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{{Short description|German submarine}}
{{distinguish|British U-class submarine|Das U-Boot}}
{{Use dmy dates|date=May 2014}}
[[File:U995 2001 1 b.jpg|thumb|upright=1.25|{{GS|U-995||2}}, a typical VIIC/41 U-boat on display at the [[Laboe Naval Memorial]] near [[Kiel]], Germany]]

'''U-boats''' are [[Submarine#Military|naval submarines]] operated by Germany, especially during [[World War I]] and [[World War II]]. The term is an [[Anglicization#Loanwords|anglicized]] form of the German word {{lang|de|U-Boot}} {{IPA|de|ˈuːboːt||De-U-Boot.oga}}, a shortening of {{lang|de|Unterseeboot}} ({{lit |under-sea boat}}). [[Austro-Hungarian Navy]] submarines were also known as U-boats.

U-boats are especially known for their use in [[unrestricted submarine warfare]] in both world wars, attempting to [[Commerce raiding|disrupt merchant traffic]] towards the UK and force the UK out of the war. In [[World War I]], Germany intermittently waged unrestricted submarine warfare against the [[United Kingdom|UK]]: a first campaign in 1915 was abandoned after strong protests from the US but in February 1917 the Germans, facing deadlock on the continent, saw no other option than to resume the campaign. The renewed campaign failed to achieve its goal mainly because of the introduction of [[Convoys in World War I|convoys]]. Instead the campaign ensured final defeat as the campaign was a contributing factor to the entry of the [[United States|US]] in the First World War.{{Sfn|Blair||pp=10-19}}

In [[World War II]], [[Karl Dönitz]], supreme commander of the {{lang|de|[[Kriegsmarine]]}}'s U-boat arm ({{lang|de|[[Befehlshaber der Unterseeboote]])}}, was convinced the UK and its convoys could be defeated by new [[Wolfpack (naval tactic)|tactics]], and tried to focus on [[Convoy battles of World War II|convoy battles]].{{Sfn|Blair||pp=38-39}} Though U-boat tactics initially saw success in the [[Battle of the Atlantic]], greatly disrupting Allied shipping, improved convoy and anti-submarine tactics such as [[high-frequency direction finding]] and the [[Hedgehog (weapon)|Hedgehog anti-submarine system]] began to take a toll on the German U-boat force. This ultimately came to a head in May 1943, known as [[Black May (1943)|Black May]], in which U-boat losses began to outpace their effect on shipping.

==Early U-boats (1850–1914)==
[[File:SM U 1 800px.jpg|left|thumb|The first German submarine, the SM ''U-1. Her'' remains are on display at the [[Deutsches Museum]] in Munich.{{Sfn|Showell||p=|pp=36-37}}]]
A more advanced [[submersible]], the three-man ''[[Brandtaucher]],'' was designed by [[Wilhelm Bauer]] in 1850 and constructed by [[August Howaldt|Schweffel and Howaldt]] in [[Kiel]]. It was lost on 1 February 1851 during a test dive.{{Efn|''Brandtaucher'' ihas been salvaged and is on display at the [[Bundeswehr Military History Museum]], [[Dresden]]{{sfn|Möller|Brack|2004|p=11}}}}{{Sfn|Showell||p=23}}{{Sfn|Chaffin||p=53}}

Some 50 years later in 1903, the [[Friedrich Krupp Germaniawerft]] dockyard in Kiel completed the first fully functional German-built submarine, ''[[Russian submarine Forel|Forelle]]'',{{Sfn|Showell||p=201}} which [[Krupp]] sold to Russia during the [[Russo-Japanese War]] in April 1903.{{Sfn|Showell||p=|pp=22-29}}

At this time, the German commander of the Navy [[Alfred von Tirpitz]] was building the [[High Seas Fleet]] with which he intended to challenge the supremacy of the UK [[Royal Navy]]. He focused on expensive [[battleship]]s and there was no role for submarines in his fleet.

Only when Krupp received an order for three {{sclass|Karp|submarine|0}} U-boats from Russia, did Tirpitz order one submarine.{{Sfn|Blair||p=6}}{{Sfn|Rössler|2001|p=17}} The {{SMU|U-1|Germany|6}} was a completely redesigned ''Karp''-class and when the [[Imperial German Navy]] commissioned it on 14 December 1906,{{Sfn|Showell||p=30}} it was the last major navy to adopt submarines.{{Sfn|Blair||p=6}}

The ''U-1'' had a double hull and a single {{convert|45|cm|in|0|abbr=on}} torpedo tube. It used an [[electric motor]] powered by batteries for submerged propulsion and a [[Körting Hannover|Körting]] [[kerosene]] engine for charging the batteries and propulsion on the surface.{{Sfn|Rössler|2001|p=22}} The 50%-larger {{SMU|U-2|Germany|6}} was commissioned in 1908,{{sfn|Möller|Brack|2004|p=17}} had four 45&nbsp;cm torpedo tubes and a much larger battery capacity. But the boat was a failure due to problems with both the kerosene and electrical engines. The next two U-boats of the [[Type U 3 submarine|Type U 3]]-class, ordered on 13 August 1907, were more reliable.{{Sfn|Rössler|2001|p=22}}

[[File:SM U 11 800px.jpg|thumb|The German submarine ''U-14'', showing the kerosene vapour trail.]]In March 1907, the Germaniawerft received an order from the [[Austro-Hungarian Navy]] for two {{cvt|237|t|LT}} U-boats and in October [[Norway]] ordered a similar U-boat.

These foreign U-boats were based on an improved ''U-1'' design.{{Sfn|Rössler|2001|p=23}} Between 1908 and 1910, the German navy ordered fourteen {{cvt|500|t|LT|adj=on}} boats with four 45&nbsp;cm torpedo tubes and two reload torpedoes. These boats used a kerosene engine which was safer than [[gasoline]] and more powerful than [[steam]], but the white exhaust of the kerosene betrayed the presence of the U-boats, robbing them of their primary asset, their stealth. Diesel engines did not have that disadvantage, but a powerful and reliable diesel engine was still under development.{{Sfn|Blair||p=7}} As some equipment could not be delivered within the specified weight limits, there was some variation in the total weight of each U-boat. Usually this was solved by reducing the number of battery cells, which affected underwater performance.{{Sfn|Rössler|2001|p=25}} The last two of these U-boats, the [[Type U 17 submarine|Type U 17]], was designed to receive diesel engines but due to delays in developing a lightweight diesel engine, these U-boats were equipped with kerosene engines.{{Sfn|Rössler|2001|p=27}}

Between 1910 and 1912, twenty-three diesel U-boats were ordered{{Sfn|Blair||p=7}} when diesel engines finally became available: four {{cvt|650|t|LT|adj=on}} [[Type U 19 submarine|Type U 19]] U-boats on 20 November 1910 from [[Kaiserliche Werft Danzig|KWD]] with [[MAN SE|MAN]] engines and four similar [[Type U 23 submarine|Type U 23]] U-boats from Germaniawerft with Germaniawerft engines on 18 March 1911. These boats were larger to accommodate the diesel engines, and were equipped with {{convert|50|cm|in|0|abbr=on}} torpedo tubes. On 12 February 1912 a further four similar [[Type U 27 submarine|Type U 27]] were ordered from KWD, and although Germaniawerft experienced problems with its diesel engines, it received an order for eleven [[German Type U 31 submarine|Type U 31]] U-boats. Due to these problems, delivery of these U-boats was delayed up to eight months and ran into 1915.{{Sfn|Rössler|2001|p=28}}

At the start of World War I in 1914, Germany had 48 submarines of 13 classes in service or under construction.{{Sfn|Blair||p=7}}

