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{{Short description|U.S. atomic bomb type used at Nagasaki, 1945}}
{{about|the World War II nuclear weapon}}
{{pp|small=yes}}
{{good article}}
{{Use dmy dates|date=July 2024}}{{Use American English|date=July 2018}}
{{Infobox weapon
| name               = Fat Man
| image              = [[File:Fat Man (replica of nuclear bomb).jpg|300px]]
| caption            = Replica of the original Fat Man bomb
| type               = [[Nuclear weapon|Nuclear]] [[nuclear fission|fission]] [[gravity bomb]]
<!--Type selection-->| designer           = [[Los Alamos Laboratory]]
| number             = 120
<!--General specifications-->
<!--Note on units: Wikipedia policy is to use as the primary values the original units system and provide conversions from that to the other unit system. Changing the natively English units' values to metric as the base unit violates Wikipedia policy, as does removing them entirely.-->| length             = {{convert|128|in|m|1}}
| width              = 
| height             = 
| diameter           = {{convert|60|in|m}}
<!--Explosive specifications-->| origin             = United States
| is_explosive       = yes
<!--Production history-->| design_date        = 
| manufacturer       = 
| unit_cost          = 
| production_date    = 1945–1949
| weight             = {{convert|10300|lb|-1}}
| part_length        = 
| filling            = [[Plutonium]]
| filling_weight     = 6.2&nbsp;kg{{sfn|Coster-Mullen|2012|p=57}}
| detonation         = 
| yield              = {{cvt|21|kt(TNT)|TJ|lk=in}}
}}

"'''Fat Man'''" (also known as '''Mark III''') was the design of the [[nuclear weapon]] the United States used for seven of the first eight nuclear weapons ever detonated in history. It is also the most powerful design to ever be used in warfare.

A Fat Man device was [[Atomic bombings of Hiroshima and Nagasaki#Bombing of Nagasaki|detonated over the Japanese city of Nagasaki]] on 9 August 1945. It was the second and larger of the only two nuclear weapons ever used in warfare.  It was dropped from the [[Boeing B-29 Superfortress]] ''[[Bockscar]]'' piloted by Major [[Charles Sweeney]]. Its detonation marked the third nuclear explosion in history. The name Fat Man refers to the wide, round shape. Fat Man was an [[implosion-type nuclear weapon]] with a solid plutonium [[Nuclear reactor core|core]], and later with improved cores.

The first Fat Man to be detonated was "The Gadget" in the [[Trinity (nuclear test)|Trinity nuclear test]] less than a month earlier on 16 July at the [[Holloman Air Force Base|Alamogordo Bombing and Gunnery Range]] in [[New Mexico]].  It was built by scientists and engineers at [[Los Alamos Laboratory]] using [[plutonium]] manufactured at the [[Hanford Site]]. The second nuclear explosion, and the first used in warfare, was [[Little Boy]], a different device based on [[uranium]]. Two more Fat Mans were detonated during the [[Operation Crossroads]] nuclear tests at [[Bikini Atoll]] in 1946. The three tests in the next series, [[Operation Sandstone]] in 1948, used Fat Man devices with improved cores.  Fat Man was finally superseded by the [[Mark 4 nuclear bomb]] in the [[Operation Ranger]] tests.

==Early decisions==
[[Robert Oppenheimer]] held conferences in Chicago in June 1942,  and in [[Berkeley, California]], in July, at which various engineers and physicists discussed nuclear bomb design issues. They chose a [[Gun-type fission weapon|gun-type]] design in which two sub-critical masses would be brought together by firing a "bullet" into a "target".{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=42–44}} [[Richard C. Tolman]] suggested an [[implosion-type nuclear weapon]], but the proposal attracted little interest.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=55}}

The feasibility of a [[plutonium]] bomb was questioned in 1942. [[Wallace Akers]], the director of the British "[[Tube Alloys]]" project, told [[James Bryant Conant]] on 14 November that [[James Chadwick]] had "concluded that plutonium might not be a practical [[Fissile material|fissionable material]] for weapons because of impurities".{{sfn|Nichols|1987|pp=64-65}} Conant consulted [[Ernest Lawrence]] and [[Arthur Compton]], who acknowledged that their scientists at Berkeley and Chicago, respectively, knew about the problem, but they could offer no ready solution. Conant informed [[Manhattan Project]] director [[Brigadier General (United States)|Brigadier General]] [[Leslie R. Groves Jr.]], who in turn assembled a special committee consisting of Lawrence, Compton, Oppenheimer, and McMillan to examine the issue. The committee concluded that any problems could be overcome simply by requiring higher purity.{{sfn|Nichols|1987|pp=64–65}}

