & Shrader, p. 308-312</ref>  In return, officers of the regular army despised the militia and saw them as having dubious value.  Commentators such as [[Emory Upton]] would later argue that the reliance on militia for the nation's defense was responsible for prolonging conflicts and making them more expensive in both money and lives spent.<ref name="Newell3"/><ref name="Newell312" />

Despite these attitudes towards the regulars, they would serve as an important foundation around which the Union army was built.  In the disastrous [[First Battle of Bull Run]], it was the regulars who acted as rearguard during the retreat while the volunteers fled, and when George McClellan was put in charge of what became the Army of the Potomac he used regular officers and non-commissioned officers to train the volunteers.<ref>Newell & Shrader, p. 210</ref>  Training the volunteers, especially in regards to critical administrative and logistical matters, remained an important function of the regulars during the war.<ref name="Newell308">Newell & Shrader, p. 306-308</ref>  This was particularly the case with regular army artillery, as they were more widely dispersed than the infantry and cavalry (making them more visible to the volunteers) and were assigned to specific units to train their volunteer counterparts.<ref name="Newell285">Newell & Shrader, p. 283-285</ref>

In battle, the regulars' performance could impress even the most battle-hardened volunteers.<ref name="Newell218">Newell & Shrader, p. 215-218</ref>   At [[The Wheatfield]] during the [[Battle of Gettysburg]], the regulars' fighting skill and orderly retirement under fire drew the admiration of many observers, including [[Prince Philippe, Count of Paris]].  As one volunteer put it, "For two years the U.S. Regulars taught us how to be soldiers [;] in the Wheatfield at Gettysburg, they taught us how to die like soldiers."<ref>Newell & Shrader, p. 235</ref>  The regulars became the standard by which the Volunteers were measured, and to be described as being as good or better than them was considered the highest compliment.<ref>Newell & Shrader, p. 312</ref>

===Officers===
[[File:Washington, District of Columbia. Officers of 3d Regiment Massachusetts Heavy Artillery.jpg|thumb|Officers of the [[3rd Massachusetts Heavy Artillery Regiment]] defending the national capital of [[Washington, D.C.]], in 1865, the final year of the Civil War]]
[[Commissioned officers]] in the Union army could be divided in several categories: [[general officer]]s, including [[lieutenant general]], which was added on March 2, 1864, [[major general]]s and [[brigadier general]]s; [[field officers]] including [[colonel]]s, [[lieutenant colonel]]s and [[Major (rank)|major]]s; and [[Company-grade officer|company officers]] including [[Captain (military rank)|captains]], [[first lieutenant]]s and [[second lieutenant]]s. There was further differentiation between line officers, who were members of the artillery, cavalry or infantry branches, and staff officers, who were part of the various departments and bureaus of the War Department. All line officers outranked staff officers except in cases pertaining to their staff assignment, in which they received their orders from their respective department chiefs.<ref name="Eicher30">Eicher, p. 30</ref> Regular general officers outranked volunteer general officers of the same grade regardless of their date of commission, a feature which could have become a subject of contention.<ref name="Eicher23">Eicher, p. 34</ref> The use of [[Brevet (military)#American Civil War|brevet ranks]] was also a common feature of the Union army.

Officer appointments depended on the commission grade and whether it was in the regular or volunteer forces. The President reserved the right to issue commission for all regular officers and for general officers in the volunteer forces. Volunteer field and company-grade officers could be commissioned by either the president or their respective governor. Company officers were also unique in that they were usually elected by members of their company.<ref name="Eicher30" /> The political appointment and/or election of volunteer officers was part of a long-standing militia tradition and of a [[Spoils system|political patronage system]] common in the United States. While many of these officers were West Point graduates or had prior military experience, others had none, nor was military leadership a primary consideration in such appointments.<ref name="Perryville">Staff Ride Handbook for the Battle of Perryville, 8 October 1862. (2005). Fort Leavenworth, KS: Combat Studies Institute, US Army Command and General Staff College. p. 3–6</ref> Such a policy inevitably resulted in the promotion of inept officers over more able commanders. As the war dragged on and casualties mounted, governors reacted to their constituents' complaints and instead began to issue commissions on the basis of battlefield rather than political competence.<ref>Fisher, E. F. (2001). ''Guardians of the Republic: A History of the Noncommissioned Officer Corps of the U.S. Army''. United Kingdom: Stackpole Books. p. 111</ref>

Officers tended to suffer a higher percentage of battle wounds on account of either the necessity of leading their units into combat and their conspicuousness when accompanied by staff and escorts.<ref name="Eicher61" />

Among memorable field leaders of the army were [[Nathaniel Lyon]] (first Union general to be killed in battle during the war), [[William Rosecrans]], [[George Henry Thomas]], [[William Tecumseh Sherman]], [[Phil Sheridan]], and [[Benjamin Butler (politician)|Benjamin F. Butler]].

;Officer ranks
{| style="border:1px solid #8888aa; background-color:#f7f8ff; padding:5px; font-size:95%; margin: 0px 12px 12px 0px;"
{{Ranks and Insignia of Non NATO Armed Forces/OF/Blank}}
|- style="text-align:center;"
| rowspan=2| '''1861–1864'''<ref>{{cite book |author=Adjutant General's Office |title=Regulations for the Uniform and Dress of the Army of the United States 1861 |date=13 March 1861 |publisher=George W. Bowman, Public Printer |location=Washington |url=http://www.usregulars.com/genorder6.html |access-date=9 December 2022 |archive-url=https://web.archive.org/web/20080215222851/http://www.usregulars.com/genorder6.html |archive-date=15 February 2008 |pages=12–13}}</ref>
| colspan=4 rowspan=2| 
| colspan=2| [[File:US Army O9 (1861).svg|100px]]
| colspan=2| [[File:US Army O8 (1861).svg|100px]]
| colspan=2| [[File:US Army O7 (1861).svg|100px]]
| colspan=2| [[File:US Army O6 (1861).svg|100px]]
| colspan=2| [[File:US Army O5 (1861).svg|100px]]
| colspan=2| [[File:US Army O4 (1861).svg|100px]]
| colspan=2| [[File:US Army O3 (1861).svg|100px]]
| colspan=3| [[File:US Army O2 (1861).svg|100px]]
| colspan=3| [[File:US Army O1 (1861).svg|100px]]
|- style="text-align:center;"
| colspan=2| [[Major general (United States)|Major general]]<br>[[Commanding General of the United States Army#Commanding General of the United States Army|Commanding the Army]]
| colspan=2| [[Major general (United States)|Major general]]
| colspan=2| [[Brigadier general (United States)|Brigadier general]]
| colspan=2| [[Colonel (United States)|Colonel]]
| colspan=2| [[Lieutenant Colonel (United States)|Lieutenant colonel]]
| colspan=2| [[Major (United States)|Major]]
| colspan=2| [[Captain (Union Army)|Captain]]
| colspan=3| [[First lieutenant#United States|First lieutenant]]
| colspan=3| [[Second lieutenant#United States|Second lieutenant]]
|- style="text-align:center;"
| rowspan=2| '''1864–1866'''<ref>{{cite web |last1=Searles |first1=Harry |title=General Orders, No. 87 (U.S. War Department) |url=https://www.americanhistorycentral.com/entries/general-orders-no-87-u-s-war-department/#:~:text=On%20March%203%2C%201864%2C%20the%20U.S.%20War%20Department,on%20the%20same%20day%20the%20order%20was%20issued. |website=americanhistorycentral.com |access-date=26 December 2022}}</ref>
| colspan=4 rowspan=2| 
| colspan=2| [[File:US Army O9 (1861).svg|100px]]
| colspan=2| [[File:US Army O8 (1861).svg|100px]]
| colspan=2| [[File:US Army O7 (1861).svg|100px]]
| colspan=2| [[File:US Army O6 (1861).svg|100px]]
| colspan=2| [[File:US Army O5 (1861).svg|100px]]
| colspan=2| [[File:US Army O4 (1861).svg|100px]]
| colspan=2| [[File:US Army O3 (1861).svg|100px]]
| colspan=3| [[File:US Army O2 (1861).svg|100px]]
| colspan=3| [[File:US Army O1 (1861).svg|100px]]
|- style="text-align:center;"
| colspan=2| [[Lieutenant general (United States)|Lieutenant general]]
| colspan=2| [[Major general (United States)|Major general]]
| colspan=2| [[Brigadier general (United States)|Brigadier general]]
| colspan=2| [[Colonel (United States)|Colonel]]
| colspan=2| [[Lieutenant Colonel (United States)|Lieutenant colonel]]
| colspan=2| [[Major (United States)|Major]]
| colspan=2| [[Captain (Union Army)|Captain]]
| colspan=3| [[First lieutenant#United States|First lieutenant]]
| colspan=3| [[Second lieutenant#United States|Second lieutenant]]
|}
*[[Lieutenant general (United States)|Lieutenant general]]: The rank of lieutenant general did not exist in the Union army for most of the war until February 1864, when an [[Act of Congress]] allowed for its creation. A single lieutenant general was authorized to serve as the commander of all the field armies and geographic departments of the United States, under the direction and at the pleasure of the [[President of the United States|President]]. By law, they were allowed two secretaries and four [[aide-de-camp|aides-de-camp]] with the rank of lieutenant colonel, and a [[Chief of staff#In the United States 2|chief of staff]] with the rank of brigadier general.<ref>Kautz, A. V. (1866). Customs of Service for Officers of the Army: As Derived from Law and Regulations and Practiced in the United States Army. United States: J.B. Lippincott & Company. p. 378–380</ref>
*[[Major general (United States)|Major general]]: Major generals were nominally the commanding officer of a division, although given the lack of higher grades of general officers they were also given command of army corps, field armies and geographic departments. In the event two or more officers of the same grade were present in the same army or department, command was decided by seniority. In an exception to this practice, the president was authorized by law to appoint a junior officer to command over his seniors. A major general was allowed a personal staff of three aides-de-camp. These were personally chosen by the general from among the captains and lieutenants of the army and would accompany him whenever his command changed, being separate from the general staff of the unit he commanded.<ref>Kautz (1866), p. 376–377</ref>
*[[Brigadier general (United States)|Brigadier general]]: A brigadier general was typically in command of a brigade, but like major generals it was not uncommon for them to command larger units. They were responsible for the organization and administration of their command, particularly when operating independently. As with major generals they were also allowed a personal staff of two aides-de-camp of lieutenant grade.<ref>Kautz (1866), p. 375–376</ref>
*[[Colonel (United States)|Colonel]]: A colonel was the commanding officer of a regiment, though they might also be assigned the commanding officer of larger units or expeditions.<ref>Kautz (1866), p. 276–277</ref> They oversaw the recruitment, organization and training of their regiment; conducted parades, reviews and inspections; and managed the administration of the unit, ensuring that soldiers were clothed, fed, armed and paid.<ref>Kautz (1866), p. 278–314</ref>
*[[Lieutenant colonel (United States)|Lieutenant colonel]]: A lieutenant colonel was the senior assistant to their regiment's colonel in carrying out his duties and taking command in his absence. When the regiment was split among several posts, the lieutenant colonel would command a [[Detachment (military)|detachment]] of four companies. Of those duties specific to a lieutenant colonel were taking care of the personal property of deceased officers; act as [[officer of the day]] for a brigade; and conduct regimental [[court martial|courts martial]].<ref>Kautz (1866), p. 275–276</ref>
*[[Major (United States)|Major]]: A major acted as an assistant to their regiment's colonel in carrying out his duties and commanded [[Detachment (military)|detachments]] of two or more companies. The specific duties of a major were also the same as a lieutenant colonel.<ref>Kautz (1866), 265–275</ref>
*[[Captain (United States O-3)|Captain]]: A captain was the commanding officer of a company and saw to its administration. This included selecting (with the colonel's approval) and training non-commissioned officers, issuing punishments and conducting courts martial, and maintaining company [[recordkeeping|records and books]] such as inventories and the [[muster roll]].<ref>Kautz (1866), p. 223–260</ref> They also served as the officer of the day at a regimental camp or small post.<ref>Kautz (1866), p. 260</ref>
*[[Lieutenant#Lieutenant|Lieutenant]]: In the US Army there were three grades of lieutenant – [[First lieutenant#United States|first]], [[Second lieutenant#United States|second]] and brevet second. The last grade, limited to one per company, was given to West Point graduates and others worthy of the promotion but for whom there was no vacancy. Regardless of grade, lieutenants acted as assistants to the captain, and in his absence the senior-most lieutenant took command.<ref>Kautz (1866), p. 17–21</ref> Among their various duties they might be assigned to take the daily roll-call, conduct inspections of the troops, and assist with recordkeeping;<ref>Kautz (1866), p. 22–26</ref> oversee the posting of guards when in camp or [[Picket (military)|pickets]] in the field, command [[patrolling|patrols]] or [[Bodyguard|escorts]] for general officers;<ref>Kautz (1866), p. 27–68</ref> and command [[Fatigue duty|fatigue parties]].<ref>Kautz (1866), p. 73–77</ref> Lieutenants were also chosen to serve on their regiment's staff,<ref>Kautz (1866), p. 171</ref> and may be assigned in an acting capacity to serve on the general staff of a higher unit.<ref>Kautz (1866), p. 188</ref>

===Enlisted personnel===
[[File:UnionOfficers.jpg|thumb|Non-commissioned officers of the [[93rd New York Infantry Regiment]] in [[Bealeton, Virginia]], in August 1863]]
[[Non-commissioned officers]] (NCOs) were important in the Union army in maintaining the order and alignment of formations during marches, battles, and transitioning between the two. [[Sergeants]] in particular were vital in this role as general guides and their selection ideally reserved for the most distinguished soldiers. NCOs were also charged with training individuals in how to be soldiers. While the captain or other company-level officers were responsible for training the soldiers when assembled into squads, platoons or as a company, experienced NCOs could take over this training as well.<ref name=Fisher119>Fisher (2001), pages 115–119</ref> NCOs were also responsible for the [[regimental colors]], which helped the unit maintain formation and serve as a rally point for the regiment. Typically a sergeant was designated the [[standard-bearer]] and protected by a [[color guard]] of [[corporal]]s who only opened fire in defense of the colors.<ref>Fisher (2001), pages 121–122</ref> There were a number of staff NCO positions including [[quartermaster sergeant]], [[ordnance sergeant]], and commissary sergeant.