=== Pre World War I Classes{{sfn|Möller|Brack|2004|pp=16-27}} ===
{| class="wikitable mw-collapsible mw-collapsed"
! colspan="8" |U-boats built by Germany for the German Navy
|-
!Type
!Nbr built
!In service
!Displacement surface
!Speed surface
!Speed submerged
!Engines surface{{Sfn|Rössler|2001|p=328}}
!Engines submerged{{Sfn|Rössler|2001|p=328}}
|-
|''U 1''
|1
|1906
|{{cvt|238|t|LT}}
|{{convert|10.8|kn}}
|{{convert|8.9|kn}}
|2 x {{convert|200|hp|abbr=on}} Korting
|2 x {{convert|200|hp|abbr=on}}
|-
|''U 2''
|1
|1908
|{{cvt|341|t|LT}}
|{{convert|13.2|kn}}
|{{convert|9.0|kn}}
|2 x {{convert|300|hp|abbr=on}} Daimler
|2 x {{convert|315|hp|abbr=on}}
|-
|[[Type U 3 submarine|Type U 3]]
|2
|1909
|{{cvt|421|t|LT}}
|{{convert|11.8|kn}}
|{{convert|9.4|kn}}
|2 x {{convert|300|hp|abbr=on}} Korting
|2 x {{convert|515|hp|abbr=on}}
|-
|[[Type U 5 submarine|Type U 5]]
|4
|1910-11
|{{cvt|505|t|LT}}
|{{convert|13.4|kn}}
|{{convert|10.2|kn}}
|4 x {{convert|225|hp|abbr=on}} Korting
|2 x {{convert|520|hp|abbr=on}}
|-
|[[Type U 9 submarine|Type U 9]]
|4
|1910-11
|{{cvt|493|t|LT}}
|{{convert|14.2|kn}}
|{{convert|8.1|kn}}
|2 x {{convert|225|hp|abbr=on}} Korting + <br/>2 x {{convert|300|hp|abbr=on}} Korting
|2 x {{convert|580|hp|abbr=on}}
|-
|[[Type U 13 submarine|Type U 13]]
|3
|1912
|{{cvt|516|t|LT}}
|{{convert|14.8|kn}}
|{{convert|10.7|kn}}
|2 x {{convert|250|hp|abbr=on}} Korting + <br/>2 x {{convert|350|hp|abbr=on}} Korting
|2 x {{convert|600|hp|abbr=on}}
|-
|''U 16''
|1
|1911
|{{cvt|489|t|LT}}
|{{convert|15.6|kn}}
|{{convert|10.7|kn}}
|2 x {{convert|242|hp|abbr=on}} Korting + <br />2 x {{convert|358|hp|abbr=on}} Korting
|2 x {{convert|600|hp|abbr=on}}
|-
|[[Type U 17 submarine|Type U 17]]
|2
|1912
|{{cvt|564|t|LT}}
|{{convert|14.9|kn}}
|{{convert|9.5|kn}}
|4 x {{convert|350|hp|abbr=on}} Korting
|2 x {{convert|560|hp|abbr=on}}
|-
|[[Type U 19 submarine|Type U 19]]
|4
|1913
|{{cvt|650|t|LT}}
|{{convert|15.4|kn}}
|{{convert|9.5|kn}}
|2 x {{convert|850|hp|abbr=on}} MAN
|2 x {{convert|600|hp|abbr=on}}
|-
|[[Type U 23 submarine|Type U 23]]
|4
|1913-14
|{{cvt|669|t|LT}}
|{{convert|16.7|kn}}
|{{convert|10.3|kn}}
|2 x {{convert|900|hp|abbr=on}} GW
|2 x {{convert|600|hp|abbr=on}}
|-
|[[Type U 27 submarine|Type U 27]]
|4
|1914
|{{cvt|675|t|LT}}
|{{convert|16.7|kn}}
|{{convert|9.8|kn}}
|2 x {{convert|1000|hp|abbr=on}} MAN
|2 x {{convert|600|hp|abbr=on}}
|-
|[[Type U 31 submarine|Type U 31]]
|11
|1914-15
|{{cvt|685|t|LT}}
|{{convert|16.7|kn}}
|{{convert|9.8|kn}}
|2 x {{convert|925|hp|abbr=on}} GW
|2 x {{convert|600|hp|abbr=on}}
|-
|[[Type U 43 submarine|Type U 43]]
|8
|1915-16
|{{cvt|725|t|LT}}
|{{convert|15.2|kn}}
|{{convert|9.7|kn}}
|2 x {{convert|1000|hp|abbr=on}} MAN
|2 x {{convert|600|hp|abbr=on}}
|}
{| class="wikitable mw-collapsible mw-collapsed"
! colspan="9" |U-boats built by Germany for foreign Navies
|-
!Type
!Nbr built
!In service
!Displacement surface
!Speed surface
!Speed submerged
!Bow tubes
!Stern Tubes
!Deck gun
|-
|''Forelle''
|1
|1904
|{{cvt|16|t|LT}}
|{{convert|5.5|kn}}
|{{convert|5.5|kn}}
|2 x 45&nbsp;cm
| --
| --
|-
|''Karp-class'' 
|3
|1907
|{{cvt|210|t|LT}}
|{{convert|10|kn}}
|{{convert|8.5|kn}}
|1 x 45&nbsp;cm
| --
| --
|-
|[[U-3-class submarine|U-3-class]] 
|2
|1909
|{{cvt|421|t|LT}}
|{{convert|12|kn}}
|{{convert|8.5|kn}}
|2 x 45&nbsp;cm
| --
| --
|-
|[[HNoMS Kobben (1909)|Kobben]]
|1
|1910-11
|{{cvt|505|t|LT}}
|{{convert|11.9|kn}}
|{{convert|8.9|kn}}
|2 x 45&nbsp;cm
|1 x 45&nbsp;cm
| --
|-
|''Atropo''{{Sfn|Navypedia Atropo|}}
|1
|1912
|{{cvt|231|t|LT}}
|{{convert|14.7|kn}}
|{{convert|8|kn}}
|2 x 45&nbsp;cm
| --
| --
|}

==World War I (1914–1918)==
=== Operations ===
{{main|U-boat campaign}}
During 1914, the U-boats operated against the British fleet: on 5 September 1914, the [[light cruiser]] {{HMS|Pathfinder|1904|6}} was sunk by {{SMU|U-21|Germany|6}}, the first ship to be sunk by a submarine using a self-propelled torpedo. On [[Action of 22 September 1914|22 September]], {{SMU|U-9||2}} sank the [[Armored cruiser|armoured cruisers]] {{HMS|Aboukir|1900|6}}, {{HMS|Cressy|1899|6}}, and {{HMS|Hogue|1900|6}}. As a result, the British [[Grand Fleet]] had to withdraw to safer waters in Northern Ireland. Against merchant ships, U-boats observed the [[Rules of Prize Warfare|"prize rules"]] which meant they had to stop and inspect the ship, and take the crew off the ship before they could sink it. On 20 October 1914, {{SMU|U-17|Germany|6}} sank the first merchant ship, {{SS|Glitra}}, off Norway. Only ten merchants were sunk in that way before policy was changed on 18 February 1915.{{Sfn|Blair||pp=9-11}}

{| class="wikitable floatright" style="text-align:left"
|+ German U-boat losses by cause
|-
|Surface warships
|{{right|55}}
|-
|Mines
|{{right|48}}
|-
|Submarines
|{{right|18}}
|-
|[[Q-ships]]
|{{right|11}}
|-
|Merchant ships
|{{right|7}}
|-
|Aircraft
|{{right|1}}
|-
|Accidents
|{{right|19}}
|-
|Unknown
|{{right|19}}
|-
|'''Total'''
|{{right|'''178'''}}
|}

On the continent German hopes for a quick victory were dashed and a stalemate had settled on the front. The Germans hoped to break the deadlock by starting an unrestricted submarine campaign against shipping in the waters around the British Isles. This was also cited as a retaliation for British minefields and shipping [[blockade]]s. Under the instructions given to U-boat captains, they could sink merchant ships, even neutral ones, without warning.{{Sfn|Blair||pp=9-11}} Only 29 U-boats were available for the campaign, and not more than seven were active around the British Isles at any time. The U-boats failed to enforce a blockade but the sinking of three liners including the [[RMS Lusitania]],{{Efn|On 7 May 1915 {{SMU|U-20|Germany|6}} sank [[Sinking of the RMS Lusitania|RMS ''Lusitania'']]; on 19 August {{SMU|U-24||6}} sank {{SS|Arabic|1902|6}}; and on 9 September ''SM U-20'' sank [[RMS Hesperian|RMS ''Hesperian'']].{{Sfn|Blair||pp=10-13}}}} with loss of American lives, outraged the US so that the [[Kaiser]] had to stop the campaign on 19 September 1915.{{Sfn|Rössler|2001|p=50}} After the stop of the campaign, most of the U-boats were sent to the Mediterranean.{{Sfn|Blair||pp=10-13}}

At the beginning of 1916, 54 U-boats were available, and the Kaiser allowed again operations around the British Isles, but with strict rules: no attacks on liners, and outside the war zone around the British Isles attacks were only allowed on armed merchant ships. But on 24 March, after 25 Americans were killed in the torpedoing of the ferry {{SS|Sussex}} the US threatened to sever [[diplomatic ties]], which persuaded the Germans to fully reapply prize rules.{{Sfn|Blair||pp=10-13}}