Oppenheimer reviewed his options in early 1943 and gave priority to the gun-type weapon,{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=55}} but he created the E-5 Group at the [[Los Alamos Laboratory]] under [[Seth Neddermeyer]] to investigate implosion as a hedge against the threat of pre-[[detonation]]. Implosion-type bombs were determined to be significantly more efficient in terms of explosive yield per unit mass of fissile material in the bomb, because compressed fissile materials react more rapidly and therefore more completely. Nonetheless, it was decided that the plutonium gun would receive the bulk of the research effort, since it was the project with the least uncertainty involved. It was assumed that the [[uranium]] gun-type bomb could be easily adapted from it.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=87}}

==Naming==
{{Further|Little Boy#Naming}}
The gun-type and implosion-type designs were codenamed "[[Thin Man (nuclear bomb)|Thin Man]]" and "Fat Man", respectively. These code names were created by [[Robert Serber]], a former student of Oppenheimer's who worked on the Manhattan Project. He chose them based on their design shapes; the Thin Man was a very long device, and the name came from the [[Dashiell Hammett]] detective novel ''[[The Thin Man]]'' and [[The Thin Man (film)|series of movies]]. The Fat Man was round and fat and was named after [[Sydney Greenstreet]]'s character in Hammett's ''[[The Maltese Falcon (1941 film)|The Maltese Falcon]]''. The [[Little Boy]] uranium gun-type design came later and was named only to contrast with the Thin Man.{{sfn|Serber|Crease|1998|p=104}} Los Alamos's Thin Man and Fat Man code names were adopted by the [[United States Army Air Forces]] in their involvement in the Manhattan Project, codenamed [[Silverplate]]. A cover story was devised that Silverplate was about modifying a [[Pullman (car or coach)|Pullman car]] for use by President [[Franklin Roosevelt]] (Thin Man) and United Kingdom Prime Minister [[Winston Churchill]] (Fat Man) on a secret tour of the United States.{{sfn|Bowen|1959|p=96}} Air Forces personnel used the code names over the phone to make it sound as though they were modifying a plane for Roosevelt and Churchill.{{sfn|Rhodes|1986|p=481}}

==Development==
Neddermeyer discarded Serber and Tolman's initial concept of implosion as assembling a series of pieces in favor of one in which a hollow sphere was imploded by an explosive shell. He was assisted in this work by [[Hugh Bradner]], [[Charles Critchfield]], and John Streib. [[L. T. E. Thompson]] was brought in as a consultant and discussed the problem with Neddermeyer in June 1943. Thompson was skeptical that an implosion could be made sufficiently symmetric. Oppenheimer arranged for Neddermeyer and [[Edwin McMillan]] to visit the [[National Defense Research Committee]]'s Explosives Research Laboratory near the [[Experimental Mine, U.S. Bureau of Mines|laboratories]] of the [[United States Bureau of Mines|Bureau of Mines]] in [[Bruceton, Pennsylvania]] (a [[Pittsburgh]] suburb), where they spoke to [[George Kistiakowsky]] and his team. But Neddermeyer's efforts in July and August at imploding tubes to produce cylinders tended to produce objects that resembled rocks. Neddermeyer was the only person who believed that implosion was practical, and only his enthusiasm kept the project alive.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=86–90}}