NCOs in the volunteer forces were quite different from their regular counterparts as the war began. Appointed to their role as each regiment was created, they were often on a first-name basis with both their superior officers and the enlisted men they were tasked to lead. Discipline among friends and neighbors was not enforced as strictly as in the regular army, and while some NCOs brought with them prior battlefield experience (whether from the [[Mexican–American War]] or foreign military service) many at the start of the war were as equally ignorant as their officers in military matters.<ref name=Fisher119/><ref name=Fisher114>Fisher (2001), 109–114</ref> Training for these NCOs took place during off-duty hours and often involved lessons based on manuals such as [[William J. Hardee|''Hardee's Tactics'']]. One notable exception was [[Michigan in the American Civil War|Michigan]], which designated [[Fort Wayne (Detroit)|Fort Wayne]] as a training center for both officers and NCOs. As the war progressed NCOs gained valuable experience and even drastic disciplinary measures such as [[execution by firing squad]] were carried out when deemed necessary. The promotion of soldiers to NCOs (and NCOs to officers) was also increasingly based on battlefield performance, although each state maintained their own standards for when and where promotions could be granted.<ref name=Fisher119 /><ref name=Fisher114 />

;Enlisted ranks
{| border="1" cellpadding="2" cellspacing="0" style="margin:auto; width:100%;"
|-
! colspan=11| '''Enlisted Rank Structure'''
|-
! [[Sergeant Major#United States|Sergeant Major]]
! [[Quartermaster Sergeant#United States|Quartermaster Sergeant]]
! [[Ordnance Sergeant]]
! [[First Sergeant#United States|First Sergeant]]
! [[Sergeant#United States|Sergeant]]
! [[Corporal#United States|Corporal]]
! [[Musician (rank)|Musician]]
! [[Private E-2|Private]]
|-
! [[File:Union Army Infantry Sergeant Major.svg|80px]]
! [[File:Union Army Infantry Quartermaster Sergeant.svg|80px]]
! [[File:Union Army Infantry Ordnance Sergeant.svg|80px]]
! [[File:Union Army Infantry First Sergeant.svg|80px]]
! [[File:Union Army Infantry Sergeant.svg|80px]]
! [[File:Union Army Infantry Corporal.svg|80px]]
! No insignia
! No insignia
|}

*[[Sergeant major (United States)|Sergeant Major]]: The sergeant major was the senior-most enlisted soldier of a regiment and was expected to serve as a model for the other enlisted personnel. Appointed by the regiment's colonel, among his responsibilities was to issue orders to the first sergeants, maintain a roster of the sergeants and corporals detailed to various tasks, and assist the regimental adjutant in his duties. If a regiment didn't have a drum major or chief musician, he also had responsibility for overseeing the musicians.<ref>Kautz, A. V. (1864). Customs of Service for Non-commissioned Officers and Soldiers, as Derived from Law and Regulations, and Practised in the Army of the United States: Being a Handbook for the Rank and File of the Army, Showing what are the Rights and Duties, how to Obtain the Former and Perform the Latter, and Thereby Enabling Them to Seek Promotion and Distinction in the Service of Their Country. United States: J.B. Lippincott & Company. p. 172–174</ref>
*[[Quartermaster sergeant#American Civil War|Quartermaster Sergeant]]: The quartermaster sergeant was appointed by the regimental quartermaster to assist him in carrying out his duties. This included maintaining the store of supplies and serving as foreman for various work parties. Separately, each Union cavalry company was also authorized a quartermaster sergeant who performed similar tasks but was answerable to the company commander and first sergeant.<ref>Kautz (1864), p. 165–172</ref>
*Commissary Sergeant: Appointed by the regimental commissary, the commissary sergeant was responsible for assisting him in requisitioning and issuing rations to the regiment. Union cavalry companies and some artillery companies were also authorized a commissary sergeant to perform similar tasks.<ref>Kautz (1864), p. 152–164</ref>
*[[Hospital Steward]]: Regimental hospital stewards were responsible for the care of sick and wounded soldiers and their transportation to a general hospital, along with overseeing of any hospital property and medicines. Appointed by the colonel on the advice of the regiment's senior surgeon, they could direct any musicians (and later any [[U.S. Ambulance Corps|Ambulance Corps]] assets) to assist in carrying out these duties.<ref>Kautz (1864), p. 149–152</ref> Hospital stewards assigned to general hospitals acted as supervisors to the rest of the hospital staff (except for the doctors). A single steward was considered sufficient for a 150-bed hospital, while a 500-bed hospital would require three stewards: a chief steward charged with administration, one to act as pharmacist and a third overseeing the preparation of meals.<ref>Schroeder-Lein, G. R. (2015). ''The Encyclopedia of Civil War Medicine''. United Kingdom: Taylor & Francis. p. 281</ref>
*[[First Sergeant (United States)|First Sergeant]]: The first sergeant was the senior NCO of a company and appointed by the captain to serve as its immediate supervisor. Among his duties were taking roll call, arresting and confining soldiers for offenses committed, and overseeing the company stores (assisted by the company commissary and/or quartermaster sergeants if present).<ref>Kautz (1864), p. 131–149</ref>
*[[Sergeant (United States)|Sergeant]]: Sergeants were chosen from among a company's corporals and important for supervising the other soldiers. Each sergeant was in command of a squad of soldiers and directed them in carrying out their duties while in camp or garrison. In battle, sergeants kept the soldiers in ranks and prevented them from falling out; if necessary this included shooting them if they attempted to run away.<ref>Kautz (1864), p. 116–118</ref> Sergeants oversaw the changing of guards and pickets, confinement of prisoners (which, if numerous enough, would require one sergeant assigned as provost-sergeant), and led patrols and fatigue parties.<ref>Kautz (1864), p. 118–124</ref> One sergeant in the regiment would be chosen as the [[color sergeant]] and, protected by the [[color guard]], carried the [[regimental colors]] on parade and in battle.<ref name=Kautz64p130>Kautz (1864), p. 130–131</ref> 
:Sergeants in the artillery branch commanded individual cannons as the Chief of Piece and were responsible for keeping it maintained and directing its use in battle.<ref>Kautz (1864), pages 124–125</ref> Sergeants of the Ordnance Department (distinct from the separate rank of [[Ordnance Sergeant]]) were employed at the various arsenals and armories with manufacturing and caring for the various arms and equipment. They were referred to as master armorers, master carriage-makers or master blacksmiths early in the war.<ref name=Kautz64p65>Kautz (1864), pages 64–65</ref> Sergeants of the Corps of Engineers, in addition to the normal duties of a sergeant, also had to be knowledgeable in the construction of bridges, forts and other military engineering projects.<ref name=Kautzp66>Kautz (1864), page 66</ref> In the Signal Corps, a sergeant was assigned to each signal officer, from whom he took instruction in order to assist with the sending and receiving of signals and performing mounted reconnaissance.<ref name=Kautz64p67>Kautz (1864), pages 67–68</ref>
*[[Corporal (United States)|Corporal]]: The lowest grade of NCO, corporals would be chosen from among a company's most competent privates and given charge of various tasks and duties. They might be given charge of small parties carrying out fatigue, police or guard duties, and in the absence of the sergeant they may take on their duties.<ref name=Kautz64p102>Kautz (1864), pages 102–111</ref> The five most distinguished corporals of a regiment would be chosen to act as the color guard and accompany the color sergeant.<ref name=Kautz64p130/>
:Artillery corporals acted as gunners and would assist the Chief of Piece in maintaining and aiming the cannon.<ref name=Kautz64p102/> As with sergeants, corporals of the Ordnance Department were employed at its various facilities. Their formal titles were armorer, carriage-maker or blacksmith until revised later in the war.<ref name=Kautz64p65/> Likewise, corporals in the Corps of Engineers were also required to be knowledgeable in practical military engineering in addition to their soldierly skills.<ref name=Kautzp66/>
*[[Private (United States)|Private]]: Privates carried out the basic functions of being a soldier in the Union army. When in camp or garrison they filled in on the various work details and fatigue parties, stood guard and policed the local area. They might be assigned to extra duties such as the company cook, tailor, clerk or as orderlies.<ref>Kautz (1864), pages 22–44</ref> In the field they were employed in tasks commiserate with their roles as infantry, cavalry or artillery soldiers. This included being deployed as pickets, skirmishers or flankers.<ref>Kautz (1864), pages 44–60</ref> 
:Soldiers could also be employed in special duties that were not strictly military in nature: mechanics and laborers, hospital attendants and cooks, regimental armorers, officers' servants, [[Pioneer (military)|pioneers]], [[courier]]s, [[reconnaissance|scouts]] and [[espionage|spies]].<ref>Kautz (1864), pages 91–96</ref> In the Corps of Engineers, Ordnance Department, and Signal Corps, privates were further differentiated as first class or second class. First class Engineer and Ordnance privates were formerly referred to as [[Armed-forces artificer|artificers]], while second class privates were formerly referred to as laborers.<ref name=Kautz64p65/><ref name=Kautz64p67/><ref>Kautz (1864), page 287</ref>

===Southern Unionists===
Southerners who were against the Confederate cause during the Civil War were known as [[Southern Unionists]]. They were also known as Union Loyalists or Lincoln's Loyalists. Within the eleven Confederate states, states such as [[Tennessee]] (especially [[East Tennessee]]), [[Virginia]] (which included [[West Virginia]] at the time), and [[North Carolina]] were home to the largest populations of Unionists. Many areas of [[Appalachia|Southern Appalachia]] harbored pro-Union sentiment as well. As many as 100,000 men living in states under Confederate control would serve in the Union army or pro-Union guerilla groups. Although Southern Unionists came from all classes, most differed socially, culturally, and economically from the region's dominant pre-war [[planter class]].<ref>Scott, E. Carele. [https://warfarehistorynetwork.com/2018/12/21/southerner-vs-southerner-union-supporters-below-the-mason-dixon-line/ Southerner vs. Southerner: Union Supporters Below the Mason-Dixon Line]. ''Warfare History Network''. Retrieved August 1, 2022.</ref>

===Ethnic composition===
[[File:Us colored volunteer infantry.jpg|thumb|The 26th U.S. Colored Volunteer Infantry of the [[United States Colored Troops|U.S. Colored Troops]] at [[Camp William Penn]] in present-day [[Cheltenham Township, Montgomery County, Pennsylvania|Cheltenham Township, Pennsylvania]], in 1865]]
[[File:John Haag, Co. B, 26th Wis. Volunteer Infantry.jpg|thumb|John Haag, a 21-year-old immigrant from [[Germany]], affiliated with Company B of the [[26th Wisconsin Infantry Regiment]] in August 1862<ref>''Chippewa County, Wisconsin Past and Present'', Volume II.  Chicago:  S.J. Clarke Publishing Company, 1913.  p. 258.</ref>]]
Native-born White Americans made up roughly two-thirds of the soldiers in the Union army, with the rest of many different ethnic groups, including large numbers of immigrants. About 25% of the white men who served in the Union army were foreign-born.<ref name="McPherson, pp.36–37"/> The U.S. experienced its heaviest rate of immigration during the 1850s, and the vast majority of these people moved to the [[Northeastern United States|Northeastern]] states. 

Among these immigrants, [[German Americans in the American Civil War|Germans]] constituted the largest group with a million arrivals between 1850 and 1860, many of them [[Forty-Eighters]]. Nearly as many [[Irish Americans in the American Civil War|Irish]] immigrants arrived during the same period.<ref>Germans in the Civil War: The Letters They Wrote Home. (2009). United States: University of North Carolina Press. p. 2</ref> Immigrant soldiers were among the most enthusiastic in the Union army, not only from a desire to help save their adoptive home but to prove their patriotism towards it.<ref name=Axelrod73>Axelrod, A. (2017). Armies South, Armies North. United States: Lyons Press. p. 72-73</ref>  To help cement immigrant enthusiasm and loyalty to the Union, several generals were appointed from these communities, including [[Franz Sigel]] and [[Michael Corcoran]].<ref>Axelrod, A. (2017), p. 86-87</ref>

{| class=wikitable style="text-align:right;"
|+Ethnic composition of Union enlistments<ref>{{cite web|url=https://emergingcivilwar.com/2016/04/08/the-cosmopolitanism-of-the-union-army-what-did-it-mean/|title=The Cosmopolitanism of the Union Army: What Did It Mean?|first=Matt|last=Stanley|website=Emerging Civil War|date=8 April 2016|access-date=9 December 2022}}</ref> 
!Estimates
!Origin
|-
|1,400,000 || align=left |Native-born [[White American]]
|-
|216,000 || align=left |[[Germans]]/[[German-American]]<ref>{{cite book|url=https://books.google.com/books?id=aGgrKlWxpu8C&pg=PA15|title=The Blessed Peace of Freedom: Europeans in Civil War America|first=Dean. B|last=Mahin|page= 15|date=2002|publisher=Potomac Books |isbn=9781574884845 }}</ref>
|-
|210,000 || align=left |[[African American]]
|-
|150,000 || align=left |[[Irish-American|Irish]]-born<ref>{{cite book|url=https://books.google.com/books?id=aGgrKlWxpu8C&pg=PA21|title=The Blessed Peace of Freedom: Europeans in Civil War America|first=Dean. B|last=Mahin|page= 21|date=2002|publisher=Potomac Books |isbn=9781574884845 }}</ref><ref>{{cite book|url=https://books.google.com/books?id=oCYVCgAAQBAJ&pg=PA100|title=Civil War Citizens: Race, Ethnicity, and Identity in America's Bloodiest Conflict|first = Susannah J.|last=Ural|page= 100|year= 2010|publisher=NYU Press |isbn=9780814785706 }}</ref>
|-
|18,000 – 50,000 || align=left |[[Canadian Americans|Canadian]]{{efn|Alternative estimates place the number of enlistees much lower.<ref name=Reid>Reid, R. M. (2014). African Canadians in Union Blue: Volunteering for the Cause in the Civil War. Canada: UBC Press. p. 229</ref><ref name=Winks>Winks, R. W. (1998). Civil War Years: Canada and the United States. Ukraine: McGill-Queen's University Press. p. 179-185</ref>}}
|-
|50,000 || align=left |[[English Americans|English]]-born
|-
|49,000 || align=left |Other ([[Scandinavian American|Scandinavian]], [[Italian American|Italian]], [[Jewish American|Jewish]], [[Mexican American|Mexican]], [[Polish American|Polish]], [[Native Americans in the United States|Native American]])
|-
|40,000 || align=left |[[French Americans|French]]/[[French-Canadian Americans|French-Canadian]]
|-
|colspan="2"|{{Notelist}} 
|}

Many immigrant soldiers formed their own regiments, such as the [[Irish Brigade (United States)|Irish Brigade]], including the [[69th Infantry Regiment (New York)|69th New York]], 63rd New York, 88th New York, 28th Massachusetts, 116th Pennsylvania; the Swiss Rifles (15th Missouri); the [[55th New York Volunteer Infantry|Gardes de Lafayette]] (55th New York); the Garibaldi Guard (39th New York); the Martinez Militia (1st New Mexico); the Polish Legion (58th New York); the [[German Rangers]]; Sigel Rifles (52nd New York, inheriting the 7th); the Cameron Highlanders ([[79th New York Volunteer Infantry]]); and the Scandinavian Regiment (15th Wisconsin).<ref name=Axelrod73/> But for the most part, the foreign-born soldiers were scattered as individuals throughout units.<ref>{{Cite web |url=http://52ndnysv.com/ |title=The 52nd New York State Volunteers |access-date=May 30, 2019 |archive-date=July 1, 2016 |archive-url=https://web.archive.org/web/20160701083816/http://52ndnysv.com/ |url-status=dead }}</ref>

The Confederate army was less diverse: 91% of its soldiers were native-born white men and only 9% were foreign-born white men, with Irish being the largest group, other groups included Germans, French, British, and Mexicans. Most Mexicans happened to have been born when the [[Southwestern United States|Southwest]] was still part of [[Mexico]]. Some Confederate propaganda condemned foreign-born soldiers in the Union army, likening them to the German [[Hessian (soldiers)|Hessian]] troops who fought alongside the [[British Army during the American Revolutionary War]]. A relatively smaller number of [[Native Americans in the United States|Native Americans]], including members of [[Cherokee]], [[Chickasaw]], [[Choctaw]] and [[Muscogee]] peoples, fought for the Confederacy.