In September 1916, 120 U-boats were in service, and again some were sent to the Mediterranean. Whilst around British Isles prize rules were observed, in the Mediterranean a new unrestricted campaign was started. The renewed German campaign was effective, sinking {{GRT|1400000}} of shipping between October 1916 and January 1917. Despite this, the deadlock situation on the continent frontlines demanded even greater results, and on 1 February 1917, Germany restarted the unrestricted submarine campaign around British Isles. Germany took the gamble that the U-boat campaign would force the UK out of the war before the US could effectively enter. On 3 February, the US severed diplomatic relations with Germany, and on 6 April, the [[United States declaration of war on Germany (1917)|US declared war on Germany]].{{Sfn|Blair||pp=10-13}} Unrestricted submarine warfare in 1917 was very successful, sinking more than {{GRT|500000|link=off}} a month. With the introduction of convoys in August 1917, shipping losses declined to {{GRT|300000|link=off}} a month on average, which was not sufficient to force the UK out of the war. With deteriorating conditions on the continent, all U-boats were recalled on 31 October 1918.{{Sfn|Blair||pp=13-19}} Under the terms of [[armistice of 11 November 1918]], U-boats were to immediately surrender. All U-boats were either scrapped or given to Allied navies.{{Sfn|King-Hall||pp=229-242}}

Of the 373 German U-boats that had been built, 179 were operational or nearly operational at the end of the war. 178 were lost by enemy action.{{Sfn|Blair||p=18}} 512 officers and 4894 enlisted men were killed. Of the surviving German submarines, 14 U-boats were [[Scuttling|scuttled]] and 122 surrendered. They sank 10 [[pre-dreadnought battleship]]s, 18 cruisers, and several smaller naval vessels. They further destroyed 5,708 merchant and fishing vessels for a total of  {{GRT|11108865|link=off}} and the loss of about 15,000 sailors.{{Sfn|Clodfelter||p=428}} The [[Pour le Mérite]], the highest decoration for gallantry for officers, was awarded to 29 U-boat commanders.{{sfn|Möller|Brack|2004|p=185}} The three most successful U-boat commanders were [[Lothar von Arnauld de la Perière]] (195 ships with {{GRT|453,869|link=off}}), followed by [[Walter Forstmann]] (149 ships with {{GRT|391607|link=off}} ), and [[Max Valentiner]] (144 ships with {{GRT|299482|link=off}} ).{{Sfn|Wragg|2014|p=51}}

===World War I Classes===
[[File:THE IMPERIAL GERMAN NAVY'S FLANDERS FLOTILLA DURING THE FIRST WORLD WAR Q20345.jpg|thumb|upright|Sea mines are loaded in a UC coastal submarine in the harbour of Zeebrugge]]
When the German Army captured three ports on the Belgian coast in the opening stages of the war, the German navy ordered coastal submarines to be operated from these ports against the English coast. As the war was then expected to end in a matter of months, only very small {{cvt|130|t|LT}} U-boats could be designed with an expected building time of four months. On 15 October 1914 fifteen [[Type UB I submarine|Type UB I]] U-boats were ordered, and based on that design, on 23 November a further fifteen [[Type UC I submarine|Type UC I]] coastal minelaying U-boats were ordered.{{Sfn|Rössler|2001|pp=39-44}} Given the weakness of the [[Austro-Hungarian Navy]] and the need to help their [[Turkey|Turkish]] Allies, the German Navy sent some of these U-boats to the [[Dardanelles]] and [[Black Sea]].{{sfn|Möller|Brack|2004|p=202}}

In the spring of 1915 it became clear that the war would continue well into 1916 and more coastal U-boats were ordered. The Type UB I and UC I had fullfilled the expectations but were underpowered. Thirty U-boats of the successing [[Type UB II submarine|Type UB II]] were ordered, which were with around {{cvt|270|t|LT}} double in size. As with the cessation of unrestricted U-boat warfare in September 1915, mine warfare became more prominent, a record number of 64 [[Type UC II submarine|Type UC II]] minelaying U-boats were ordered, which allowed for the first time for the mass-production of a U-boat. The Type UC II proved to be an ideal combination of mine and torpedo armament: on the same patrol it could lay minefields and attack shipping on the way to its target.{{Sfn|Rössler|2001|pp=50-53}}

On the resumption of the U-boat campaign in 1916, it was realized that not enough large U-boats could be built in time, and as a compromise it was decided to build an enlargened coastal U-boat capable of patrolling in the [[Western Approaches]]. The hull of the Type UC II was taken as a basis, the forward mineshaft room was replaced with a torpedo room, more powerfull diesel engines provided better surface speed and larger fuel tanks extended the range. On 2 May 1916 the first twenty-four [[Type UB III submarine|Type UB III]] were ordered and as the war prolonged, more than 200 were ordered but only 96 were commissioned before the armistice.{{Sfn|Rössler|2001|pp=56-57}}{{sfn|Möller|Brack|2004|pp=46-54}} 
{| class="wikitable"
|-
|standard U-boat types
|[[German Type U 51 submarine|Type U 51]], [[German Type U 57 submarine|Type U 57]], [[German Type U 63 submarine|Type U 63]], [[German Type U 66 submarine|Type U 66]], [[Type U 81 submarine|Type U 81]], [[Type U 87 submarine|Type U 87]], [[Type U 93 submarine|Type U 93]] 
|-
|U-cruisers and merchant U-boat types
|[[German Type U 139 submarine|Type U 139]], [[German Type U 142 submarine|Type U 142]], [[German Type U 151 submarine|Type U 151]], [[German Type UD 1 submarine|Type UD 1]]
|-
|UB coastal U-boat types
|[[German Type UB I submarine|Type UB I]], [[German Type UB II submarine|Type UB II]], [[German Type UB III submarine|Type UB III]], [[German Type UF submarine|Type UF]], [[German Type UGsubmarine|Type UG]]
|-
|UC coastal minelaying U-boat types
|[[German Type UC I submarine|Type UC I]], [[German Type UC II submarine|Type UC II]], [[German Type UC III submarine|Type UC III]]
|-
|UE ocean minelaying U-bot types
|[[German Type UE I submarine|Type UE I]], [[German Type UE II submarine|Type UE II]]
|}

==Interwar years (1919–1939)==
[[File:Vetehinen-Crichton-Vulcan-1930.jpg|thumb|The Finnish submarine ''Vetehinen'' in 1930 on the slipways at the [[Crichton-Vulcan]] shipyard in [[Turku]], Finland]]

=== Construction ===
The [[Treaty of Versailles]] ending World War I signed at the [[Paris Peace Conference, 1919|Paris Peace Conference]] in 1919 limited the surface navy of Germany's new [[Weimar Republic]] to only six [[battleship]]s, six [[cruiser]]s, twelve [[destroyer]]s and twelve [[torpedo boat]]s. The treaty also restricted the independent tonnage of ships and forbade the construction of submarines.{{Sfn|Humble||p=25}} In order to circumvent the restrictions of the treaty, a submarine design office called [[NV Ingenieurskantoor voor Scheepsbouw|Ingenieurskantoor voor Scheepsbouw]] (IVS) was set up in the [[Netherlands]]{{Sfn|Costello & Hughes||p=26}} The IVS was run by Krupp and made it possible to maintain a lead in submarine technology by designing and constructing submarines in Holland for other nations.{{Sfn|Blair||p=24}} The IVS made designs for small 250-ton U-boats, medium 500-ton U-boats and large 750-ton U-boats.{{Sfn|Blair||p=31}}

The IVS constructed three 500-ton medium submarines in Finland between 1927 and 1931, known as the [[Vetehinen-class submarine|Vetehinen-class]]. These ships were the prototypes for the subsequent German [[Type VII submarine|Type VII]] U-boat. In 1933 a small 250-ton submarine, the [[Finnish submarine Vesikko|''Vesikko'']] was built. This submarine was nearly identical to the subsequent German [[Type II submarine|Type II]] U-boat. A fifth very small 100-ton submarine, the [[Finnish submarine Saukko|Saukko]] was built in 1933 as well. In Spain a large 750-ton boat was built between 1929 and 1930. After the Spanish lost interest in the U-boat, they sold it to Turkey where it entered service as [[TCG Gür (1936)|Gür]]. German sailors assisted in the trials for these submarines. These secret programs were exposed in the [[Lohmann Affair]] and as a result the Head of the {{lang|de| [[Reichsmarine]]}}, [[Hans Zenker]], had to resign. His successor [[Erich Raeder]] continued the policy of secretly breaching the Versailles treaty. On 15 November 1932, a plan was approved for an expansion of the German navy which included U-boats.{{Sfn|Blair||pp=31-32}}