[[File:AirForceMuseum FatManReplica.jpg|upright=1.25|thumb|left|alt=Fat Man Replica|Replica mockup of a ''Fat Man'' displayed in the [[National Museum of the United States Air Force]], beside the ''[[Bockscar]]'' B-29 that dropped the original device – black liquid asphalt sealant was sprayed over the original bomb casing's seams, simulated on the mockup.]]
Oppenheimer brought [[John von Neumann]] to Los Alamos in September to take a fresh look at implosion. After reviewing Neddermeyer's studies, and discussing the matter with [[Edward Teller]], von Neumann suggested the use of high explosives in [[shaped charge]]s to implode a sphere, which he showed could not only result in a faster assembly of fissile material than was possible with the gun method, but greatly reduce the amount of material required because of the resulting higher density.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=130–133}} The idea that, under such pressures, the plutonium metal would be compressed came from Teller, whose knowledge of how dense metals behaved under heavy pressure was influenced by his pre-war theoretical studies of the [[Earth's core]] with [[George Gamow]].{{sfn|Teller|2001|pp=174–176}} The prospect of more-efficient nuclear weapons impressed Oppenheimer, Teller, and [[Hans Bethe]], but they decided that an expert on explosives would be required. Kistiakowsky's name was immediately suggested, and Kistiakowsky was brought into the project as a consultant in October.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=130–133}}

The implosion project remained a backup until April 1944, when experiments by [[Emilio G. Segrè]] and his P-5 Group at Los Alamos on the newly reactor-produced plutonium from the [[X-10 Graphite Reactor]] at [[Clinton Engineer Works|Oak Ridge]] and the [[B Reactor]] at the [[Hanford Site]] showed that it contained impurities in the form of the [[isotope]] [[plutonium-240]]. This has a far higher spontaneous fission rate and radioactivity than [[plutonium-239]]. The [[cyclotron]]-produced isotopes, on which the original measurements had been made, held much lower traces of plutonium-240. Its inclusion in reactor-bred plutonium appeared unavoidable. This meant that the spontaneous fission rate of the reactor plutonium was so high that pre-detonation was highly likely and that the bomb would blow itself apart during the initial formation of [[critical mass]], creating a "[[Fizzle (nuclear explosion)|fizzle]]."{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=228}} The distance required to accelerate the plutonium to speeds where pre--detonation would be less likely would need a gun barrel too long for any existing or planned bomber. The only way to use plutonium in a workable bomb was therefore implosion.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=240–244}}

The impracticability of a gun-type bomb using plutonium was agreed at a meeting in Los Alamos on 17 July 1944. All gun-type work in the Manhattan Project was re-directed towards the Little Boy, [[enriched uranium]] gun design, and the Los Alamos Laboratory was reorganized with almost all of the research focused on the problems of implosion for the Fat Man bomb.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=240–244}} The idea of using shaped charges as three-dimensional [[explosive lens]]es came from [[James L. Tuck]] and was developed by von Neumann.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=163}} The success of the bomb relied on absolute precision in all of the plates moving inward at the same time.{{sfn|Coster-Mullen|2012|p=110}} To overcome the difficulty of synchronizing multiple detonations, [[Luis Walter Alvarez|Luis Alvarez]] and [[Lawrence H. Johnston|Lawrence Johnston]] invented [[exploding-bridgewire detonator]]s to replace the less precise [[primacord]] detonation system.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=163}} [[Robert Christy]] is credited with doing the calculations that showed how a solid subcritical sphere of plutonium could be compressed to a critical state, greatly simplifying the task, since earlier efforts had attempted the more-difficult compression of a hollow spherical shell.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=270–271}} After Christy's report, the solid-plutonium core weapon was referred to as the "[[pit (nuclear weapon)#Christy pits|Christy Gadget]]".{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=293, 307–308}}

The task of the [[metallurgist]]s was to determine how to cast plutonium into a sphere. The difficulties became apparent when attempts to measure the density of plutonium gave inconsistent results. At first contamination was believed to be the cause, but it was soon determined that there were multiple [[allotropes of plutonium]].{{sfn|Hewlett|Anderson|1962|pp=244–245}} The brittle α phase that exists at room temperature changes to the plastic β phase at higher temperatures. Attention then shifted to the even more malleable δ phase that normally exists in the {{convert|300|-|450|C|round=5}} range. It was found that this was stable at room temperature when alloyed with aluminum, but aluminum emits neutrons when bombarded with [[alpha particle]]s, which would exacerbate the pre-ignition problem. The metallurgists then hit upon a [[plutonium–gallium alloy]], which stabilized the δ phase and could be [[hot pressing|hot pressed]] into the desired shape. They found it easier to cast hemispheres than spheres. The core consisted of two hemispheres with a ring with a triangular cross-section between them to keep them aligned and prevent jets forming. As plutonium was found to corrode readily, the sphere was coated with nickel.{{sfn|Baker|Hecker|Harbur|1983|pp=144–145}}<ref>{{cite web |publisher=Restricted Data: The Nuclear Secrecy Blog |last=Wellerstein |first=Alex |title=You don't know ''Fat Man'' |url=http://blog.nuclearsecrecy.com/2011/11/28/you-dont-know-fat-man/ |access-date=4 April 2014 |archive-date=7 April 2014 |archive-url=https://web.archive.org/web/20140407081651/http://blog.nuclearsecrecy.com/2011/11/28/you-dont-know-fat-man/ |url-status=live }}</ref>