====Italian Americans in the Union army====
{{Main|Italian Americans in the Civil War}}
The great majority of [[Italian Americans]], for both demographic and ideological reasons, served in the Union army (including generals [[Edward Ferrero]] and [[Francis B. Spinola]]). Six Italian Americans received the [[Medal of Honor]] during the war, among whom was Colonel [[Luigi Palma di Cesnola]], who later became the first Director of the [[Metropolitan Museum of Arts]] in New York (1879–1904). Most of the Italian-Americans who joined the Union army were recruited from [[New York City]]. Many Italians of note were interested in the war and joined the army, reaching positions of authority. Brigadier General [[Edward Ferrero]] was the original commander of the [[51st New York Volunteer Infantry|51st New York Regiment]].<ref>Belfiglio, p. 169</ref> He commanded both brigades and divisions in the [[Eastern Theater of the American Civil War|eastern]] and [[Western Theater of the American Civil War|western]] theaters of war and later commanded a division of the [[United States Colored Troops]]. Colonel Enrico Fardella, of the same and later of the [[85th New York Volunteer Infantry|85th New York]] regiment, was made a [[Brevet (military)|brevet]] brigadier general when the war ended. [[Francis B. Spinola]] recruited four [[regiment]]s in New York, was soon appointed Brigadier General by President [[Abraham Lincoln]] and given command of the [[Spinola Brigade]]. Later he commanded another unit, the famed [[Excelsior Brigade]].
[[File:March past of the 'Garibaldi Guard' before President Lincoln, 1861-1865 (c1880).jpg|thumb|Review of the [[Garibaldi Guard]] by President [[Abraham Lincoln]]]]

The [[Garibaldi Guard]] recruited volunteers for the Union army from Italy and other European countries to form the [[39th New York Volunteer Infantry Regiment|39th New York Infantry]].<ref>''Images: A Pictorial History of Italian Americans''. New York, 1986, p.26</ref> At the outbreak of the American Civil War, [[Giuseppe Garibaldi]] was a very popular figure. The [[39th New York Volunteer Infantry Regiment]], of whose 350 members were Italian, was nicknamed ''Garibaldi Guard'' in his honor. The unit wore red shirts and ''[[Bersaglieri|bersaglieri plumes]].'' They carried with them both a Union Flag as well as an [[Italian flag]] with the words ''Dio e popolo,'' meaning "God and people."<ref>{{cite journal |last1=Belfiglio |first1=Valentino J. |title=Italians and the American Civil War |journal=Italian Americana |date=Spring–Summer 1978 |volume=4 |issue=2 |page=164 |jstor=41330626 |url=https://www.jstor.org/stable/41330626 |access-date=21 December 2022}}</ref> In 1861 Garibaldi himself volunteered his services to President [[Abraham Lincoln]]. Garibaldi was offered a major general's commission in the U.S. Army through the letter from Secretary of State [[William H. Seward]] to [[Henry Sanford|H. S. Sanford]], the U.S. Minister at [[Brussels]], July 17, 1861.<ref>Mack Smith, Denis, Garibaldi, Prentice-Hall, 1969, pp. 69&ndash;70</ref>

Colonel [[Luigi Palma di Cesnola]], a former Italian and British soldier and veteran of the [[Crimean War]], commanded the 4th New York Cavalry and would rise to become one of the highest ranking Italian officer in the Union army.<ref>Belfiglio, p. 167</ref> He established a military school in New York City where many young Italians were trained and later served in the Union army. Di Cesnola received the [[Medal of Honor]] for his actions during the [[Battle of Aldie]].<ref>{{cite web |title=LOUIS PALMA DI CESNOLA |url=https://www.cmohs.org/recipients/louis-p-di-cesnola |publisher=Congressional Medal of Honor Society |access-date=21 December 2022}}</ref> Two more famous examples were Francesco Casale and Luigi Tinelli, who were instrumental in the formation of the [[39th New York Volunteer Infantry Regiment|39th New York Infantry Regiment]]. According to one evaluation of the [[Official Records of the Union and Confederate Armies]], there were over 200 Italians who served as officers in the U.S. army.<ref>Belfiglio, p. 167</ref>

====African Americans in the Union army====
{{Main|Military history of African Americans in the American Civil War|United States Colored Troops}}
[[File:Unidentified African American Union soldier with a rifle and revolver in front of painted backdrop showing weapons and American flag at Benton Barracks, Saint Louis, Missouri LOC 5229147154 (cropped).jpg|thumb|Portrait of an African American Union soldier at [[Benton Barracks]]]]
By 1860, the [[African American]] or Black population of the United States consisted of four million [[Slavery in the United States|enslaved]] and half a million [[Free Negro|free Blacks]].  When the Civil War began, many freedmen in the North attempted to enlist in federal service but were barred from doing so. Popularly-held prejudices doubted whether Black people could be effective soldiers, and President Lincoln believed allowing their enlistment would anger Northern whites and alienate not just the South but the [[Border states (American Civil War)|Border States]] too.  However he eventually changed his mind and persuaded Congress to authorize the first official Black enlistment system in late 1862, which evolved into the [[United States Colored Troops]].<ref name=USCT>American Civil War: The Definitive Encyclopedia and Document Collection [6 Volumes]: The Definitive Encyclopedia and Document Collection. (2013). United States: ABC-CLIO. p. 10-12, 14–15</ref>

Before they were allowed to enlist, many Black people volunteered their services to the Union army as cooks, nurses, and in other informal roles, and several volunteer regiments of Black troops were raised by the states. These included the [[1st Kansas Colored Infantry Regiment]], the first Black regiment to be raised and the first to engage in combat; the [[1st Louisiana Native Guard (Union)|1st Louisiana Native Guard]], raised from both freedmen and escaped slaves after the [[Capture of New Orleans]]; and the [[54th Massachusetts Infantry Regiment]], which became the most famous Black unit after their valiant participation in the [[Battle of Fort Wagner, Morris Island|Battle of Fort Wagner]].  Their efforts helped to dispel the notion that Black soldiers were a liability, allowing about 200,000 Black soldiers to serve in the Union army during the Civil War.<ref name=USCT/>

Even as they served their country, Black soldiers were subject to discrimination. They were more often assigned to menial labor. Some Union officers refused to employ them in combat, but when they were they often had to use inferior weapons and equipment.  Black soldiers were paid less than white soldiers ($10 vs $16 per month) until Congress yielded to public pressure and approved equal pay in June 1864. Black units were led predominantly by white officers, and while more than a hundred Black men were eventually made officers (not counting those [[Passing (racial identity)|passing]] as white), none were promoted to a rank higher than major.  If captured by Confederate forces, Black soldiers risked being made slaves or [[summarily executed]].<ref name=USCT/>

===Women in the Union army===
[[File:Kady Brownell CDV.jpg|thumb|[[Kady Brownell]], a [[vivandière]] from [[Rhode Island in the American Civil War|Rhode Island]]]]
Women took on many significant roles in the Union army and were important to its ultimate success on the battlefield.  The most direct way they could help was to enlist and fight as soldiers, although women were officially barred from doing so.  Nevertheless, it is believed [[List of female American Civil War soldiers|hundreds of women]] disguised themselves as men in order to enlist.  While many were discovered and forced to quit, others were only found out after they were killed in combat, and a number managed to serve throughout the entire war with their true identity successfully concealed.

One of the more traditional roles played by women in the Union army was that of [[camp follower]]s.  Thousands of white and Black women accompanied Union armies in an unofficial capacity to provide their services as [[Cooking|cook]]s, [[laundress]]es, [[nurse]]s and/or [[prostitute]]s.  Many were the wives or other female relatives of the soldiers themselves who saw to their personal needs and (if time allowed) looked to the well-being of other soldiers.  A somewhat more formal role for some camp followers was that of ''[[vivandière]]''.  Originally a female [[sutler]], the role of ''vivandière'' expanded to include other responsibilities, including on the battlefield.  Armed for their own protection, they brought water to thirsty soldiers, carried the [[regimental colors]] and rallied their fellow soldiers to fight, provided [[first aid]] or helped the wounded back to a field hospital.  A related (and sometimes conflated) role was that of "daughter of the regiment".  Often literally a daughter of one of the regimental officers, these women looked to the soldiers' well-being but also served as their regiment's "mascot" who inspired the men by wearing stylish clothing and enduring the same hardships as them.  Some of the most prominent women to accompany the Union armies in the field include [[Anna Etheridge]], [[Marie Tepe]], and [[Nadine Turchin]].<ref>Cordell, M. R. (2016). Courageous Women of the Civil War: Soldiers, Spies, Medics, and More. United States: Chicago Review Press. Part IV: Vivandière</ref><ref>Tsui, B. (2006). She Went to the Field: Women Soldiers of the Civil War. United States: TwoDot. p. 73-80</ref><ref>Harper, J. E. (2004). Women During the Civil War: An Encyclopedia. Taylor & Francis. p. 53–59</ref>

Women also sought to serve more formally as nurses in the Union army, many having been inspired by the work of [[Florence Nightingale]] during the [[Crimean War]].  However, there was strong resistance against these efforts at first.  Societal prejudices saw women as too delicate and the job too unsuitable for women of social rank, particularly at the thought of unmarried women surrounded by thousands of men in close quarters.  Nevertheless, Congress eventually approved for women to serve as nurses, to which [[Dorothea Dix]] – appointed Superintendent of Army Nurses – was responsible for setting hiring guidelines and starting a training program for prospective candidates.  For the women who served, nursing during the Civil War was a hazardous occupation: grueling hours spent in close proximity to deadly diseases and nearby battlefields resulted in many suffering permanent disabilities or death.  Added to this were the prejudices of the male medical officers in charge who did not want them there and frequently clashed with the nurses over issues of [[triage]], patient treatments and [[hospice care]].  Tens of thousands of women served as nurses for the Union army, among whom are included [[Clara Barton]], [[Susie King Taylor]], [[Mary Edwards Walker]], and [[Louisa May Alcott]].<ref>Cordell (2016), Part III: Nurses</ref><ref>Harper (2004), p. 285–292</ref>

No less vital were the thousands of women who provided service to the Union army in the field of [[espionage]].  Early in the war, women were at a distinct advantage as [[Spying|spies]], [[Reconnaissance|scouts]], [[smuggler]]s, and [[saboteur]]s: the idea of women participating in such dangerous lines of work was simply not considered.  Eventually though their opponents recognized their existence, and while female spies caught in the act were not typically executed like their male colleagues, they still faced the threat of lengthy prison sentences.   For self-evident reasons many of these activities were kept secret and any documentation (if it existed) was often destroyed.  As such the identity of many of these women will never be known.  Of those who became famous for their espionage work during or after the end of the war, prominent examples include [[Harriet Tubman]], [[Mary Louvestre]], [[Pauline Cushman]], [[Elizabeth Van Lew]], and [[Mary Bowser]].<ref>Cordell (2016), Part II: Spies</ref><ref>Harper (2004), p. 348–350</ref>

==Motivations==
===Anti-slavery sentiment===
In his 1997 book examining the motivations of the American Civil War's soldiers, [[For Cause and Comrades: Why Men Fought in the Civil War|''For Cause and Comrades'']], historian [[James M. McPherson]] states that Union soldiers fought to preserve the United States, as well as to end slavery, stating that:

{{blockquote|text=While restoration of the Union was the main goal for which they fought, ''they became convinced that this goal was unattainable without striking against slavery.''|author=James M. McPherson|source=''[[For Cause and Comrades: Why Men Fought in the Civil War]]'' (1997), p. 118, emphasis added.<ref name=JMMcPherson1997p118>{{Cite book|url=https://archive.org/details/forcausecomrades00mcph|url-access=registration|title=For Cause and Comrades: Why Men Fought in the Civil War|page=[https://archive.org/details/forcausecomrades00mcph/page/118 118]|last=McPherson|first=James M.|date=1997|publisher=Oxford University Press, Inc.|oclc=34912692|location=New York City|author-link=James M. McPherson|isbn=0-19-509-023-3|access-date=March 10, 2016|quote=While restoration of the Union was the main goal for which they fought, they became convinced that this goal was unattainable without striking against slavery.}}</ref>}}

McPherson states that witnessing the slave system of the Confederacy first-hand also strengthened the [[anti-slavery]] views of Union soldiers,<ref name=JMMcPherson1997p118/> who were appalled by its brutality.<ref name=JMMcPherson1997p118/> He stated that "Experience in the South reinforced the antislavery sentiments of many soldiers."<ref name=JMMcPherson1997p118/> One [[Pennsylvania in the American Civil War|Pennsylvanian]] Union soldier spoke to a slave woman whose husband was whipped, and was appalled by what she had to tell him of slavery. He stated that "I thought I had hated slavery as much as possible before I came here, but here, where I can see some of its workings, I am more than ever convinced of the cruelty and inhumanity of the system."<ref name=JMMcPherson1997p118/>

==Army administration and issues==
===Adjutant General's Department===
{{main|United States Army Adjutant General's Corps}}
[[File:Gen. Lewellyn F. Haskell - NARA - 528379 Restored.jpg|thumb|right|[[Llewellyn F. Haskell]] (1842–1929), [[United States Army]] officer and a Union [[General officer|general]] during the [[American Civil War]]]]