[[File:U-boot E-1.png|thumb|The Spanish submarine E-1 in Cadiz]][[File:u534.jpg|thumb|[[German submarine U-534|''U-534'']], a type IX U-boat at Birkenhead Docks, Merseyside, England]]In 1935, Britain sought to limit Germany's increasingly apparent breaches of the Versailles treaty, negotiating the [[Anglo-German Naval Agreement]]. Under the agreement, Germany was relieved of some Treaty of Versailles restrictions and permitted to build ships in a 100:35 tonnage ratio to the British fleet. For submarines the Germans obtained parity in tonnage, but promised a 45 percent limit unless special circumstances arose.{{Sfn|Costello & Hughes||p=28}} This allowed 24,000 tons for U-boat building. Only one week after the agreement was signed, the first of six Type II U-boats, {{GS|U-1||2}} was commissioned in the German Navy, which changed name from {{lang|de|Reichsmarine}} (Imperial Navy) to {{lang|de|[[Kriegsmarine]]}} (War Navy).{{Sfn|Blair||pp=34-35}} Within the year, the Germans commissioned a total of 36 U-boats for a total of 12,500 tons:{{Sfn|Blair||p=40}}
* Twenty-four small 250-ton Type II U-boats
* Ten medium 500-ton Type VII U-boats
* Two large 750-ton [[German Type I submarine|Type I]] U-boats, based on the design of the Spanish submarine

[[Karl Dönitz]] was appointed as head of the submarine section of the {{lang|de|Kriegsmarine}}. He believed firmly that in spite of the Anglo-German Naval agreement and Hitler's policy of avoiding conflict with Britain, the next war would be with Britain. He requested the remaining 11,500&nbsp;tons be used to build twenty-three medium submarines, which he considered ideal for a commerce war against British convoys. Raeder disagreed, and opted for a more balanced expansion of the submarine fleet:{{Sfn|Blair||p=40}}
* Eight small 250-ton improved type II U-boats
* Seven medium 500-ton U-boats. The type VII was designed with a single rudder and this had two drawbacks: as the rudder was not in the wash of the two propellers, the rudder response was not good. The stern torpedo tube had also to be mounted externally as the rudder obstructed the exit of an internal tube. As a consequence, this tube could not be reloaded. Hence the type VII was upgraded to type VIIB with dual rudders to improve maneuverability and to fit an internal stern tube with a reload.{{Sfn|Paterson|2003|p=x-xi}}
* Eight large 750-ton U-boats. The Type I was found to be unsatisfactory, suffering the same single rudder maneuverability problems of the Type VII and a very poor diving time. The gravity center of the U-boat was too forward, so when surfaced the Type I had its propellers exposed when pitching. Whilst submerged, it suffered problems with depth keeping and stability caused by the wobbling of air bubbles in the fuel tanks.{{Sfn|Paterson|2003|p=x-xi}} Hence a new [[German Type IX submarine|Type IX]] design for a large U-boat was made.

Twenty-one of these twenty-three U-boats were commissioned before World War II. In 1937, Britain announced it would expand its submarine fleet from 52,700 to 70,000&nbsp;tons. Again, Raeder decided that the extra 7,785&nbsp;tons would be divided between medium and large U-boats:{{Sfn|Blair||p=45}}
* Seven medium 500-ton Type VIIB U-boats
* Five large 750-ton of the improved Type IXB U-boats
[[File:80-G-700007 Battle of the Atlantic. German Submarine U-233 sinking after being rammed by USS Thomas (DE 102).jpg|thumb|A Type XB submarine sinking in the Atlantic. On the foredeck the vertical mineshafts are visible.]]
During 1938, Hitler changed his attitude towards Britain. Whilst he still hoped that Britain would not interfere in his foreign policy, he needed a navy that could act as a deterrent. Hitler wanted to invoke the escape clause of the naval agreement and to have 70,000&nbsp;tons of submarines. Between May 1938 and January 1939, Raeder ordered 52 more U-boats to be completed by 1942:{{Sfn|Blair||pp=46-47}}

* Twenty-one medium 500-ton Type VIIB U-boats
* Eleven large 750-ton Type IXB U-boats
* Three very large Type XB minelaying U-boats
* Four huge Type XI U-cruisers
In 1939, the ambitious [[Plan Z]] was launched. It called for the construction of a German navy capable of challenging the Royal Navy. The plan included 249 U-boats for a total of 200,000 tons. But when World War II broke out only months after the plan was announced, only a handful of the planned U-boats ended up being built.{{Sfn|Blair||pp=46-47}}

When World War II started, Germany had 56 U-boats commissioned, of which 46 were operational and 22 having sufficient range for Atlantic operations; the other 24 were limited to [[North Sea]] operations.{{Sfn|Mason||pp=|p=23}}

=== Developments ===
[[File:Bundesarchiv Bild 101II-MW-5536-01, Wilhelmshaven, U-Boot, Torpedo-Übernahme.jpg|thumb|A torpedo is loaded into a U-Boat through a torpedo hatch.]]
German U-boat designs of World War II were significant improvements over their World War I equivalents. By using new steel alloy and [[welding]] instead of [[rivet]]ing, they had stronger hulls and could dive deeper. The diving time was improved to thirty seconds for a medium U-boat. The power of diesel engines rose, allowing higher speeds while surfaced. Range was  increased by installing [[Saddle tank (submarine)|saddle tanks]], which were on open to the sea on the bottom in order to balance pressure, with the diesel fuel floating freely atop the seawater. A technique was developed for economical cruising where only one of the two diesel engines would be run and would drive the two propeller shafts through a coupling with the two electro engines.{{Sfn|Blair||pp=|p=37}}

Another vast improvement was the introduction of new torpedo types for the U-boats: the classic [[G7a torpedo]] propelled by compressed air had a much larger warhead than its WWI equivalent, but more important was the introduction of the electric [[G7e torpedo]].{{Sfn|Bekker||p=129}} Though slow with range limitations, it left no telltale bubble wake, making it ideal for daylight attacks.{{Sfn|Blair||pp=|p=37}} During WWI, the Germans had briefly experimented with [[magnetic pistol]]s and these were further developed now as the standard pistol for torpedoes. The classic contact pistol required a torpedo to detonate against the ship's hull, whilst a magnetic torpedo could detonate below a ship, resulting in a much more damaging explosion. Thus, it was hoped that one torpedo would suffice to break the back of a ship, and a U-boat could sink many more ships with its supply of torpedoes.{{Sfn|Blair||p=38}}{{Sfn|Bekker||p=120}}

All U-boats were now also equipped with long- and short-wave transmitters, enabling communications with bases ashore and with other U-boats. This allowed for better operational information and guidance.{{Sfn|Blair||p=38}}

=== U-Boat design and layout ===
[[File:VIIC uboat shaded.svg|thumb|upright=1.8|Cross-section of a Type VII U-boat]]
From bow to stern, A typical U-boat design comprised these sections:

* Bow torpedo room. The torpedo tubes were loaded but torpedoes needed maintenance so there was space to unload the tubes. Below the floor plates four spare torpedoes were stored. Two more spares were stored above the floorplates where they occupied much of the available space. The crew responsible for the torpedo maintenance and launching had their sleeping bunks in this compartment, along with the lowest ratings on board. As long as the two spare torpedoes above the floorplates were not launched, living conditions were very cramped here. Once launched, space for extra bunks became available but, anyway, there were not enough sleeping bunks for all the crew, and these were 'hot bunks' which switched occupants as they went on or off duty.{{Sfn|Blair||p=|pp=57-59}}{{Sfn|Paterson||pp=55-56}}
* Crew quarters for [[officer]]s and [[chief petty officer]]s,{{Sfn|Gannon||p=34}} with a battery compartment below decks.{{Sfn|Blair||p=|pp=57-59}} The captain had a curtained bunk which faced two small rooms: the radio room and the hydrophone room.{{Sfn|Gannon||p=34}}
* Control room. The main large [[periscope]], for general use, was located here. The rudder, [[diving planes]], [[Ballast tank|ballast]] and trim tanks were operated here with valves and buttons. Below decks, there was space to retract the periscope and to store ammunition for the deck gun. A cylindrical tube with a ladder led to the [[conning tower]].{{Sfn|Blair||p=|pp=57-59}}
* Conning tower. This space protruded from the cylindrical hull but was still within the pressure hull. Here, the angle and depth settings for the torpedoes were calculated with an analogue data solver. During submerged attacks the captain was on station here, operating the second, smaller attack periscope, which generated less wake at the surface. Above the conning tower was the bridge.{{Sfn|Blair||p=|pp=57-59}} 
* Aft crew quarters for [[petty officer]]s, with another battery compartment below decks. The galley and toilet were also located here.{{Sfn|Blair||p=|pp=57-59}}
* Engine (diesel) room. The diesel engines needed air, which was supplied through a pipe outside the pressure hull from the bridge, as high as possible from sea level. There was no exhaust pipe; in order to reduce smoke the exhaust was mixed with sea water. The diesel engine could drive an air compressor in order to feed air tanks needed for venting the ballast tanks.{{Sfn|Blair||p=62}}[[File:VII C U-Boot E-Maschine b.jpg|thumb|upright|The electrical room]]
* Electrical or motor room. The electric motors were driven by the batteries. Alternatively, when driven by the diesel engines, the motors acted as generators for recharging the batteries.{{Sfn|Blair||p=62}}
* Aft torpedo room. Only bigger type IX U-boats had such a compartment. Smaller U-boats did not have aft torpedo tubes at all, or had a single torpedo tube installed in the motor room, with a spare torpedo stored below decks between the engines.{{Sfn|Blair||p=62}}

==World War II (1939–1945)==

=== Operations ===
{{Main|Battle of the Atlantic}}

During World War II, U-boat warfare was the major component of the Battle of the Atlantic, which began in 1939 and ended with Germany's surrender in 1945. British prime minister [[Winston Churchill]] later wrote "The only thing that really frightened me during the war was the U-boat peril."{{Sfn|Churchill||p=529}}

[[File:Base ssmarin stnazaire.jpg|thumb|left|[[Submarine pen|U-boat pens]] in [[Saint-Nazaire]], France]]
As convoying had been key in the defeat of German submarines during World War I, the British began organizing convoys at once in September 1939. The most common U-boat attack against convoys during the early years of the war was conducted on the surface and at night. During 1939 the Germans made a few attempts to attack convoys with their new 'wolfpack' tactic, but these were not successful. The [[Operation Weserübung|invasion of Norway]] in April 1940 temporarily halted all U-boat operations against merchant shipping. During the invasion many technical problems with the German torpedoes were exposed and only in August 1940 could the campaign against convoys be revived. There were now fewer U-boats operational than at the beginning of the war, but thanks to the new bases in France and Norway U-boats could reach their operation grounds far more easily. During the following months the U-boats put their 'wolfpack' tactic against convoy in practice with spectacular results. This period, before the Allied forces developed truly effective antisubmarine warfare tactics, was referred to by German submariners as [[First Happy Time|the happy time]] ({{lang|de|die glückliche Zeit}}).<ref name="milHisOnline">{{Cite web |title=Military History Online |url=https://www.militaryhistoryonline.com/wwii/atlantic/uboatwar.aspx |access-date=2019-02-04 |website=www.militaryhistoryonline.com |archive-date=6 November 2018 |archive-url=https://web.archive.org/web/20181106234233/https://www.militaryhistoryonline.com/wwii/atlantic/uboatwar.aspx |url-status=dead }}</ref>

In the beginning of 1941, British countermeasures began to take effect: in March 1941, the three leading U-boat aces were sunk during convoy battles. In May 1941, the British were able to [[Ultra (cryptography)|break]] into German secret naval [[Enigma machine|Enigma]] communications and could henceforth reroute convoys around U-boat concentrations.{{Sfn|Costello & Hughes||pp=154–155}} When American warships started to escort Atlantic convoys, the U-boats were restricted in their operations as Hitler wanted to avoid conflict with the US.{{Sfn|Costello & Hughes||p=165}} The campaign against merchant shipping received further impediments when Hitler interfered on two occasions: first he insisted that a small force of U-boats be kept on station in the [[Arctic]] as a precaution against a possible Allied invasion in Norway,{{Sfn|Blair||pp=357–358}}{{Sfn|Mason||p=68}} and next, he ordered a substantial force of U-boats to operate in the Mediterranean in order to support the Italians and [[Erwin Rommel|Rommel's]] [[Afrika Korps]].{{Sfn|Mason||p=54}}[[File:Captured German U-boats outside their pen at Trondheim in Norway, 19 May 1945. BU6382.jpg|thumb|upright=.9|Captured [[German Type VII submarine|Type VII]] and [[German Type IX submarine|Type IX]] U-boats outside their pen in [[Trondheim]], Norway, 19 May 1945]]When the US entered the war, the focus of U-boat operations shifted to the Atlantic coast of the United States and Canada, where no convoys were organized and anti-submarine measures were inadequate. There followed a [[Second Happy Time]] when U-boats could extend their successful operation to the [[Gulf of Mexico]] and the [[Caribbean Sea]].{{Sfn|Mason||pp=72–73}} By mid-1942 an adequate defense was organized in these regions; U-boats returned to their original and crucial hunting grounds on the North Atlantic convoy lanes.{{Sfn|Blair||p=654}} The renewed offensive against convoys reached its climax in March 1943, when two-thirds of all ships sunk had been sailing in convoys.{{Sfn|Mason||p=108}} The Allies put effective countermeasures into effect, and only two months later on 24 May, Dönitz had to stop the campaign due to heavy losses.{{Sfn|Rohwer||p=252}}

By the end of the war, almost 3,000 Allied ships (175 warships; 2,825 merchant ships) had been sunk by U-boats.<ref name="Tread">{{cite book |last=Crocker III |first=H. W. |url=https://archive.org/details/donttreadonme40000croc/page/310 |title=Don't Tread on Me |publisher=Crown Forum |year=2006 |isbn=978-1-4000-5363-6 |location=New York |page=[https://archive.org/details/donttreadonme40000croc/page/310 310] |url-access=registration}}</ref> In total, 1181 U-boats entered service before the German surrender, of which 863 executed war patrols, and 785 were lost.{{Sfn|Haskell||p=14}}{{Sfn|Middlebrook||p=327}} 222 U-boats were scuttled by their crews and 174 surrendered to Allied forces.{{Sfn|Blair Vol2||p=700}} 121 U-boats were scuttled in 1945-46 during [[Operation Deadlight]].{{Sfn|Rohwer||pp=432-433}}

===U-boat developments===
[[File:Type XXI section.jpg|thumb|A prefabricated segment of a Type XXI U-boat. The cross-section shows clearly the '8'-shaped hull, where the lower part was used to store large batteries hence the name of 'ElektroBoot']]
In 1940 the Germans made successful tests with the [[German submarine V-80|V-80]] experimental submarine featuring a new type of propulsion: surfaced, it used the classic diesel engines, but submerged it used a revolutionary [[hydrogen peroxide]] [[air-independent propulsion|air-independent]] [[hydrogen peroxide#Propellant|propellant]] system designed by [[Hellmuth Walter]]. With this Walter-turbine, underwater speeds of above 20 knots were possible, much greater than the 4-knot cruising and 6-knot maximum speeds attainable through battery-powered electrical engines. Four more experimental [[German Type XVIIB submarine|Type XVIIA]] U-boats with Walter turbines were built and tested but could not be implemented into a big frontline U-boat.{{Sfn|Blair Vol2||pp=10-11}}{{Sfn|Costello & Hughes||pp=284–285}} Unlike a classic U-boat that could recharge its batteries with the diesel engines, once a Walter U-boat had consumed its hydrogen peroxide propellant it could not submerge anymore. The Germans did not possess the resources and plants to produce sufficient hydrogen peroxide to operate a fleet of Walter submarines. Despite these limitations, 24 frontline Type XVIIB coastal submarines were ordered, but only three were built and none were operational before the end of the war.{{Sfn|Blair Vol2||p=312}}