[[File:Fat Man test unit being raised from the pit into the bomb bay of a B-29.jpg|thumb|left|A [[pumpkin bomb]] (Fat Man test unit) being raised from the pit into the bomb bay of a B-29 for bombing practice during the weeks before the attack on Nagasaki]]
The size of the bomb was constrained by the available aircraft, which were investigated for suitability by [[Norman Foster Ramsey Jr.|Norman Foster Ramsey]]. The only Allied bombers considered capable of carrying the Fat Man without major modification were the British [[Avro Lancaster]] and the American [[Boeing B-29 Superfortress]].{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=380–383}}{{sfn|Hansen|1995|pp=119–120}}{{sfn|Groves|1962|p=254}} British scientist [[James Chadwick]] advocated the Lancaster which had a limited range but had a larger single bomb bay; but this was less of a problem when the Fat Man replaced the long ({{convert|17|ft|m}} [[Thin Man (bomb)|Thin Man]].{{sfn|Nichols|1987|p=172}} At the time, the B-29 represented the epitome of bomber technology with significant advantages in [[maximum takeoff weight]], range, speed, flight ceiling, and survivability. Without the availability of the B-29, dropping the bomb would likely have been impossible. However, this still constrained the bomb to a maximum length of {{convert|11|ft}}, width of {{convert|5|ft}} and weight of {{convert|20000|lb}}. Removing the bomb rails allowed a maximum width of {{convert|5.5|ft}}.{{sfn|Hansen|1995|pp=119–120}}

Drop tests began in March 1944 and resulted in modifications to the Silverplate aircraft due to the weight of the bomb.{{sfn|Campbell|2005|pp=8–10}} High-speed photographs revealed that the tail fins folded under the pressure, resulting in an erratic descent. Various combinations of stabilizer boxes and fins were tested on the Fat Man shape to eliminate its persistent wobble until an arrangement dubbed a "California Parachute" was approved, a cubical open-rear tail box outer surface with eight radial fins inside of it, four angled at 45 degrees and four perpendicular to the line of fall holding the outer square-fin box to the bomb's rear end.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=380–383}} In drop tests in early weeks, the Fat Man missed its target by an average of {{convert|1857|ft|0}}, but this was halved by June as the bombardiers became more proficient with it.{{sfn|Hansen|1995|p=131}}