The responsibilities and functions of the Adjutant General's Department (AGD) were many and varied during the course of the Civil War, but principle among them was handling military correspondence between the President, Secretary of War and General-in-Chief, and the rest of the army. Other functions included administering recruitment, overseeing the appointment of [[chaplain]]s, maintaining personnel records, and issuing instruction books and other [[Form (document)|forms]]. During the war, some of the department's responsibilities and functions were spun off to new offices while new ones were added. The recruitment of new white volunteers and draftees, and the suppression and punishment of [[absenteeism]] and [[desertion]], was given to the newly formed Provost Marshal General's Bureau in May 1863, while the position of [[Commissioner for the Exchange of Prisoners]] was created to take over this function from the AGD. The [[Bureau of Colored Troops]] was created within the AGD specifically to oversee the creation of the [[United States Colored Troops]], and in the final year of the war the AGD was given the responsibility for collecting and editing documents which would constitute ''The War of the Rebellion: A Compilation of the Official Records of the Union and Confederate Armies''.<ref name="Newell90">Newell & Shrader, p. 85-90</ref>

At the start of the Civil War, the AGD numbered just fourteen regular officers: the [[United States Army Adjutant General's Corps|Adjutant General]] (AG) with the rank of colonel, a lieutenant-colonel, four brevet majors, and eight brevet captains. In August 1861 the AG was raised to major-general and the strength of the AGD increased to twenty officers, and a year later it was reorganized to constitute the AG, two colonels, four lieutenant-colonels, and thirteen majors. The small number of civilian clerical staff supporting the officers was also increased as the war progressed, including the addition of up to ten noncommissioned officers by 1862. However to meet the need for assistant adjutant generals authorized for each corps, division and brigade, appointments were made from among the volunteer forces, and by 1865 there were an additional 85 majors and 256 captains serving in these capacities. At the regimental level, one of the unit's lieutenants would be selected to serve as its adjutant.<ref name="Newell90"/>

In spite of the rapid increase of the army at the start presenting numerous challenges and being perpetually understaffed throughout the war, the AGD appears to have handled its responsibilities competently and with little disruption. The AGD also had fewer conflicts with field commanders compared to some of the other departments, partly because its authority was well-established and issued few controversial orders itself, and it was less affected by matters of procurement and emerging technologies.<ref name="Newell90"/>

;Leadership
Colonel [[Lorenzo Thomas]] was named Adjutant General of the army on March 7, 1861, one day after Col. [[Samuel Cooper (general)|Samuel Cooper]] resigned the join the Confederacy.  While Thomas served as the AG throughout the entirety of the war, he eventually ran afoul of Secretary Stanton, who reassigned him to the job of recruiting soldiers for black regiments in the [[Western Theater of the American Civil War|western theater]].  From March 1863 on then, the assistant adjutant general Colonel [[Edward D. Townsend]] essentially was the acting AG in Washington.<ref name="Newell90"/>

===Bureau of Military Justice===
{{main|Judge Advocate General's Corps, United States Army}}
An office of the [[Judge Advocate]] had existed in the US Army since its founding, consisting at the start of the Civil War of a single officer with the rank of major and small civilian clerical staff in Washington.  It was not until after the war began however that Congress formally authorized the appointment of a [[Judge Advocate General]] (JAG) and creation of the Bureau of Military Justice, a [[de facto]] department and forerunner to a true Judge Advocate General's Department.  The principle functions of the JAG included conducting [[Courts-martial of the United States|courts-martial]] and [[inquiry|inquiries]]; codifying the [[law of war|laws of war]] and the [[Uniform Code of Military Justice|military laws of the United States]]; reviewing the records of courts-martial, military commissions and inquiries; and asserting the jurisdiction of military commissions over civilians in times of war.<ref name="Newell98">Newell & Shrader, p. 94-98</ref>

To meet the demands of a vastly larger army, Congress authorized in July 1862 the appointment of a JAG with the rank of colonel and for President Lincoln to appoint a judge advocate of volunteers with the rank of major for each army in the field.  These judge advocates were to advise commanders on legal issues, prosecute offenses, and review and maintain the records of courts-martial and other proceedings in the field.  A year later, Congress legislated the creation of the Bureau of Military Justice, gave it an [[appellant]] function, and authorized the JAG to head it as a brigadier general alongside an assistant JAG with the rank of colonel.  With these authorizations came a small increase in the size of the clerical staff assisting the JAG.<ref name="Newell98"/>

During the war the JAG and his subordinates were able to satisfactorily handle the increased volume and complexity of legal matters that came with the exponential growth of the army.  Among their most important accomplishments was the creation of the [[Lieber Code]] and, for the first time, collecting all precedents, decisions and opinions which had become US military law into a single digest and publishing it in early 1865.  One of the most controversial issues associated with the bureau was the use of military commissions to try civilians, an issue which would not be settled until ''[[Ex parte Milligan]]'' was decided in 1866.<ref name="Newell98"/>

;Leadership
The Civil War began with brevet Major [[John F. Lee]] serving as the judge advocate of the army until September 3, 1862, when [[Joseph Holt]] was formally appointed as JAG.  Holt played an important parts in helping to expanding the office of the JAG and oversaw some of the most important and sensitive trials of the war.  However Holt also made many enemies while JAG and was severely criticized for his handling of the [[Assassination of Abraham Lincoln#Conspirators' trial and execution|trial of President Lincoln's assassins]].<ref name="Newell98"/>

===Bureau of Refugees, Freedmen, and Abandoned Lands===
{{main|Freedmen's Bureau}}
In March 1865 the Bureau of Refugees, Freedmen, and Abandoned Lands was created by Congress with a mandate to see to the needs of all Black freedmen and white refugees, and the management of all lands within the rebel states which had been abandoned or otherwise come into the possession of the United States.  It consisted of a commissioner as head of the bureau, an assistant commissioner for each of the rebel states, and a small staff of one chief and nine other clerks.  Additionally, any military officer could be assigned to duty on behalf of the bureau.  Major General [[Oliver Otis Howard]] was appointed to head the bureau at its creation and lead it throughout its lifetime.  While the Freedmen's Bureau was the center of much controversy during the [[Reconstruction era]] and some of the relief it provided was less than satisfactory, its most important contribution was in providing education to many Blacks and poor whites.<ref name="Newell107">Newell & Shrader, p. 106-107</ref>

===Corps of Engineers===
{{Main|United States Army Corps of Engineers}}
The Corps of Engineers was a small part of the army prior to the Civil War but played an important role not only in the conflict but for the nation as a whole.  The Corps was responsible for running the [[United States Military Academy]] at [[West Point, New York|West Point]], which supplied officers to all branches but whose top graduates were commissioned into the Corps. They were not only involved with [[military engineering]] such as constructing [[fortifications]] and harbor defenses but also oversaw [[civil engineering]] including building canals, bridges and similar projects. This focus on civil works did prevent the Corps from devoting its entire effort to the war though.<ref name="Newell292">Newell & Shrader, p. 285–292</ref><ref name="Baldwin18">Baldwin, W. (2008). ''The U.S. Army Corps of Engineers: A History''. United States: Headquarters, U.S. Army Corps of Engineers, Office of History. p. 15–18</ref> Corps personnel acted as [[combat engineer]]s during battle, helping to construct [[pontoon bridge]]s, repair roads and bridges, dig [[Trench warfare|trenches]], and conduct [[Engineer reconnaissance|reconnaissance]]. The Corps also exerted an influence beyond its small size as many of the Union's most prominent officers, including McClellan and Meade, were themselves trained as engineers and used their knowledge to influence the outcome of battles.<ref name="Newell292" /><ref name="Baldwin110">Baldwin, p. 107–110</ref>

Prior to the war, the Corps of Engineers consisted of just forty-eight officers and a single company of 150 engineer troops.  Engineer Company A was first created for the [[Mexican–American War]] and guarded President Lincoln at his [[First inauguration of Abraham Lincoln|first inauguration]].<ref name="Newell292" /><ref name="Baldwin110" /> It was organized with ten sergeants (master-workmen), ten corporals (overseers), two musicians, sixty-four first-class privates ([[Armed-forces artificer|artificers]]) and sixty-four second-class privates (laborers).<ref>Callan, J. F. (1864). The Military Laws of the United States, Relating to the Army, Volunteers, Militia, and to Bounty Lands and Pensions, from the Foundation of the Government to 4 July 1864: To which are Prefixed the Constitution of the United States (with an Index Thereto,) and a Synopsis of the Military Legislation of Congress During the Revolutionary War. United States: G.W. Childs. p. 24–25</ref> In August 1861 Congress authorized the formation of three more companies to be organized the same as Engineer Company A, with all four organized into a single battalion (the US Engineer Battalion, later [[1st Engineer Battalion (United States)|1st Engineer Battalion)]], and the addition of two lieutenant colonels, four majors and six lieutenants to the Corps. The battalion had no formal headquarters but fell under the command of the most senior officer present. In March 1863, when the Corps of Topographical Engineers was disbanded and its function merged with the Corps of Engineers, Congress further revised the Corps to consist of a brigadier-general as Chief Engineer, four colonels, ten lieutenant-colonels, twenty majors, thirty captains, thirty first lieutenants and ten second lieutenants.<ref name="Newell292" /><ref name="Baldwin110" />

The US Engineer Battalion served ably as part of the Army of the Potomac, but on its own was insufficient to see to the army's need for engineers throughout the different theaters of war. A small number of volunteer engineer regiments were formed during the war, including the [[1st Michigan Engineers and Mechanics Regiment]], the [[1st New York Engineer Regiment]] and the [[1st United States Veteran Volunteer Engineer Regiment]]. However, in many cases engineering work was carried out by line soldiers under the supervision of officers with engineering backgrounds, if any were available.<ref name="Newell292" /><ref name="Baldwin110" /> Most types of engineering work, such as digging simple [[Earthworks (military)|earthworks]] or laying small bridges, did not require the specialized skills of engineers, which were required for complex endeavors like constructing pontoon bridges or forts. Union armies typically detailed soldiers to form company-sized detachments of [[Pioneer (military)|pioneers]] to repair roads or bury the dead after a battle.<ref>Hess, E. J. (2005). ''Field Armies and Fortifications in the Civil War: The Eastern Campaigns, 1861–1864'' (Civil War America). United Kingdom: University of North Carolina Press. p. 15–16</ref>
;Leadership
*[[Joseph Gilbert Totten]]: December 7, 1838{{spaced ndash}}April 22, 1864
*[[Richard Delafield]]: April 22, 1864{{spaced ndash}}August 8, 1866

===Corps of Topographical Engineers===
{{main|United States Army Corps of Topographical Engineers}}
The Corps of Topographical Engineers had been established in 1831 with the mission of [[exploration]], [[surveying]], and [[cartography]], particularly in the [[American West]].  Topographical engineers (or "topogs") including [[John C. Frémont]], [[Howard Stansbury]], [[William H. Emory]] and [[Gouverneur K. Warren]] were instrumental in the westward expansion of the United States.<ref name="Baldwin27">Baldwin, p. 21-27</ref>  During the war, the civilian nature of the Corps' mission was largely suspended and it undertook the role of reconnaissance, construction of defensive works and supplying maps to the army.  In these conditions drawing a distinction between the two corps became increasingly impractical, until in March 1863 the Corps of Topographical Engineers was disbanded and its mission taken up by the Corps of Engineers.<ref name="Newell292"/>

The Topographical Engineers numbered forty-five officers before the Civil War.  In August 1861 an additional two lieutenant colonels, four majors and six lieutenants were authorized by Congress. There were no enlisted men in the Corps, although when the Corps was expanded Congress also authorized a company of engineers for the Topographical Engineers to be modeled after the Corps of Engineers.  However this company was never formed, and the actual size of the Corps shrank as a number retired, died, defected to the Confederacy or became general officers of the volunteers, until eventually the remaining officers were absorbed by the Corps of Engineers.<ref name="Newell292"/>

The most important role played by the Topographical Engineers, even after their merger with the regular Corps, was providing desperately-needed maps to army commanders.  Each field army headquarters established their own topographical departments under the supervision of engineer officers, which would provide the army with maps necessary for a given campaign.  Such departments themselves were staffed with teams of [[Drafter|draughtsmen]] and assistants and stocked with [[printing press]]es, [[photographic]] and [[lithographic]] equipment.<ref name="Newell292"/>
;Leadership
The Chief of Topographical Engineers at the start of the Civil War was Colonel [[John James Abert]].  Colonel Abert had been responsible for lobbying Congress to make the Corps an independent branch of War Department and was appointed to lead his creation in 1838.  He retired in September 1861 and was replaced by [[Stephen Harriman Long]], who remained in the position until the Corps was disbanded.  Thereafter he continued to serve in the Corps of Engineers as the senior officer to the Chief Engineer.<ref name="Baldwin27"/><ref>Baldwin, p. 283</ref>

===Inspector General's Department===
{{main|Office of the Inspector General of the United States Army}}
At the start of the Civil War, there was technically no Inspector General's Department, with neither a set of operating practices or centralized direction.  Instead there were two [[Inspector General]]s (IGs) with the rank of colonel whose duty was to conduct inspections and investigations to ensure the army was organized and operating at full readiness, but these were done in an ad-hoc manner at the discretion of the Secretary of War.  As the war progressed and membership in the inspectorate increased, the duties of IGs and assistant IGs were continually redefined, to the extent that any time a problem was identified the common response was simply to assign an inspector to it.  Eventually in January 1863 a permanent office of the IG was established in Washington, and it was from here that the process of exerting a centralized control over IGs in the field and crafting standard policies and procedures was started.<ref name="Newell94">Newell & Shrader, p. 90–94</ref>

In August 1861, Congress authorized an increase of two additional IGs with the rank of colonel and five assistant IGs with the rank of major from among the regular army.  This number stayed the same throughout the entire war, with the addition of a small civilian clerical staff once the Washington office was established.  Congress eventually determined that each geographical department, army, corps, division and brigade would also be assigned an IG or assistant IG, however these positions were to be filled by regular or volunteer officers detailed from line units of the army or from the other staff departments.<ref name="Newell94"/>

The inspectorate faced many challenges during the Civil War, including hostility and lack of cooperation from some commanders and the mixed performance of some IGs in the field.  Despite these issues it was able to successfully meet the challenges of the war overall, particularly with bringing under control the waste, fraud and abuse which had been rampant at the start of the conflict.<ref name="Newell94"/>
;Leadership
At the start of the war the inspectorate consisted of Colonel [[Sylvester Churchill]], the senior IG of the army, and Colonel [[Joseph K. Mansfield]], the junior IG.  Churchill however took leave in April 1861 on account of his health and formally retired in September that year, while Mansfield was promoted to major-general and left to command troops in May.  Colonel [[Henry Lee Scott]] replaced Mansfield that same month, but when Churchill retired his position was given to Colonel [[Randolph Marcy]], father-in-law to George McClellan, in the same month.  Serving as the chief of staff to McClellan, Marcy did not formally take up his duties as senior IG until after the [[Battle of Antietam]], by which point however his association with McClellan had soured Marcy's relationship with Secretary Stanton, who sent him on inspection tours of various geographical departments.  Instead, the [[de facto]] leader of the inspectorate was whoever was the IG in charge of the Washington office, which was Colonel [[Delos Sacket]] between January 1863 and March 1864, and Colonel [[James Allen Hardie]] for the remainder of the war.<ref name="Newell94"/>