The Walter U-boats had very large hulls to store fuel for submerged propulsion. Once it became clear these Walter U-boats would not be operational in time, the Walter U-boat hull design was reused with a different approach: the space for the hydrogen peroxide tanks was used to store much larger batteries. With massively increased battery power, U-boats enjoyed much greater speeds and endurance when submerged.{{Sfn|Breyer||pp=7–13}} Based on the design of an Atlantic Walter U-boat, the [[German Type XXI submarine|Type XXI]] "{{lang|de|Elektroboot}}" was designed to boost submerged performance. Smaller [[German Type XXIII submarine|Type XXIII]] coastal {{lang|de|Elektroboote}} were also taken into production. These {{lang|de|Elektroboote}} were mass-produced, with prefabricated segments constructed at different sites and then assembled at the bigger shipyards.{{Sfn|Blair Vol2||pp=312–313}}{{Sfn|Costello & Hughes||pp=285-287}}
[[File:Submarine snorkel.png|thumb|The {{lang|de|Schnorkel}} mast and air flows]]
After the [[German invasion of the Netherlands]] in 1940, the Germans captured some Dutch submarines equipped with a [[Submarine snorkel|''Schnorchel'']] (snorkel) but saw no need for them until 1943. The {{lang|de|Schnorchel}} was a retractable pipe that supplied air to the diesel engines while submerged at [[periscope depth]], allowing the boats to cruise submerged on diesel engines and recharge their batteries.{{Sfn|Breyer||p=8}} It was far from a perfect solution: problems occurred with the device's valve sticking shut or closing as it dunked in rough weather; since the system used the entire pressure hull as a buffer, the diesels would instantaneously suck huge volumes of air from the boat's compartments, often causing painful ear injuries. Speed was limited to {{convert|8|kn|km/h}}, lest the device snap from stress. Whilst running submerged with the {{lang|de|Schnorchel}}, the [[Gruppenhorchgerät]] was rendered useless by diesel engine noise. The {{lang|de|Schnorchel}} nonetheless allowed old Type VII and IX U-boats to operate in waters that previously denied to them.{{Sfn|Costello & Hughes||p=284}}

===Classes===
* [[German Type I submarine|Type I]]: first design for a large 750-ton U-boat. Only 2 built as the design was not very successful.
* [[Type II submarine|Type II]]: small coastal submarines used mainly for training purposes. The latest subtype IID had saddle tanks which gave it a range to operate in the Atlantic, which it did until 1941
* [[German Type VII submarine|Type VII]]: the "workhorse" of the U-boats with 709 completed in World War II
* [[German Type IX submarine|Type IX]]: these long-range U-boats operated as far as the Indian Ocean with the Japanese ([[Monsun Gruppe]]), and the [[South Atlantic]]
* [[German Type X submarine|Type X]]: long-range minelayers but mainly used to resupply other U-boats
* [[German Type XIV submarine|Type XIV]]: lightly armed with no torpedo tubes and light AA, used to resupply other U-boats; nicknamed the {{lang|de|Milchkuh}} ("Milk Cow")
* Type XVII: small experimental coastal submarines powered by experimental hydrogen peroxide propulsion systems, not put into service
* [[German Type XXI submarine|Type XXI]]: known as the {{lang|de|Elektroboot}}. The design was taken into mass production, but only two set out for a war patrol before the end of the war
* [[German Type XXIII submarine|Type XXIII]]: smaller version of the XXI used for coastal operations. operated on a small scale during 1945
* [[Midget submarine]]s, including [[Biber (submarine)|''Biber'']], [[Hai (midget submarine)|''Hai'']], ''[[Molch]]'', and ''[[Seehund]]''
* [[Uncompleted U-boat projects]]

==Post–World War II and Cold War (after 1945)==
[[File:Bundesarchiv Bild 146-2008-0212, Uboot Hecht (S 171, ex U 2367).jpg|thumb|Type XXIII U-Boat ''Hecht'' in 1957.]]

=== Type 201, 202 and 205 ===
The [[London and Paris Conferences]] in 1954 paved the way for [[West Germany]] to join [[NATO]], and from 1955 the West German {{lang|de|[[Bundesmarine]]}} was allowed to commission submarines up to 350 tons for coastal operations. Two classes were designed: the 350-ton [[Type 201 submarine|Type 201]] and the 100-ton [[Type 202 submarine|Type 202]]. Pending the completion of the first of these U-boats, the Bundesmarine needed submarines to test the new equipment and to train crews. No submarines could be purchased from foreign navies, so in 1957, two Type XXIIIs and a Type XXI U-boats sunk in 1945 were raised and repaired. In 1959, twelve Type 201 and three Type 202 U-boats were ordered. As both types were designed to be deployed in the [[Baltic Sea]], they were built in [[ferromagnetism|non-magnetic]] steel to protect against magnetic [[naval mine]]s and [[magnetic anomaly detector]]s. By using non-ejectable, non-reloadable torpedo tubes which needed much less space because of smaller fittings and the absence of compensation trim tanks, it was possible to mount eight tubes in the small Type 201. The Type 202 was even smaller and equipped with two torpedo tubes.{{Sfn|Rössler|2001|pp=302-304}}

The first three Type 201 U-boats were commissioned in 1962. To continue the U-boat tradition, the new boats received the classic "U" designation starting with ''U-1''. In 1962, a redefinition of the tonnage calculation to include solid ballast meant the Type 201 would  displace 395 tons. Consequently, tonnage limits established in the London and Paris Conferences were increased to 450 tons for current submarines and future U-boats limited to 1,000 tons. During construction of the first U-boats, it became apparent that an extra sonar needed to be installed. Since the Type 201 was constructed in sections, it was easy to enlarge the hull with an extra 1.8-meter section to accommodate the sonar. This extra section increased displacement to 420 tons, remaining well-within conference limits. Deemed the [[Type 205 submarine|Type 205]], five of these enlarged vessels would be completed by the end of 1963.{{Sfn|Rössler|2001|p=|pp=308-309}}

=== Type 206 and 207 ===
In 1962, Norway placed an order for fifteen coastal submarines. In order to train crews, ''U-3'' was loaned to the [[Royal Norwegian Navy|Norwegian Navy]], between 10 July 1962 and 20 June 1964, she was named HNoMS ''Kobben''.{{Sfn|Rössler|2001|p=308}} The fifteen U-boats built between 1963 and 1967 had a high-tension steel hull for increased diving depth and were classified as [[Kobben-class submarine|Type 207]].{{Sfn|Rössler|2001|pp=317-318}} The [[Royal Danish Navy|Danish Navy]] bought the licences to build two coastal submarines based on the Type 205 plans in 1965.  Due to complications with the installation of Danish equipment in these designs, construction was not completed until 1970.{{Sfn|Rössler|2001|p=318}}[[File:Submarines S194 and S196.jpg|thumb|''The Type 206 U-15'' and ''U-17.'']]By 1963, it became obvious that the new non-magnetic steel had corrosion problems when small cracks began to form in the pressure hull. Whilst U-3 continued training and testing in the Norwegian Navy, ''U-1'' and ''U-2'' were laid up. The five U-boats ''U-4'' to ''U-8'' received zinc paint coating to protect the hull, but nevertheless had to undergo regular testing of their maximum diving depth.{{Sfn|Rössler|2001|p=309}} Eventually, these five U-boats were assigned to the U-boat Training Group. Two new hulls in classic magnetic steel were built, and as much as possible equipment of the old Type 201 ''U-1'' and ''U-2'' was recovered for these new type 205 U-boats, which received the same identification ''U-1'' and ''U-2''. Meanwhile, the German Navy found little use for the two ordered Type 202 U-boats had been completed by 1965; these U-boats did not receive an official U-boat number but were named ''Hans Techel'' and ''Friedrich Schürer.'' They were only in service with the Test Centre of U-boats until end of 1966. The last four U-boats ''U-9'' to ''U-12,'' from the original order of twelve U-boats were constructed with new non-magnetic steel which delayed their delivery to the Navy until 1967-1969.{{Sfn|Rössler|2001|pp=311-312}}

=== Type 209 and variants ===
In 1968, the German Navy ordered twelve more coastal submarines, named ''U-13'' to ''U-24.'' The Type 205 design was again enlarged, accommodating extra batteries to feed the ever-increasing array of electronics. This resulted in the 450-ton [[Type 206 submarine|Type 206]]. A further six of these U-boats named ''U-25'' to ''U-30'' were ordered in 1970 to replace the six faulty U-boats ''U-3'' to ''U-8''. The German Navy wanted to order six larger Type 208 submarine-hunter U-boats, and although permission was obtained from the [[Western European Union]] for construction up to 1,000 tons, this order was never placed because there were financial burdens with the fiasco of the nonmagnetic U-boats and since a diesel-electric submarine was too slow as a submarine hunter for nuclear propelled submarines.{{Sfn|Rössler|2001|pp=312-317}}