===Medical Department===
{{main|Medical Corps (United States Army)}}

The Army Medical Department (AMD) was rivaled only by the Quartermaster's Department in the scope and complexity of its responsibilities: caring for sick and wounded soldiers, operating [[field hospital|field]] and [[general hospital]]s, and acquiring and distributing medicine, medical equipment, hospital food and similar supplies.  Functions such as [[Casualty evacuation|evacuating]] soldiers off the battlefield or constructing hospitals were handled were handled by other departments, though later in the war the AMD assumed many of these roles.  In March 1864 it was placed in charge of casualty evacuation ([[U.S. Ambulance Corps]]) and the organization and operation of [[Train (military)|medical supply trains]].  In December it was given control over the construction and equipping of military hospitals, and of [[hospital train]]s and [[hospital ship]]s in February 1865.  Other responsibilities assumed during the war included care for disabled veterans and their families, prisoners of war, refugees and freed slaves; maintaining medical records of the dead and wounded; and preparing a medical and surgical history of the war. The AMD started out the war staffed by a conservative and inflexible leadership which negatively impacted its functioning, but would eventually be rectified by war's end.<ref name="Newell163">Newell & Shrader, p. 163–164</ref>

{|class="wikitable" style="float: right" 
! style="text-align:l center; background:#acc;" |Position
! style="text-align:l center; background:#acc;" |1862
! style="text-align:l center; background:#acc;" |1863
! style="text-align:l center; background:#acc;" |1864
! style="text-align:l center; background:#acc;" |1865
|-
|+Regular army medical personnel<ref>Newell & Shrader, p. 166</ref>
|-
|Surgeon General ([[Brigadier General (United States)|BG]])
|1
|1
|1
|1
|-
|Assistant Surgeon General ([[Colonel (United States)|COL]])
|1
|1
|1
|1
|-
|Medical Inspector General (COL)
|1
|1
|1
|1
|-
|Medical Inspector ([[Lieutenant Colonel (United States)|LTC]])
|8
|16
|16
|16
|-
|Surgeon ([[Major (United States)|MAJ]])
|50
|50
|50
|50
|-
|Assistant Surgeon ([[Captain (United States O-3)|CPT]])
|14
|5
|3
|
|-
|Assistant Surgeon ([[First lieutenant#United States|1LT]])
|100
|109
|111
|114
|-
|Medical Storekeeper
|6
|6
|6
|6
|-
|Medical Cadet
|70
|70
|70
|70
|-
|[[Hospital Steward]]
|201
|471
|650
|931
|-
|}

In April 1861 the AMD was the largest of the staff departments in the regular army: a [[Surgeon General of the United States Army|Surgeon General]] (with the rank of colonel), thirty surgeons, eighty-three assistant surgeons, and fifty-nine [[Hospital Steward]]s.  However this number was barely adequate to meet the needs of the army in peacetime, and in May 1861 an additional ten surgeons and twenty assistant surgeons were added to cover the new regular army regiments being raised.  Later that year in August, Congress authorized the appointment of fifty medical [[cadet]]s to be chosen from young men with a liberal education and prior medical experience.  They had the rank and pay of West Point cadets and were to act as [[ambulance attendant]]s in the field and assistants in general hospitals.<ref name="Newell166">Newell & Shrader, p. 168–177</ref>

In April 1862, Congress authorized a substantial reorganization of the AMD.  Beyond promoting the surgeon general to brigadier general and adding additional staff, one of the most controversial was the introduction of medical inspectors, as a number of these were appointed by Secretary Stanton for "political" purposes.  Charged with supervising all aspects of sanitary conditions within the army, their purview included the inspection of quarters, camps, hospitals and transports; their duties were later expanded to include issuing certificates of [[Military discharge|discharge]] for reasons of disability.  Congress also gave the surgeon general the authority to hire as many hospital stewards as necessary, and a month later they authorized the addition of six trained [[apothecaries]] and [[druggists]] as medical storekeepers.<ref name="Newell166"/>

Most regular army medical officers served in staff positions, whether at the office in Washington or out in the field as regimental surgeons, [[attending physician]]s in general hospitals, medical purveyors who ran medical supply depots and laboratories, or as the medical director of a division, corps, field army or military department.  Medical directors oversaw the operation of field hospitals and the associate medical personnel, field sanitation and medical supply within their command.  However, there was no statutory basis for their assignment, and it wasn't until February 1865 when Congress bowed to pressure and provided for officers serving in these capacities to receive rank, pay and emoluments appropriate to their responsibilities.<ref name="Newell166"/>

Added to the relatively small number of regular army medical personnel were a further 546 surgeons and assistant surgeons volunteers, appointed by the president to supplement regular army personnel in staff positions; another 5,532 civilian doctors employed under contract (mainly in general hospitals) as acting assistant surgeons; a small number of medical officers of the [[Veteran Reserve Corps]]; and the thousands of regimental surgeons and assistant surgeons appointed to the volunteer regiments by their respective state governors.  Thousands more civilians were employed by the AMD as nurses, clerks, hospital attendants, laborers, etc.  The AMD was further augmented by a number of private and semi-official philanthropic organizations, foremost among which was the [[United States Sanitary Commission]] (USCC).<ref name="Newell166"/>

The chaotic aftermath of the first Battle of Bull Run – no coordination between field hospitals and casualty evacuation, regimental surgeons refusing to treat soldiers from other units, and the few ambulance drivers robbing their charges or fleeing – exemplified the inadequacies of pre-war planning and preparations.  Burdened with an aged and conservative leadership, it took the injection of more enlightened leaders to make the necessary reforms for the AMD to meet these new challenges.  By the war's end, the AMD had implemented a better method of evacuating battlefield casualties to field hospitals and general hospitals, established laboratories to test and certify drugs and other medicines, identified reliable sources of supply and implemented effective contracting procedures, and increased the number of medical personnel to see to the needs of over a million men under arms.<ref name="Newell192">Newell & Shrader, p. 188–192</ref>

Some challenges remained however, against which only small progress was made.  Although improved [[field sanitation]] reduced disease rates and some advances like the use of [[chloroform]] proved helpful, a lack of [[aseptic surgery]] or general understanding of the [[germ theory]] led to many deaths from disease, [[Shock (circulatory)|shock]] or [[secondary infection]].  [[Psychological trauma]] was not well understood and the average soldier made due with an inadequate diet for maintaining their health.  The AMD's reliance on the Quartermaster and Subsistence departments for transportation and rations respectively left these subject to interdepartmental rivalry until late in the war, and personal conflict between military commanders and their supporting medical personnel could lead to problematic health outcomes.  Despite these faults, AMD personnel did their best to alleviate the suffering of their fellow soldiers and laid the groundwork for future improvement.<ref name="Newell192"/>

;Leadership
The Surgeon General at the start of the war was Colonel [[Thomas Lawson (military physician)|Thomas Lawson]], who at 97 years was on his deathbed and his duties were being carried out Major Robert C. Wood, one of his assistants.  When he passed in May 1861 Lawson was succeeded by [[Clement Finley]], another old soldier who was characterized by contemporaries as "utterly ossified and useless".  Finley was slow to act, failed to reform the AMD to address the needs of the war, and particularly opposed to the use of female nurses.  He was forced to retire by Secretary Stanton in April 1862 and replaced with [[William A. Hammond]], who immediately went about reorganizing the AMD, eliminating [[red tape]] and promoting competent young men to positions of authority.  His strong independent streak also earned the enmity of Secretary Stanton, who in September 1863 sent him on an extended tour of the western theater and made Colonel [[Joseph Barnes (American physician)|Joseph Barnes]] the acting Surgeon General.  When Hammond was arrested, court-martialed and dismissed in August 1864, Barnes was promoted to fill his position.  Barnes remained the Surgeon General until after the war's end and succeeded in continuing Hammond's reforms by maintaining an excellent relationship with Secretary Stanton.<ref>Newell & Shrader, p. 164–166</ref>

===Ordnance Department===
{{main|United States Army Ordnance Corps}}
The principal mission of the Ordnance Department (ORDD) during the Civil War was the development, procurement, storage, distribution and repair of all army [[List of weapons in the American Civil War|ordnance]] and ordnance-related equipment such as [[limbers and caissons]] and accoutrements.  It was also responsible for the procurement of horses to pull artillery until June 1861 when the Quartermaster Department took over that job.  The department faced challenges during the war, particularly during the early months as it struggled to arm the vastly expanded Union army whilst traitorous forces seized control of a number of arsenals and depots.  Eventually it was able to resolve many of these challenges and succeeded in providing thousands of [[field artillery]] pieces and millions of [[small arms]] for the Union army.<ref name="Eicher64"/><ref>Newell & Shrader, page 119</ref><ref name="USAL200">United States Army Logistics (1997), pages 199–200</ref>

When the Civil War began the Ordnance Department was commanded by a Chief of Ordnance and authorized forty officers, many in command of the army's arsenals and depots; fifteen ORDD military storekeepers; seventy [[ordnance sergeant]]s, often placed in supervisory roles including command of some depots and arsenals; and four hundred enlisted men, most of whom were employed as technicians at the armories and arsenals.  Hundreds of civilians were also employed, not only as clerks and laborers but also technicians and supervisors.  There were also [[Armed-forces artificer|artificiers]] on the rolls of the army's artillery regiments who were responsible for the maintenance of weapons within their regiments.<ref name="Newell127">Newell & Shrader, p. 122-127</ref>

Even in peacetime the size of the ORDD was insufficient, as fifty-six officers alone would've been required to bring the arsenals to their full authorized strength, and it proved inadequate once the war began.  In August 1861 Congress increased the authorized number of officers to forty-five: the Chief of Ordnance (brigadier general), two colonels, two lieutenant colonels, four majors, twelve captains, twelve first lieutenants, and twelve second lieutenants.  This still was not enough, and so in March 1863 an additional lieutenant colonel, two majors, eight captains and eight first lieutenants were added, bringing the authorized strength to sixty-four officers where it would remain for the rest of the war.  The number of ordnance sergeants and enlisted personnel were similarly increased on a yearly basis, until by 1865 they numbered 163 and 560 respectively, and the civilian staff was likewise increased.<ref name="Newell127"/>

In the field, each regiment was authorized an ordnance officer (to be chosen from among the unit's lieutenants) who, assisted by an ordnance sergeant, saw to the requisition and issuing of arms to the troops and management of the regimental ammunition [[Train (military)|train]]. For brigades and higher echelons of command, an ordnance officer was authorized to serve on the unit's staff with similar responsibilities. However unlike with the other supply departments, the ordnance department did not commission any volunteer officers to this role, instead relying on ORRD officers or (at division level and below) relying on regular officers filling the role as acting ordnance officers or combining the role with the assigned quartermaster.<ref name="Newell127"/>

The ORDD maintained a number of arsenals, armories and depots, where the majority of the army's arms, ammunition and other ordnance-related supplies were manufactured and/or stored. A number were seized before or at the war's outbreak, but more were created after fighting began and existing ones were expanded. By the middle of the war, the largest arsenals employed between one and two thousand civilians each. A substantial number of these employees were women and children, partly because they could be paid less than adult male workers, their small hands were thought to be better suited to assembling [[Cartridge (firearms)|cartridges]], and women were believed to be more safety-oriented.  Their line of work was dangerous for obvious reasons, and a number died in accidental explosions during the war. In the single-worst accident of the war, the [[Allegheny Arsenal#Explosion|explosion at the Allegheny Arsenal]], 70 of the 78 victims were women and girls.<ref name="Newell127"/>

{|class="wikitable" style="display: inline-table;" 
! style="text-align:center; background:#acc;" |Name
! style="text-align:l center; background:#acc;" |Location
! style="text-align:l center; background:#acc;" |Established
! style="text-align:center; background:#acc;" |Notes
|-
|+United States Arsenals, Armories and Depots<ref name="Eicher64">Eicher, p. 63-64</ref><ref>Beers, H. P., Munden, K. W. (1998). The Union: A Guide to Federal Archives Relating to the Civil War. Washington: National Archives and Records Administration. p. 284-287</ref><ref>Newell & Shrader, p. 124</ref>
|-
|[[Springfield Armory]]
|[[Springfield, MA]]
|1794
|Principal US Army armory
|-
|[[Harpers Ferry Armory]]
|[[Harper's Ferry, WV|Harper's Ferry, VA]]
|1796
|Destroyed April 1861, seized by [[Confederate States Army|CSA]] 
|-
|[[Allegheny Arsenal]]
|[[Pittsburgh, PA]]
|1814
| 
|-
|[[Watervliet Arsenal]]
|[[Watervliet, NY]]
|1814
| 
|-
|[[Champlain Arsenal]]
|[[Vergennes, VT]]
|1816
|Discontinued 1855, reestablished 1861
|-
|[[Frankford Arsenal]]
|[[Philadelphia|Philadelphia, PA]]
|1816
|
|-
|[[Rome Arsenal]]
|[[Rome, NY]]
|1816
|
|-
|[[Bellona Arsenal]]
|[[Richmond, VA]]
|1816
|Discontinued 1835, seized by Virginia April 1861
|-
|[[Washington Arsenal]]
|[[Washington, D.C.]]
|1816
|
|-
|[[Watertown Arsenal]]
|[[Watertown, MA]]
|1816
|
|-
|[[Pikesville Arsenal]]
|[[Pikesville, MD]]
|1819
|
|-
|[[Augusta Arsenal]]
|[[Augusta, GA]]
|1826
|Seized by Georgia militia January 1861
|-
|[[Baton Rouge Arsenal]]
|[[Baton Rouge, LA]]
|1826
|Seized by Louisiana militia January 1861
|-
|[[Kennebec Arsenal]]
|[[Augusta, ME]]
|1827
|
|-
|[[St. Louis Arsenal]]
|[[St. Louis, MO]]
|1827
|
|-
|[[Mount Vernon Arsenal]]
|[[Mount Vernon, AL]]
|1829
|Seized by Alabama militia January 1861
|-
|[[Detroit Arsenal (Dearborn)|Detroit Arsenal]]
|[[Dearborn, MI]]
|1832
|
|-
|[[Apalachicola Arsenal]]
|[[Apalachicola, FL]]
|1833
|Seized by Florida militia January 1861
|-
|[[Governors Island#Mid-19th century and Civil War|New York Arsenal]]
|[[Governors Island]], [[New York (state)|NY]]
|1836
|
|-
|[[Fayetteville Arsenal]]
|[[Fayetteville, NC]]
|1836
|Seized by North Carolina militia April 1861
|-
|[[Little Rock Arsenal]]
|[[Little Rock, AR]]
|1837
|Seized by Arkansas authorities February 1861
|-
|[[Fort Monroe|Fort Monroe Arsenal]]
|[[Old Point Comfort]], [[Virginia|VA]]
|1838
|
|-
|[[Charleston Arsenal]]
|[[Charleston, SC]]
|1841
|Seized by South Carolina militia December 1860
|-
|[[Fort Leavenworth|Leavenworth Arsenal]]
|[[Leavenworth, KS]]
|1847
|
|-
|[[Benicia Arsenal]]
|[[Benicia, CA]]
|1851
|
|-
|San Antonio Arsenal
|[[San Antonio, TX]]
|1855
|Seized by Texas militia February 1861
|-
|[[Fort Vancouver National Historic Site|Vancouver Arsenal]]
|[[Fort Vancouver]], [[Washington (state)|WA]]
|1859
|
|-
|[[Fort Union National Monument|Fort Union Arsenal]]
|Fort Union, [[New Mexico|NM]]
|1860
|
|-
|Louisville Depot
|[[Louisville, KY]]
|1861
|
|-
|Nashville Depot
|[[Nashville, TN]]
|1862
|
|-
|[[Columbus Arsenal]]
|[[Columbus, OH]]
|1863
|
|-
|Indianapolis Arsenal
|[[Indianapolis, IN]]
|1863
|
|-
|[[Rock Island Arsenal]]
|[[Rock Island, IL]]
|1863
|
|-
|}

The ORDD faced an immediate crisis when the war began as it was suddenly responsible for arming the rapidly-expanding number of troops being brought into Federal service. This job was made more difficult by actions taken by Secretary of War [[John B. Floyd]] before the war, when he ordered the transfer of large numbers of arms from Northern to Southern arsenals and the sale of Federal arms to various Southern states.<ref name="Newell135">Newell & Shrader, pages 127–135</ref>  When the Southern states did seize the arsenals within their territory, in addition to the gun-making equipment at Harper's Ferry they were able to acquire about 159,000 small arms, 429 cannons, and 4.5 million rounds of small arms ammunition.<ref name="USAL200"/>  ORDD was forced to make up the immediate shortfall by contracting with private companies or purchasing from European powers; many weapons bought under contract proved to be inferior to government standards or sold at inflated prices, while European governments were happy to get rid of their obsolete weapons.  Eventually the fraud and corruption was brought under control and ORDD was able to bring its arsenals' productions levels up to where they could meet the army's need. This can be seen with the rapid expansion of the Springfield Armory, which before the war averaged 800 muskets a month but by January 1863 was producing 24,000 muskets and rifles a month.<ref name="Newell135"/>

A more persistent issue faced by ORDD were efforts by members of Congress, the general public, and even President Lincoln to get them to adopt many new military technologies, particularly [[breechloader|breech-loading]] and [[repeating rifle]]s like the [[Spencer repeating rifle|Spencer]] and [[Henry rifle]].  The department's senior leadership was unwilling to wholeheartedly embrace this technology without extensive field testing, and worried over delays from retooling manufacturing equipment and other logistical concerns that went with their adoption.  Nevertheless, a limited number of these weapons were purchased and distributed to troops in the field, and trials were undertaken to determine which one would become the army's standard rifle for general use, although these weren't completed until well after the war ended.<ref name="Newell135"/>

After the war ORDD came under harsh criticisms, particularly over their conservatism in regards to new technology.  However it did meet the challenge of equipping the Union army with many modern weapons and other materiel.  From the beginning of the war to the end, Federal arsenals produced 7,892 cannons with over six million artillery [[Shell (projectile)|shot and shell]] and six million pounds of [[grapeshot]] and [[canister shot]]; more than 4 million small arms with over a billion rounds of small arms ammunition; over 13,000 tons of gunpowder and 45,000 tons of lead; and nearly 3 million complete sets of infantry and cavalry accoutrements and horse equipment.<ref name="Eicher64"/><ref name="Newell135"/>

;Leadership
[[Henry K. Craig]] was the Chief of Ordnance when the Civil War began, having served in that position since 1851.  Craig received much of the blame for the poor state of affairs at the time, and angered many special interests by resisting the purchase of new and untested weapons in favor of increasing arsenal production and limiting purchases to reputable domestic and international sources.  His obstinate behavior saw Craig relieved and replaced with [[James Wolfe Ripley]] on April 23, 1861.  However Ripley was similarly resistant to these same private contractors and their Congressional backers, particularly with adopting breech-loading rifles, and so was forced to retire on September 15, 1863.  His replacement, [[George D. Ramsay]], was more open to the new weaponry but did not have the confidence of Secretary Stanton, who inserted Captain George T Balch into Ramsay's headquarters to "call the shots".  Ramsay endured this situation until forced to retire on September 12, 1864. [[Alexander Brydie Dyer]] took over as Chief of Ordnance and served out the remainder of the war heading the department. While resistant to the lobbyists like his predecessors, Dyer was a more enthusiastic proponent of breech-loading and repeating rifles. He was also more bureaucratically adept and able to remain on good terms with Secretary Stanton.<ref>Newell & Shrader, pages 109–110</ref>

===Pay Department===
{{main|Finance Corps}}
The Pay Department had the responsibility of accounting for, maintaining records regarding, and disbursing of funds for payment to army personnel, including allowances and bounties, as well as settling claims against the government related to pay and allowances. It was not however responsible for payments on contracts and other obligations incurred by the Army as those were handled by the respective department. Payments to officers and soldiers was supposed to be made on a bi-monthly basis, although circumstances might see these delayed significantly (as much as by eight months in some cases).<ref name="Newell104">Newell & Shrader, pages 98–104</ref>

As originally organized the Pay Department was headed by a paymaster general with the rank of colonel, two deputy paymasters general with the rank of lieutenant colonel, and twenty-five paymasters with the rank of major. There were also a small number of civilian clerks, but no enlisted personnel assigned to the department. Cash was received directly by the paymaster general from the [[United States Department of the Treasury|Treasury Department]] and forwarded to the supervising paymaster of a given "pay district" or field headquarters. These funds were then distributed under armed guard to the officers and soldiers within the pay district. Pay districts generally coincided with the boundaries of military divisions, departments and districts, which as the army grew the number and size of pay districts grew likewise. This required the appointment of more paymasters during the course of the war and an increase in the number of civilian clerks, the latter of which reached a peak of 155 by 1864.<ref name="Newell104"/>

The rapid increase in the size of the army presented a significant challenge to the Pay Department, as the number of soldiers needed to be paid was over fifty times greater than the pre-war size.  This was particularly the case for sick and wounded soldiers who were separated from their units and so harder to located.  However while payments were occasionally delayed, it never got to the point where soldiers felt compelled to mutiny as had been done during the [[American Revolutionary War|Revolution]]. In the four years and four months of the Civil War, the Pay Department disbursed $1,029,239,000 of which $541,000 was lost due to embezzlements and other causes, at an expense of $6,429,600.<ref name="Newell104"/>

;Leadership
When the Civil War began, Colonel [[Benjamin F. Larned]] served as Paymaster General but was in poor health.  He was temporarily relieved of duty in July 1862 due to illness and would die a few months later. From July until December of that year, Major Cary H. Fry served as the acting Paymaster General, when [[Timothy Andrews (general)|Timothy Andrews]] was appointed to the position.  He would remain in that position until retiring in November 1864, when [[Benjamin Brice]] was appointed in his place and finished out the war as Paymaster General.  Both Andrews and Brice argued that the position of Paymaster General should made a brigadier general and the number and rank of subordinate paymasters similarly increased, commensurate with the type of expansion other administrative departments experienced during the war, but their recommendations were ignored.<ref name="Newell104"/>

===Provost Marshal General's Bureau===
{{main|United States Army Provost Marshal General}}
The Provost Marshal General's Bureau (PMGB) was created to oversee the apprehension of deserters, conduct [[counterespionage]], and recover stolen government property.  Originally established as an office of the AGD in September 1862, it was made an independent department in May 1863 as part of the Conscription Act of 3 March 1863.  The Conscription Act also made it responsible for the administration of the draft system, with two other responsibilities added later that year: first with the management of the [[Invalid Corps]] in April, and then the recruitment of white volunteers in May.  Intended only as temporary organization for the duration of the war the PMGB was effectively terminated in August 1866, whereupon all records, funds and responsibilities were transferred to the AGD.<ref name="Eicher58"/><ref name="Newell106">Newell & Shrader, pages 104–106</ref>

Initially consisting of a single officer, the provost marshal general (PMG) himself, eventually the bureau was authorized fourteen additional officers split between several branches. However, a mix of officers from the regulars, volunteers, and Invalid Corps were also detailed to the PMGB to fulfill a number of rolls. Each congressional district was appointed a provost marshal who served on a "board of enrollment". The board included two other persons (one of whom was to be a licensed physician) and was charged with overseeing the enrollment of men for the draft. An enrolling officer could also be appointed per subdistrict (town, township or ward) on a temporary basis, as could special agents tasked with apprehending deserters.  Additionally, all provost marshals and special agents were empowered to arrest any stragglers and send them to the nearest military post. By November 1864 the PMGB (not counting the Invalid Corps) included 4,716 officers and employees.<ref name="Newell106"/>

In the aggregate, the PMGB was successful in the enrollment and maintenance of sufficient manpower for the Union army.  Over one million men were brought into the Union army at a cost of $9.84 per man (versus $34.01 per man prior to the bureau's formation) and the arrest and return to duty of over 76,500 deserters. The bureau was also able to raise $26 million to fully fund its enrollment and draft duties.<ref name="Newell106"/>

;Leadership
When originally created as an office of the AGD, Colonel Simeon Draper was named the Provost Marshal General, which he held from October 1862 to March 1863.  However, the PMGB did not live up to expectations under Draper's leadership.  When it was made an independent department he was replaced with [[James Barnet Fry]], who served as the PMG until the bureau's dissolution.<ref name="Newell106"/>

===Quartermaster's Department===
{{main|Quartermaster Corps (United States Army)}}
The Quartermaster's Department (QMD) was the most important and extensive department of the Union army, not least because it provided transportation services to the entire army, including the other supply departments.  The QMD was responsible for the procurement, storage and distribution of supplies not already covered by another supply department, including various [[equipage]] (clothing, tents, stoves, etc.), horses and mules ([[United States Army Remount Service#Early history|Cavalry Bureau]]), [[forage]] and [[fuel]], and non-Ordnance vehicles including wagons, ambulances and [[traveling forge]]s.  Other assumed responsibilities included the acquisition, construction and maintenance of various military structures such as barracks, hospitals, wharves, storehouses, etc.; the charter, purchase and maintenance of all [[riverine]] and [[ocean-going vessel]]s used by the army and the [[Western Gunboat Flotilla]]; the construction, maintenance and management of all military railroad transportation ([[United States Military Railroad]]); the construction, maintenance and management of military telegraph lines ([[U.S. Military Telegraph Corps]]); management of all [[Train (military)|wagon trains]] in the field; the collection and burial of the dead and maintenance of [[United States National Cemetery System|national cemeteries]]; and any expenses associated with army movement and operations that did not fall under another department's purview.<ref name="Newell139">Newell & Shrader, page 139</ref><ref name="Eicher61">Eicher, pages 60–61</ref>

The QMD at the start of the war consisted of just thirty-seven officers, seven military storekeepers, and thirteen civilian clerks at the office of the Quartermaster-General (QMG), a situation which was considered understaffed even for peacetime requirements. Within a month of the conflict's start, Congress passed an act to raise the number of officers to forty-nine, and again several months later it was raised to seventy-six, adding an assistant quartermaster-general (colonel) and additional numbers of deputy quartermaster-generals (lieutenant colonel), quartermasters (major) and assistant quartermasters (captain) to support the QMG (brigadier-general). Although a substantial increase, this was not enough to meet the needs of the QMD, and so more than nine hundred assistant quartermasters of volunteers were commissioned and a large number of regular and volunteer officers were detailed to serve as acting quartermasters during the war. Congress also authorized the number of storekeepers increased to twelve and the hiring of additional clerks and other civilian workers for the office (including women), which would grow to over 200 by 1863 and close to 600 by the war's end. To this were added the many civilians working at the quartermaster depots or with quartermasters in the field. Many of these workers were rowdy and difficult to manage, especially before Congress made QMD employees subject to military law and discipline. One exception were Black workers who proved more reliable and whom Quartermaster-General Meigs considered a great aid; by 1864 the QMD was largely reliant on them to fulfill various unskilled positions.<ref name="Newell142">Newell & Shrader, pages 142–151</ref>

Officers of the QMD were assigned as commanders of the various quartermaster depots or to the staff of various field units (with the exception of regiments, whose quartermaster personnel were selected from among its own officers and NCOs).  Depot commanders were responsible for the acquisition, storage and distribution of supplies and the disbursement of funds for transportation and other services. Supplies could be manufactured within the depot or purchased from commercial interests, usually as part of a low-bid contract but in an emergency on the open market. In the first three years of the war depot commanders themselves were responsible for managing these contracts, but by July 1864 a more centralized system requiring approval from the QMG's office had been implemented to improve accountability. Based on unit quartermasters' requests, supplies would be shipped to advanced depots or railheads, where the unit quartermasters arraigned to have them picked up and issued to the unit.<ref name="Newell142"/><ref name="USAL202">United States Army Logistics, pages 202–204</ref>

The principal depots of the QMD were located in [[Cincinnati]], [[Milwaukee]], [[New York City|New York]], [[Philadelphia]], [[Quincy, Illinois]], [[Steubenville, Ohio]], [[St. Louis]], and [[Washington, D.C.]],<ref name="Eicher61"/> with other major depots located in [[Baltimore]], [[Chicago]], [[Louisville, Kentucky|Louisville]], [[New Orleans]], and [[San Francisco]].<ref name="USAL202"/> New York, Philadelphia, and Washington were the primary depots supporting Union armies in the eastern theater, with Cincinnati, St. Louis, and Louisville the primary support depots in the western theater. Many advanced and temporary depots were established as needed, including at [[Alexandria, Virginia]], Fort Monroe, [[City Point, Virginia]], and Nashville, which could become as large and busy as any general depot.  However, despite these depots being responsible for thousands of soldiers and millions of dollars in supplies, many of their commanders were only captains.  Congress approved in July 1864 the appointment of ten depot commanders to the rank of colonel, while other commanders either received a volunteer commission or brevet rank of brigadier general for as long as they remained at their depot.<ref name="Newell142"/>