Having secured the permission to build larger submarines, the [[Type 209 submarine|Type 209]] diesel-electric submarine was designed as a much larger Type 205, with the same characteristics and armament, but with much larger battery capacity, the possibility for torpedo reloads and extra sensors. It was proposed as a very customizable export-sales submarine, available in five variants with a displacement between 1,000–1,500&nbsp;tons. The first customer was the [[Hellenic Navy]], which received four Type 209's in 1971-72. {{As of |2002}}, fifty-one boats had been built for thirteen navies, with another twelve still ordered.{{Sfn|Miller|2002|pp=256-261}}{{Sfn|Rössler|2001|pp=317-322}} In 1974, three 540 tons U-boats were built for the [[Israeli Navy]]. Based both on the type 206 and as a smaller Type 209, these three U-boats were classified as the [[Gal-class submarine|Type 540]]. For political reasons these U-boats were not built in Germany but by [[Vickers Limited]] in England.{{Sfn|Miller|2002|pp=254-255}}{{Sfn|Rössler|2001|p=322}} In 1982, the Norwegian Navy ordered six 1,000 tons U-boats, to replace half of the Kobben-class submarines, these were classified as the [[Ula-class submarine|Type 210]].{{Sfn|Miller|2002|p=262}} After receiving two Type 209 U-boats in 1974,{{Sfn|Rössler|2001|p=317}} the [[Argentine Navy]] ordered six larger 2,000 tons [[TR-1700-class submarine|TR-1700]] U-boats in 1977. Two of these were built in Germany and delivered after the [[Falklands War]] in 1984-85, the remaining four were to be built in Argentina, but these were never completed.{{Sfn|Miller|2002|pp=264-265}} In the early 1990s, Israel ordered three 1,565 tons submarines which were enlarged versions of the Type 209 but resembled more the later Type 212. The first three submarines were delivered in 1999-2000 as the [[Dolphin-class submarine|Dolphin-class]] or Type 800.{{Sfn|Miller|2002|pp=262-263}}

[[File:U Boot 212 HDW 1.jpg|thumb|right|[[Type 212 submarine]] with air-independent propulsion of the [[German Navy]] in dock at [[Howaldtswerke|HDW]]/[[Kiel]]]]

=== Type 212 and variants ===
In 1998, Germany started to construct the first of six [[Type 212 submarine|Type 212]] U-boats. Before the first was launched, two were ordered by Italy, and Greece ordered four enlarged Type 212 U-boats, which were classified as [[Type 214 submarine|Type 214]].{{Sfn|Miller|2002|pp=326-328}} Between 2005 and 2007, the four Type 212 {{GS|U-31|S181|2}}, {{GS|U-32|S182|2}}, {{GS|U-33|S183|2}} and {{GS|U-34|S184|2}} were commissioned in the German Navy{{Sfn|Bundeswehr|}} and two in the Italian Navy.{{Sfn|NavTech Todaro|}} In 2015–2016, a further two Type 212 {{GS|U-35|S185|2}} and {{GS|U-36|S186|2}} were delivered to the German Navy,{{Sfn|Bundeswehr|}} and in 2016-2017, the Italian Navy commissioned also two more Type 212.{{Sfn|NavTech Todaro|}} The Type 212 features an air-independent propulsion system using [[hydrogen]] [[fuel cell]]s.{{Sfn|Miller|2002|pp=326-328}}{{Sfn|Bundeswehr|}} While the Type 212 is also being purchased by Norway,{{Sfn|Berg Bentzrød||}} the Type 214 has been designed as the follow-on export model. Nine Type 214s have been sold to South Korea and were delivered between 2007 and 2020. Two were delivered to Portugal as [[Tridente-class submarine|Type U 209PN]] sub-class U-boats in 2010-2011.{{Sfn|GlobalSecurity Type214/209PN|}} Six Type 214s were ordered by Turkey in 2011 as the [[Reis-class submarine|Reis-class]] for construction at the [[Gölcük Naval Shipyard]].{{Sfn|GlobalSecurity Reiss|}} The first was commissioned in 2024.{{Sfn|NavalNews|}}

The [[Type 216 submarine|Type 216]] was a design for a 4,000 tons U-boat with a much larger endurance. It was proposed to but was not bought by Australia. {{As of |2025}}, no Type 216s have been ordered.{{Sfn|GlobalSecurity Type216|}} Between 2022 and 2024, Germany built four 2,000 tons [[Invincible-class submarine|Type 218]] U-boats for the [[Republic of Singapore Navy]], which are based on the Type 212 and Type 214, with the same propulsion method and 'X' rudder, but armed with eight torpedo tubes.{{Sfn|NavTech Invincible|}}

==See also==
* [[List of U-boats never deployed]]
* [[List of successful U-boats]]
* [[List of U-boats of Germany]]
*[[Austro-Hungarian U-boat classes]]
* [[I-boat]], Japanese equivalent
* [[List of Knight's Cross recipients of the U-boat service]]
* [[Möltenort U-Boat Memorial]]
* ''[[Das Boot]]'', 1981 German U-boat film
* 
* ''[[Aces of the Deep]]'', 1994 U-boat simulator 
** ''[[Silent Hunter II]]'', second of a series
** ''[[Silent Hunter III]]'', third of a series
* [[Uboat (video game)|''Uboat'']], 2024 U-boat simulator