In the early months of the conflict, the QMD struggled to clothe, equip and transport the rapidly-growing Union army, especially as fraud, war profiteering and political interference was rampant.  Under the able leadership of Quartermaster-General Meigs and legislation passed by Congress, this corruption was quickly brought under control and most quartermasters (with notable exceptions such as [[Justus McKinstry]]) proved to be able and law-abiding.<ref name="Newell151">Newell & Shrader, pages 151–161</ref> Undoubtedly this was due in part to the requirement that quartermasters file a [[Bond (finance)|bond]] worth $10,000 that made them personally liable for their supplies. The exception to this was when the supplies were destroyed due to natural causes or to prevent them falling into enemy hands, a situation which perversely caused celebration among some quartermasters.<ref>Hess, E. J. (2017). Civil War Logistics: A Study of Military Transportation. United States: LSU Press. page 22</ref>  While there were inevitably mistakes and other mishaps, the Union army was rarely deprived of the supplies and services provided by the QMD. Although the scope and scale of the Civil War was beyond any prewar planning, the professional competence of the department allowed it to quickly meet every challenge.  It also exploited emerging technologies like railroads and steamboats with expertise to support the Union army like never before at a strategic and operational level.<ref name="Newell151"/>

Of the $1.8 billion spent by the Federal government during the war, over a billion of that was distributed by the Quartermaster Department.<ref>Hess (2017), page 30</ref>  Among the staggering number of supplies and services acquired by the QMD include approximately a million horses and half a million mules; the movement by rail of over 1.2 million troops; 590 ocean-going vessels under charter or owned outright providing over 190,000 tons of shipping, with another 599 riverine vessels; over 1.6 million tons of coal and 500,000 [[Cord (unit)|cords]] of wood; over 22 million [[bushel]]s of corn, 78 million of oat, 1.5 million tons of hay and 21,000 tons of straw and other fodder; more than $23 million for the rental, construction and maintenance of army property; and over 51,000 standard army wagons and 5,300 ambulances.<ref name="Newell151"/>

;Leadership
The Quartermaster General at the start of the war was [[Joseph E. Johnston]], who resigned shortly after on April 22, 1861, to join the Confederate army. Major Ebenezer S. Sibly served as acting QMG until [[Montgomery C. Meigs]] was appointed and took up his new duties on June 13, 1861. Considered one of the most effective leaders to serve in the Union army, Meigs oversaw the expansion of the QMD to meet the demands of the war and continued to lead it well after its end. Meigs was also a [[hands-on management|hands-on manager]] and from August 1863 to January 1864 he was busy handling logistical matters in the western theatre. During his absence, Colonel [[Charles Thomas (1797–1878)|Charles Thomas]] served as acting QMG in Washington.<ref>Newell & Shrader, page 140</ref>

===Signal Corps===
{{main|Signal Corps in the American Civil War}}
The creation of a [[Signal Corps (United States Army)|Signal Corps]] for the US Army was the result of [[Albert James Myer]], an army surgeon who had developed a system of [[military signals]] based on [[sign language]] known as [[Wigwag (flag signals)|wigwag]].  Myer was appointed to the rank of major and to lead the Signal Corps (albeit as its only officer) effective June 27, 1860.  During the early years of the Civil War the Signal Corps did not have any personnel other than Myer appointed to it.  Instead, officers and enlisted men were sent from other units to [[Fort Monroe]] to learn his system and in turn teach others.  Myer continued to campaign for a more formal and permanent Signal Corps, which was finally granted by Congress on March 3, 1863.  However, a dispute between the Signal Corps and the [[U.S. Military Telegraph Corps]] over who controlled [[electrical telegraph]]y led Secretary Stanton to replace Myer with Maj. William Nicodemus in November of that year.  After an inadvertent release of confidential information, Nicodemus was in turn replaced by Colonel Bejamin Fisher, who would remain the Corps' commander until the end of the war.  The Signal Corps proved instrumental in coordinating the actions of the Union army during the Civil War and afterwards Congress appointed Myers to once again lead it in 1866.<ref name="Newell303">Newell & Shrader, pages 292–303</ref>

===Subsistence Department===
The mission of the Subsistence Department was the purchase, storage and distribution of [[Foods of the American Civil War|rations]] and related items in a timely manner. It was the smallest of the four supply departments, and even as the army grew to encompass over a million soldiers the department itself barely expanded in size.  Yet it was able to meet its mission to such an extent that President Lincoln once remarked to an officer "Your department we scarcely hear of; it is like a well-regulated stomach, works so smoothly we are not conscious of having it."<ref name="Newell111">Newell & Shrader, pages 109–111</ref>

The authorized strength of the department at the war's start was a Commissary General of Subsistence (CGS) with the rank of colonel, an assistant CGS with the rank of lieutenant colonel, and ten commissaries of subsistence (CS), two with the rank of major and the rest captains. Those not assigned to work at the office of the CGS in Washington were in charge of one of the subsistence depots or purchasing offices, or assigned to the staff of one of the military departments. Although there were no enlisted personnel in the department (all commissary positions at the regimental level being fulfilled by members of the regiment), a small civilian staff of clerks and laborers was assigned to the department.<ref name="Newell111"/>

To meet the needs of feeding the rapidly-expanding Union army, Congress authorized a CS with the rank of captain to be assigned to each brigade in July 1861, and in August 1861 the department was expanded with twelve additional officers, four majors and eight captains. A year later when army corps were officially created a CS with the rank of lieutenant colonel was authorized to serve on their staff, and in February 1863 the department was further expanded when the CGS was promoted to brigadier general, a second assistant CGS was added with the rank of colonel, and two additional majors were authorized.  Eventually in March 1865 Congress formally recognized wartime requirements by authorizing a chief CS with the rank of colonel for each field army, military department and division, and principle subsistence depot; an assistant CS with the rank of colonel assigned to Washington; up to six CS with the rank of lieutenant colonel to serve as inspectors or special duty assignment; a chief CS with the rank of lieutenant colonel for each army corps; and a CS with the rank of major for each division.<ref name="Newell111"/>

The need to fill CS positions among the field units primarily came from volunteer officers or regular officers detailed to the duty, and by the end of the war there were 535 commissaries of subsistence of volunteers, bringing the total complement of officers in the department to 564.<ref name="Newell111"/> Although educating them in the principles of their duty was a constant problem, it was a minor one eventually fixed with time and experience, and those who could not meet the standards of the department were relieved of duty.<ref name="Newell118"/>

During the war the principle subsistence depots and purchasing offices were located in Baltimore, [[Boston]], Chicago, Cincinnati, Louisville, Philadelphia, St. Louis, San Francisco and Washington, D.C.  Depot commissaries, assisted by civilian clerks and laborers, received purchases in bulk at these locations and repackaged them for shipment to armies in the field.  The actual transportation of rations was handled by the Quartermaster Department, requiring close cooperation between the two.  Major beef depots were also established in Alexandria, Virginia, Louisville and Washington. During the war the department developed a highly effective system of base, advanced, and temporary depots, and mobile beef herds which followed behind Union forces in the field.<ref name="Newell118">Newell & Shrader, pages 112–118</ref><ref name="USAL202"/>

The success of the Subsistence Department in meeting the challenges of the war was noted by Secretary Stanton, who observed in 1865 that no operation conducted by the Union army failed on account of the department being unable to meet its obligations.  In total, the department purchased over $361 million in foodstuff and miscellaneous subsistence items from July 1, 1861, to June 30, 1865.  The vast quantities of items managed by the department included over 504 million pounds of hardtack, 223 million pounds of bacon, 200 million pounds of brown sugar, 106 million pounds of fresh beef, 64 million pounds of roasted coffee and more than 322,000 live beef cattle.<ref name="Newell118"/>

;Leadership
At the Civil War's start, the CGS was [[George Gibson (Commissary General)|George Gibson]]. Gibson, who at eighty-six was the oldest serving officer in the army, had been in this position since the department was first created in April 1818 and as such was responsible for establishing its procurement and distribution methods. When he died on September 29, 1861, he was succeeded by his deputy, [[Joseph Pannell Taylor]]. Taylor oversaw the department's expansion during the most eventful years of its history and served until his death on June 29, 1864.  The senior assistant CGS [[Amos Beebe Eaton]] was promoted to the position upon Taylor's death and served as CGS for the rest of the war.<ref name="Newell111"/>

==Military tactics==
The [[military tactics|tactics]] of the Union army, as with their Confederate opponents, was derived from [[early modern warfare|traditions]] developed in Europe around the use of [[smoothbore musket]]s: soldiers marching shoulder-to-shoulder in [[Line (formation)|lines]], [[Column (formation)|columns]] and other formations in order to deliver [[volley fire]] on the enemy.  The most notable development though was the widespread use of [[rifled musket]]s, which had an effective range of 500 yards versus the smoothbore's 100 yards.  This led to predictions the defense would have the advantage over an attacker and render such linear tactics obsolete, which many contemporaries and early historians echoed.  More recently, historians have questioned this narrative and argued based on research that most combat still took place at the range of smoothbore muskets and casualty rates were little different from during the [[Napoleonic Wars]].  Instead they assert these tactics still remained relevant during the Civil War.<ref>{{cite book|author=Earl J. Hess|title=Civil War Infantry Tactics: Training, Combat, and Small-Unit Effectiveness|url=https://books.google.com/books?id=o1njBgAAQBAJ&pg=PG1|year=2015|publisher=LSU Press|page=xi–xxi|isbn=9780807159385}}</ref>

In the first stage of an attack, preparatory fire would be carried out by [[Field artillery in the American Civil War|field artillery]] and [[skirmishers]]. When possible a [[flanking maneuver]] was preferred, but if necessary a [[frontal assault]] was conducted, with [[feint]]s to draw off the enemy's attention. Successive lines of [[Infantry in the American Civil War|infantry]] would advance on the enemy at a walking pace until the first line got to within 200 yards or less, whereupon (ideally) they broke into a charge to overrun the enemy's position, stopping only once to fire a volley. If successful the first line would regroup in place as the succeeding lines pass through to attack the next position; if they became bogged down or forced to retreat, the next line would pass through to continue the attack.<ref name=Griffith59>{{cite book|author=Paddy Griffith|title=Battle in the Civil War: Generalship and Tactics in the American Civil War 1861–65|year=2021|publisher=Amazon Digital Services LLC – KDP Print US|pages=46–59|isbn=9798534453355}}</ref> More likely, the attackers stopped within 100 yards of the enemy and begin exchanging fire with them until using up their ammunition and either be driven off or press home with a [[bayonet charge]].<ref>Griffith (2021), pages 76-81</ref>

[[Fieldworks]] were used extensively on the defensive thanks to the teachings of [[Dennis Hart Mahan]] at West Point. Even when not conducting a siege, such defensive fortifications would be constructed if time allowed. Examples included [[rifle pit]]s, [[abatis]]es, [[wire obstacle]]s, [[land mines]], and [[palisade]]s. Truly impressive [[trench warfare|trench systems]] could be constructed thanks to the widespread use of Black laborers.<ref>Griffith (2021), pages 70–72</ref>  If field fortifications were not available, the main defensive line would be formed around a strong terrain feature (stone wall, [[Embankment (earthworks)|embankment]], etc.) which ideally allowed for [[flanking fire]]. Supporting lines were placed behind the main line, on a hill overlooking it if possible but otherwise providing a ready reserve. [[Counter-battery fire]] would attempt to knock out the enemy's artillery while skirmishers harassed the attacker as they advanced. Once within range, the defending infantry attempted to drive off the enemy with superior firepower or, if timed right, a counter-charge of their own.<ref>Griffith (2021), page 53</ref>

Union [[Cavalry in the American Civil War|cavalry]] were rarely used in actual battle in the first years of the war, instead being parceled out on scouting and raiding missions and often at a disadvantage against their Confederate counterparts.  Under energetic commanders like [[Philip Sheridan]] however the Union cavalry grew into its own and developed tactics unique from their European counterparts. Instead of masses of [[heavy cavalry]] charging enemy infantry, a cavalry force would leave a portion of its troopers mounted while the rest dismounted to engage the enemy in a firefight. The widespread employment of [[repeating firearm]]s gave Union cavalry a particular advantage, especially when utilizing [[marching fire]]. If the firefight did not achieve success, the dismounted portion could clear any obstacles to allow the mounted portion to charge with revolvers and sabers, and if not successful the force could remount and use their mobility to attack from another direction. In this way an enemy could be [[defeat in detail|defeated in detail]] as these successive attacks forced them to spread out and allowed isolated elements to eventually be overwhelmed.<ref>Griffith (2021), pages 85–89</ref>

==Desertions and draft riots==
[[File:Anti Civil War Draft Rioters in Lexington Avenue New York 1863.jpg|thumb|250px|Rioters attacking a building during the New York anti-draft riots of 1863]]

[[Desertion]] was a major problem for both sides. The daily hardships of war, forced marches, thirst, suffocating heat, disease, delay in pay, solicitude for family, impatience at the monotony and futility of inactive service, panic on the eve of battle, the sense of [[war-weariness]], the lack of confidence in commanders, and the discouragement of defeat (especially early on for the Union army), all tended to lower the morale of the Union army and to increase desertion.<ref>Ella Lonn, ''Desertion During the Civil War'' (U of Nebraska Press, 1928)</ref><ref>Chris Walsh, "'Cowardice Weakness or Infirmity, Whichever It May Be Termed': A Shadow History of the Civil War." ''[[Civil War History]]'' (2013) 59#4 pages: 492–526.[http://muse.jhu.edu/journals/civil_war_history/v059/59.4.walsh.html Online]</ref>