==Footnotes==

=== Notes ===
{{notelist}}

=== Citations ===
{{reflist|20em}}

==References==

* {{Cite book |last=Bekker |first=Cajus |title=Verdammte See |publisher=Gerhard Stalling Verlag |year=1971 |isbn=3-548-03057-2 |location=Oldenburg |language=de |ref={{sfnref|Bekker}}}}
* {{cite news |last=Berg Bentzrød |first=Sveinung |date=3 February 2017 |title=Forsvaret kjøper nye ubåter fra Tyskland |trans-title=The Armed Forces are purchasing new submarines from Germany |url=http://www.aftenposten.no/norge/Forsvaret-kjoper-nye-ubater-fra-Tyskland-614432b.html |language=no |newspaper=[[Aftenposten]] |location=[[Oslo]] |publisher=Aftenposten AS |access-date=9 March 2019 |ref={{sfnref|Berg Bentzrød}}}}
* {{Cite book |last=Blair |first=Clay |title=Hitler's U-Boat War: The Hunters 1939–1942 |publisher=Cassell |year=1998 |isbn=0-304-35260-8 |volume=1 |ref={{sfnref|Blair}}}}
* {{Cite book |last=Blair |first=Clay |title=Hitler's U-Boat War: The Hunted 1942–1945 |publisher=Cassell |year=1998 |isbn=0-304-35261-6 |volume=2 |ref={{sfnref|Blair Vol2}}}}
*{{Cite book |last=Breyer |first=Siegfried |title=Wunderwaffe Elektro-Uboot Typ XXI |publisher=Podzun-Pallas-Verlag |year=1996 |isbn=3-7909-0587-9 |language=de |ref={{sfnref|Breyer}}}}
* {{cite book |last1=Chaffin |first1=Tom |url=https://books.google.com/books?id=pQcjlDMjXFoC |title=The H. L. Hunley: The Secret Hope of the Confederacy |date=2010 |publisher=Macmillan |isbn=978-1429990356 |page= |quote= |ref={{sfnref|Chaffin}} |access-date=2016-07-14}}
* {{Cite book |last=Churchill |first=Winston |title=The Second World War, Volume 2: Their Finest Hour. |publisher=Houghton Mifflin |year=1948 |ref={{sfnref|Churchill}}}}
* {{cite book |author=Clodfelter |first=Micheal |title=Warfare and Armed Conflicts: A Statistical Encyclopedia of Casualty and Other Figures, 1492–2015 |date=2017 |publisher=McFarland |edition=4th |ref={{sfnref|Clodfelter }}}}
* {{Cite book |last1=Costello |first1=John |title=The Battle of the Atlantic |last2=Hughes |first2=Terry |publisher=Collins |year=1977 |isbn=0-00-635325-8 |location=London |ref={{sfnref|Costello & Hughes}}}}
* {{Cite book |last=Fischer |first=Bruno |title=Ehrenbuch des Orden vom Militär-Verdienst-Kreuz e.V. und die Geschichte der Ordens-Gemeinschaft, Die Ordens-Sammlung |year=1960 |language=de |ref={{sfnref|Fischer}}}}
* {{Cite book |last=Gannon |first=Michael |title=Black May. The epic story of the Allies' defeat of the German U-boats in May 1943 |publisher=Aurum Press |year=1998 |isbn=1-85410-588-4 |ref={{sfnref|Gannon}}}}
* {{Cite book |last=Haskell |first=Winthrop A. |title=Shadows on the Horizon. The battle of Convoy HX-233 |publisher=Chatham Publishin |year=1998 |isbn=1-86176-081-7 |location=London |ref={{sfnref|Haskell}}}}
* {{Cite book |last=Humble |first=Richard |title=De Duitse Kriegsmarine |publisher=Standaard Uitgeverij |year=1974 |isbn=90-02-12787-1 |edition=2nd |location=Antwerp |language=nl |ref={{sfnref|Humble}}}}
* {{Cite web |last=King-Hall |first=Stephen |date=19 May 2021 |title=A North Sea diary, 1914–1918 / Commander Stephen King-Hall |url=http://archive.org/details/northseadiary00kingiala |publisher=London: Newnes |via=Internet Archive |ref={{sfnref|King-Hall}}}}
* {{Cite book |last=Mason |first=David |title=Duikbootoorlog. Onderzeeboten tegen konvooien |publisher=Standaard Uitgeverij |year=1994 |isbn=90-02-18166-3 |location=Antwerp |language=nl |ref={{sfnref|Mason}}}}
* {{cite book |last=Middlebrook |first=Martin |title=Convoy |publisher=Penguin Books |year=1976 |isbn=0-14-016695-5 |place= |oclc= |ref={{sfnref|Middlebrook}} |author-link=Martin Middlebrook}}
* {{Cite book |last=Miller |first=David |title=The illustrated directory of submarines of the world |date=2002 |publisher=Salamander |isbn=1840653752 |location=London}}
* {{cite book |last1=Möller |first1=Eberhard |title=The Encyclopedia of U-Boats |last2=Brack |first2=Werner |publisher=Chatham |year=2004 |isbn=1-85367-623-3 |location=London}}
* {{Cite book |last=Paterson |first=Lawrence |title=U-564 auf Feindfahrt – 70 Tage an Bord |publisher=Motorbuch Verlag |year=2005 |isbn=978-3-548-26664-0 |edition=3rd |location=Stuttgart |language=de |ref={{sfnref|Paterson}}}}
* {{Cite book |last=Paterson |first=Lawrence |title=Second U-Boat Flottila |publisher=Leo Cooper |year=2003 |isbn=0-85052-917-4 |edition= |location= |language= }}
* {{cite book |last=Rohwer |first=Jürgen |title=Chronology of the War at Sea, 1939–1945: The Naval History of World War Two |publisher=US Naval Institute Press |year=2005 |isbn=978-1-59114-119-8 |place=Annapolis |ref={{sfnRef|Rohwer}} |author-link=Jürgen Rohwer}}
* {{Cite book |last=Rössler |first=Eberhard |title=The U-boat : the evolution and technical history of German submarines |date=2001 |publisher=Casell |isbn=0304361208 |location=London}}
* {{Cite book |last=Showell |first=Jak Mallmann |title=The U-boat Century: German Submarine Warfare, 1906–2006 |year=2006 |publisher=Naval Institute Press |isbn=1-59114-892-8 |ref={{sfnref|Showell}}}}
* {{Cite book |last=Wragg |first=David W. |title=First World War at sea |publisher=Stroud |year=2014 |isbn=9780750955676}}

=== Online ===
* {{Cite web |title=ATROPO small submarine (1912) |url=https://www.navypedia.org/ships/italy/it_ss_atropo.htm |access-date=27 July 2025 |website=NAVYPEDIA |ref={{sfnref|Navypedia Atropo}}}}
* {{Cite web |title=U-Boot-Klasse 212 A |url=https://www.bundeswehr.de/de/ausruestung-technik-bundeswehr/seesysteme-bundeswehr/u-boot-klasse-212-a |access-date=23 March 2025 |website=Bundeswehr |ref={{sfnref|Bundeswehr}}}}
* {{cite web |url=https://www.naval-technology.com/projects/u212a-todaro-class-submarines/ |title=Naval Technology on the Todaro class |access-date=2019-03-09 |ref={{sfnref|NavTech Todaro}}}}
* {{Cite web |title=Invincible-Class Submarines |url=https://www.naval-technology.com/projects/invincible-class-submarines/ |access-date=23 March 2025 |website=Naval Technology |ref={{sfnref|NavTech Invincible}}}}
* {{Cite web |title=Reis class Type 214 New Type Submarine Project |url=https://www.globalsecurity.org/military/world/europe/tcg-ntsp.htm |access-date=24 March 2025 |website=GlobalSecurity |ref={{sfnref|GlobalSecurity Reiss}}}}
* {{Cite web |title=Type 214 / Type 209PN |url=https://www.globalsecurity.org/military/world/europe/type-214.htm |access-date=24 March 2025 |website=GlobalSecurity |ref={{sfnref|GlobalSecurity Type214/209PN}}}}
* {{Cite web |title=Type 216 |url=https://www.globalsecurity.org/military/world/europe/type-216.htm |access-date=24 March 2025 |website=GlobalSecurity |ref={{sfnref|GlobalSecurity Type216}}}}
* {{Cite web |title=Turkish Navy commissions first Reis-class AIP submarine TCG Piri Reis |url=https://www.navalnews.com/naval-news/2024/08/turkish-navy-commissions-first-reis-class-aip-submarine-tcg-piri-reis/ |access-date=24 March 2025 |website=NavalNews |date=25 August 2024 |ref={{sfnref|NavalNews}}}}

==Further reading==
*Abbatiello, John (2005) ''Anti-Submarine Warfare in World War I: British Naval Aviation and the Defeat of the U-Boats''
*Buchheim, Lothar-Günther. ''Das Boot'' (original German edition 1973, eventually translated into English and many other Western languages). [[Das Boot|Movie adaptation]] in 1981, directed by [[Wolfgang Petersen]]
*Gannon, Michael (1990) ''Operation Drumbeat''. Naval Institute Press. {{ISBN|978-1-59114-302-4}}
*Gray, Edwyn A. (1994) ''The U-Boat War, 1914–1918''
*Hans Joachim Koerver (2010) ''German Submarine Warfare 1914–1918 in the Eyes of British Intelligence'', LIS Reinisch, {{ISBN|978-3-902433-79-4}}
*Möller, Eberhard and Werner Brack (2006) ''The Encyclopedia of U-Boats: From 1904 to the Present'', {{ISBN|1-85367-623-3}}
* O'Connor, Jerome M. (June 2000) "Inside the Grey Wolves' Den". ''Naval History''. The US Naval Institute Author of the Year feature describes the building and operation of the German U-boat bases in France.
*Preston, Antony (2005) ''The World's Greatest Submarines''.
*Stern, Robert C. (1999) ''Battle Beneath the Waves: U-boats at war''. Arms and Armor/Sterling Publishing. {{ISBN|1-85409-200-6}}.
*van der Vat, Dan (1988) ''The Atlantic Campaign''. Harper & Row. Connects submarine and antisubmarine operations between World War I and World War II, and suggests a continuous war.
*Von Scheck, Karl. ''U122: The Diary of a U-boat Commander''. Diggory Press, {{ISBN|978-1-84685-049-3}}
*Georg von Trapp and Elizabeth M. Campbell (2007) ''To the Last Salute: Memories of an Austrian U-Boat Commander''
*Westwood, David (2005) ''U-Boat War: Doenitz and the evolution of the German Submarine Service 1935–1945'', {{ISBN|1-932033-43-2}}
*Werner, Herbert. ''[[Iron Coffins|Iron Coffins: A Personal Account of the German U-Boat Battles of World War II]]'', {{ISBN|978-0-304-35330-9}}

==External links==
{{Commons}}
* [https://archives-manuscripts.dartmouth.edu/repositories/2/resources/1917 U-112 and U-53 Submarine Collection] at Dartmouth College Library

{{Uboat}}
{{Warship types of the 19th & 20th centuries}}

{{authority control}}

{{DEFAULTSORT:U-Boat}}
[[Category:U-boat fiction]]
[[Category:U-boats| 01]]
[[Category:Submarines of Germany]]
[[Category:Submarines of the Imperial German Navy]]
[[Category:Submarines of the Kriegsmarine]]
[[Category:German Empire in World War I]]
[[Category:Germany in World War II]]
[[Category:Submarines by type]]
[[Category:World War I submarines]]
[[Category:World War II submarines]]