In 1861 and 1862, the war was going badly for the Union army and there were, by some counts, 180,000 desertions. In 1863 and 1864, the bitterest two years of the war, the Union army suffered over 200 desertions every day, for a total of 150,000 desertions during those two years. This puts the total number of desertions from the Union army during the four years of the war at nearly 350,000. Using these numbers, 15% of Union soldiers deserted during the war. Official numbers put the number of deserters from the Union army at 200,000 for the entire war, or about 8% of Union army soldiers. Since desertion is defined as being AWOL for 30 or more days and some soldiers returned within that time period, as well as some deserters being labeled missing-in-action or vice versa, accurate counts are difficult to determine. Many historians estimate the "real" desertion rate in the Union army as between 9–12%.<ref>{{Cite web|url=https://www.encyclopediavirginia.org/Desertion_Confederate_during_the_Civil_War#start_entry|title=Desertion (Confederate) during the Civil War|website=encyclopediavirginia.org|access-date=13 October 2017}}</ref> About 1 out of 3 deserters returned to their regiments, either voluntarily or after being arrested and being sent back. Many deserters were professional "[[bounty jumper]]s" who would enlist to collect the cash bonus and then desert to do the same elsewhere. If not caught and executed, this crime could pay well.<ref>Shannon Smith Bennett, "Draft Resistance and Rioting." in Maggi M. Morehouse and Zoe Trodd, eds., ''Civil War America: A Social and Cultural History with Primary Sources'' (2013) ch 1</ref><ref>Peter Levine, "Draft evasion in the North during the Civil War, 1863–1865." ''Journal of American History'' (1981): 816–834. [http://www.oah.org/site/assets/documents/08_JAH_1981_levine.pdf online] {{webarchive|url=https://web.archive.org/web/20160304192058/http://www.oah.org/site/assets/documents/08_JAH_1981_levine.pdf |date=March 4, 2016}}</ref> While 147 deserters are known to have been executed by the Union Army during the Civil War, the majority sentenced to death were in fact reprieved including through the intervention of President Lincoln.<ref>{{cite web|url=https://scholarworks.umb.edu/cgi/viewcontent.cgi?article=1437&context=masters_theses|title=EXPENDABLE: EIGHT SOLDIERS FROM MASSACHUSETTS REGIMENTS EXECUTED FOR DESERTION DURING THE UNITED STATES CIVIL WAR pp.3-4; p.28|website=scholarworks.umb.ed |last=Ragon |first=Stephen |date=May 2017}}</ref><ref>{{cite web|url=https://www.presidency.ucsb.edu/documents/executive-order-deserters-death-sentences-remitted|title=Abraham Lincoln, Executive Order—Deserters Death Sentences Remitted, 26 February 1864 |website=The American Presidency Project |access-date=23 August 2025}}</ref><ref>{{cite web|url=https://www.essentialcivilwarcurriculum.com/desertion,-cowardice-and-punishment.html|title=Desertion, Cowardice and Punishment |website=Essential Civil War Curriculum |last=Weitz |first=Mark |access-date=23 August 2025}}</ref> {{about||further discussion|Capital punishment by the United States military#American Civil War}} 

Irish immigrants were the main participants in the famous "[[New York Draft riots]]" of 1863.<ref>Adrian Cook, ''The armies of the streets: the New York City draft riots of 1863'' (1974).</ref> Stirred up by the instigating rhetoric of Democratic politicians,<ref>{{Cite book|quote=Rioters were mostly Irish Catholic immigrants and their children. They mainly attacked the members of New York's small black population. For a year, Democratic leaders had been telling their Irish-American constituents that the wicked 'Black Republicans' were waging the war to free the slaves who would come north and take away the jobs of Irish workers. The use of black stevedores as scabs in a recent strike by Irish dockworkers made this charge seem plausible. The prospect of being drafted to fight to free the slaves made the Irish even more receptive to demogogic rhetoric.
|author-link=James M. McPherson|first=James M.|last=McPherson
|url=https://archive.org/details/drawnwithswordre00mcph|url-access=registration|date=1996
|title=Drawn with the Sword: Reflections on the American Civil War
|publisher=Oxford University Press, Inc.|location=New York
|pages=[https://archive.org/details/drawnwithswordre00mcph/page/91 91]–92|isbn=978-0-19-509679-8}}</ref> the Irish had shown the strongest support for Southern aims prior to the start of the war and had long opposed abolitionism and the free black population, regarding them as competition for jobs and blaming them for driving down wages. Alleging that the war was merely an upper-class abolitionist war to free slaves who might move north and compete for jobs and housing, the poorer classes did not welcome a draft, especially one from which a richer man could buy an exemption. The poor formed clubs that would buy exemptions for their unlucky members. As a result of the [[Enrollment Act]], rioting began in several Northern cities, the most heavily hit being New York City. A mob reported as consisting principally of Irish immigrants rioted in the summer of 1863, with the worst violence occurring in July during the [[Battle of Gettysburg]]. The mob set fire to African American churches and the [[Colored Orphan Asylum]] as well as the homes of prominent Protestant abolitionists.  A mob was reportedly repulsed from the offices of the staunchly pro-Union ''[[New York Tribune]]'' by workers firing two Gatling guns.  The principal victims of the rioting were African Americans and activists in the anti-slavery movement.  Not until victory was achieved at Gettysburg could the Union army be sent in; some units had to open fire to quell the violence and stop the rioters. Casualties were estimated as up to 1,000 killed or wounded.<ref>Iver Bernstein, ''The New York City Draft Riots: Their Significance for American Society and Politics in the Age of the Civil War'' (1990)</ref> There were a few small scale draft riots in rural areas of the Midwest and in the coal regions of Pennsylvania.<ref>Shannon M. Smith, "Teaching Civil War Union Politics: Draft Riots in the Midwest." ''OAH Magazine of History'' (2013) 27#2 pages: 33–36. [https://archive.today/20150407173123/http://maghis.oxfordjournals.org/content/27/2/33.short online]</ref><ref>Kenneth H. Wheeler, "Local Autonomy and Civil War Draft Resistance: Holmes County, Ohio." ''Civil War History.'' v.45#2 1999. pages 147+ [https://www.questia.com/PM.qst?a=o&d=5001276214 online edition]</ref>

==See also==
{{Portal|American Civil War}}
{{col-begin|width=45%}}{{col-break}}
* [[Social history of soldiers and veterans in the United States]]
*[[Grand Army of the Republic]]
*[[American Civil War Corps Badges]] 
*[[Commemoration of the American Civil War]]
*[[Irish Americans in the American Civil War]]
*[[German Americans in the American Civil War]]
*[[Hispanics in the American Civil War]]
*[[Italian Americans in the Civil War]]
*[[Native Americans in the American Civil War]]
*[[Military history of African Americans]]
*[[Uniform of the Union Army|Uniform of the Union army]]
*[[United States National Cemeteries]]
*[[National Union Party (United States)|National Union Party]], the temporary party that Lincoln led to victory in the 1864 election
*[[Army of the Frontier]]
*[[Army of the Southwest]]
{{col-break}}
*[[I Corps (Union Army)|I Corps]]
*[[II Corps (Union Army)|II Corps]]
*[[III Corps (Union Army)|III Corps]]
*[[IV Corps (Union Army)|IV Corps]]
*[[V Corps (Union Army)|V Corps]]
*[[VI Corps (Union Army)|VI Corps]]
*[[VII Corps (Union Army)|VII Corps]]
*[[VIII Corps (Union Army)|VIII Corps]]
*[[IX Corps (Union Army)|IX Corps]]
*[[X Corps (Union Army)|X Corps]]
*[[XI Corps (Union Army)|XI Corps]]
*[[XII Corps (Union Army)|XII Corps]]
*[[XIII Corps (Union Army)|XIII Corps]]
{{col-break}}
*[[XIV Corps (Union Army)|XIV Corps]]
*[[XV Corps (Union Army)|XV Corps]]
*[[XVI Corps (Union Army)|XVI Corps]]
*[[XVII Corps (Union Army)|XVII Corps]]
*[[XVIII Corps (Union Army)|XVIII Corps]]
*[[XIX Corps (Union Army)|XIX Corps]]
*[[XX Corps (Union Army)|XX Corps]]
*[[XXI Corps (Union Army)|XXI Corps]]
*[[XXII Corps (Union Army)|XXII Corps]]
*[[XXIII Corps (Union Army)|XXIII Corps]]
*[[XXIV Corps (Union Army)|XXIV Corps]]
*[[XXV Corps (Union Army)|XXV Corps]]
*[[Cavalry Corps (Union Army)|Cavalry Corps]]
{{col-end}}

==References==
'''Notes'''
{{Reflist}}

'''Bibliography'''
*Eicher, John H., and [[David J. Eicher]]. ''Civil War High Commands''. Stanford, CA: Stanford University Press, 2001. {{ISBN|0-8047-3641-3}}.
*[[Ulysses S. Grant|Grant, Ulysses S.]] [https://www.gutenberg.org/ebooks/4367 ''Personal Memoirs of U.S. Grant'']. 2 vols. Charles L. Webster & Company, 1885–86. {{ISBN|0-914427-67-9}}.
*Glatthaar, Joseph T. ''Forged in Battle: The Civil War Alliance of Black Soldiers and White Officers''. New York: Free Press, 1990. {{ISBN|978-0-02-911815-3}}.
*Hattaway, Herman, and Archer Jones. ''How the North Won: A Military History of the Civil War''. Urbana: University of Illinois Press, 1983. {{ISBN|0-252-00918-5}}.
*[[James M. McPherson|McPherson, James M.]] ''What They Fought For, 1861–1865''. Baton Rouge: Louisiana State University Press, 1994. {{ISBN|978-0-8071-1904-4}}.
*McGrath, John J.  ''The Brigade: A History, Its Organization and Employment in the US Army.'' Fort Leavenworth, KS: Combat Studies Institute, US Army Command and General Staff College, 2004.  {{ISBN|9781428910225}}
*Shrader, C. R., Newell, C. R. (2011). ''Of Duty Well and Faithfully Done: A History of the Regular Army in the Civil War.'' University of Nebraska, 2011. {{ISBN|978-0-8032-1910-6}}.
*Wagner, Margaret E., [[Gary W. Gallagher]], and Paul Finkelman. ''The Library of Congress Civil War Desk Reference''. New York: Simon & Schuster Paperbacks, Inc., 2009 edition. {{ISBN|978-1-4391-4884-6}}. First Published 2002. 
*Wilson, J. B. (1998). ''Maneuver and Firepower: The Evolution of Divisions and Separate Brigades.'' Washington, DC: Center of Military History, U.S. Army, 1998.

'''Further reading'''
*Bledsoe, Andrew S. ''Citizen-Officers: The Union and Confederate Volunteer Junior Officer Corps in the American Civil War''. Baton Rouge, Louisiana: Louisiana State University Press, 2015. {{ISBN|978-0-8071-6070-1}}.
*Canfield, Daniel T. "Opportunity Lost: Combined Operations and the Development of Union Military Strategy, April 1861 – April 1862." ''Journal of Military History'' 79.3 (2015).
*Kahn, Matthew E., and Dora L. Costa. "Cowards and Heroes: Group Loyalty in the American Civil War." ''Quarterly journal of economics'' 2 (2003): 519–548. [https://web.archive.org/web/20150114000603/http://qje.oxfordjournals.org/content/118/2/519.abstract online version]
*[[Allan Nevins|Nevins, Allan]]. ''The War for the Union''. Volume 1, ''The Improvised War 1861–1862''.  ''The War for the Union''. Volume 2, ''War Becomes Revolution 1862–1863''.  Volume 3, ''The Organized War 1863–1864''. Volume 4, ''The Organized War to Victory 1864–1865''. (Charles Scribner's Sons, 1960–71. {{ISBN|1-56852-299-1}}.)
*Prokopowicz, Gerald J. ''All for the Regiment: the Army of the Ohio, 1861–1862'' (UNC Press, 2014). [https://www.questia.com/library/1P3-218627361/all-for-the-regiment-the-army-of-the-ohio-1861-1862 online]
*Shannon, Fred A. [http://hdl.handle.net/2027/mdp.39015001813651 ''The Organization and Administration of the Union Army 1861–1865'']. 2 volumes. Gloucester, Massachusetts: P. Smith, 1965. {{OCLC|428886}}. First published 1928 by A.H. Clark Co.
*Welcher, Frank J. ''The Union Army, 1861–1865 Organization and Operations''. Vol. 1, ''The Eastern Theater''. Bloomington: Indiana University Press, 1989. {{ISBN|0-253-36453-1}}; . ''The Union Army, 1861–1865 Organization and Operations''. Volume 2, ''The Western Theater''. (1993). {{ISBN|0-253-36454-X}}.

==External links==
{{Commons category}}
*[http://www.civilwarhome.com/ethnic.htm Civil War Home: Ethnic groups in the Union Army]
*[http://www.historynet.com/who-was-the-common-soldier-of-americas-civil-war.htm "The Common Soldier", HistoryNet]
*[http://jdc.jefferson.edu/milsurgusa/ ''A Manual of Military Surgery''], by Samuel D. Gross, MD (1861), the manual used by doctors in the Union Army.
*[https://web.archive.org/web/20130605120519/http://www.civilwarsoldier.com/cws_gallery_007.htm Union Army Historical Pictures]
*[http://battleofolustee.org/uniforms/uniforms.html U.S. Civil War Era Uniforms and Accoutrements]
*[http://www2.hsp.org/collections/manuscripts/r/Rosenthal3128.html Louis N. Rosenthal lithographs], depicting over 50 Union Army camps, are available for research use at the [[Historical Society of Pennsylvania]].
*[https://archive.org/stream/officialarmyregi00unitrich#page/n3/mode/2up Official Army register of the Volunteer Force 1861; 1862; 1863; 1864; 1865]
*[http://civilwarroster.com/cw/cw-bury.htm Civil War National Cemeteries]
*[https://archive.org/details/recordoffederald00unit Christian Commission of Union Dead]
*[https://books.google.com/books?id=hUN3AAAAMAAJ Roll of Honor: Names of Soldiers who died in Defense of the Union Volumes 1–8]
*[https://books.google.com/books?id=z0Z3AAAAMAAJ Roll of Honor: Names of Soldiers who died in Defense of the Union Volumes 9–12]
*[https://archive.org/details/bub_gb_Co53AAAAMAAJ Roll of Honor: Names of Soldiers who died in Defense of the Union Volumes 13–15]
*[https://books.google.com/books?id=-m0UAAAAYAAJ Roll of Honor: Names of Soldiers who died in Defense of the Union Volumes 16–17]
*[http://search.ancestry.com/Browse/BookView.aspx?dbid=48626&iid=RollHonorXVIII-003885-1 Roll of Honor: Names of Soldiers who died in Defense of the Union Volume 18]
*[http://search.ancestry.com/Browse/BookView.aspx?dbid=48622&iid=RollHonorXIX-004346-i Roll of Honor: names of Soldiers who died in Defense of the Union Volume 19]
*[https://archive.org/stream/rollofhonornames21unit#page/n5/mode/2up Roll of Honor: Names of Soldiers who died in Defense of the Union Volumes 20–21]
*[https://archive.org/stream/rollofhonornames23unit#page/n5/mode/2up Roll of Honor: Names of Soldiers who died in Defense of the Union Volumes 22–23]
*[https://archive.org/stream/rollofhonornames27unit#page/n7/mode/2up Roll of Honor: Names of Soldiers who died in Defense of the Union Volumes 24–27]
*[https://books.google.com/books?id=dgF-AAAAMAAJ&dq=National+Cemetery+at+Vicksburg+Mississippi&pg=RA6-PA85 Roll of Honor: Names of Soldiers who died in defense of the Union Volumes XXVII]

{{American Civil War |expanded=CTCBS}}

{{authority control}}

[[Category:Union army| ]]