The early Y-1222 model Fat Man was assembled with some 1,500 bolts.{{sfn|Coster-Mullen|2012|p=52}}{{sfn|Hansen|1995|p=121}} This was superseded by the Y-1291 design in December 1944. This redesign work was substantial, and only the Y-1222 tail design was retained.{{sfn|Hansen|1995|p=121}} Later versions included the Y-1560, which had 72 detonators; the Y-1561, which had 32; and the Y-1562, which had 132. There were also the Y-1563 and Y-1564, which were practice bombs with no detonators at all.{{sfn|Hansen|1995|p=127}} The final wartime Y-1561 design was assembled with just 90 bolts.{{sfn|Coster-Mullen|2012|p=52}}
On 16 July 1945, a Y-1561 model Fat Man, known as the Gadget, was detonated in a [[nuclear weapons testing|test explosion]] at a remote site in [[New Mexico]], known as the "[[Trinity (nuclear test)|Trinity]]" test. It gave a yield of about {{convert|25|kt(TNT)}}.<ref>{{cite journal |last1=Selby |first1=Hugh D. |last2=Hanson |first2=Susan K. |last3=Meininger |first3=Daniel |last4=Oldham |first4=Warren J. |last5=Kinman |first5=William S. |last6=Miller |first6=Jeffrey L. |last7=Reilly |first7=Sean D. |last8=Wende |first8=Allison M. |last9=Berger |first9=Jennifer L. |last10=Inglis |first10=Jeremy |last11=Pollington |first11=Anthony D. |last12=Waidmann |first12=Christopher R. |last13=Meade |first13=Roger A. |last14=Buescher |first14=Kevin L. |last15=Gattiker |first15=James R. |last16=Vander Wiel |first16=Scott A. |last17=Marcy |first17=Peter W. |date=11 October 2021 |title=A New Yield Assessment for the Trinity Nuclear Test, 75 Years Later |journal=Nuclear Technology |issn=0029-5450 |issue=sup1 |volume=207 |pages=321–325 |doi=10.1080/00295450.2021.1932176 |s2cid=244134027 |doi-access=free |arxiv=2103.06258 |bibcode=2021NucTe.207S.321S }}</ref> Some minor changes were made to the design as a result of the Trinity test.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=377}} [[Philip Morrison]] recalled that "There were some changes of importance... The fundamental thing was, of course, very much the same."{{sfn|Coster-Mullen|2012|p=53}}<ref>The most significant change involved the use of an anti-jet ring within the plutonium pit, described earlier. In the Trinity Gadget, the possibility of a fine jet of neutrons going between the seams of the pit was avoided by adding some crumpled gold foil around the initiator. Additionally, in the Trinity Gadget, the pit was electroplated with silver, whereas with the later Fat Man bombs, nickel was used.</ref>
{{clear left}}

==Interior==
The bomb was {{convert|128.375|in|m}} long and {{convert|60.25|in|cm}} in diameter. It weighed {{convert|10265|lb}}.{{sfn|Coster-Mullen|2012|p=47}}

<gallery mode=packed heights=300>
File:Fat Man External.svg|Fat Man external schematic. <br>1. One of four AN 219 contact [[fuze]]s <br>2. ''Archie'' radar antenna <br>3. Plate with batteries (to detonate charge surrounding nuclear components) <br>4. ''X-Unit,'' a firing set placed near the charge <br>5. Hinge fixing the two ellipsoidal parts of the bomb <br>6. Physics package (see details below) <br>7. Plate with instruments (radars, baroswitches, and timers) <br>8. Barotube collector <br>9. ''California Parachute'' tail assembly ({{convert|0.20|in|adj=on|disp=sqbr}} aluminum sheet)
File:Fat Man Internal Components.png|Fat Man internal schematic
</gallery>

==Assembly==
[[File:Fat Man Detonation.png|thumb|Cross section of the Fat Man "physics package". See description and colors in this section for details.|440x440px]]
[[File:Fat Man Assembly Tinian 1945.jpg|thumb|right|Fat Man's "physics package" nuclear device about to be encased]]
[[File:Fat Man Assembled Tinian 1945.jpg|thumb|right|Fat Man on its transport carriage, with liquid asphalt sealant applied over the casing's seams]]
[[File:Atomic Bomb Pits - Tinian - panoramio (3).jpg|thumb|right|Preserved Tinian "bomb pit#2", where Fat Man was loaded aboard ''Bockscar'']]

The [[plutonium pit]]{{sfn|Coster-Mullen|2012|p=52}} was {{convert|3.62|in}} in diameter and contained an "Urchin" [[modulated neutron initiator]] that was {{convert|0.8|in}} in diameter. The [[depleted uranium]] [[Tamper (nuclear weapon)|tamper]] was an {{convert|8.75|in|mm|adj=mid|-diameter}} sphere, surrounded by a {{convert|0.125|in|mm|adj=mid|-thick}} shell of boron-impregnated plastic. The plastic shell had a {{convert|5|in|mm|adj=mid|-diameter}} cylindrical hole running through it, like the hole in a cored apple, in order to allow insertion of the pit as late as possible. The missing tamper cylinder containing the pit could be slipped in through a hole in the surrounding {{convert|18.5|in|mm|adj=mid|-diameter}} aluminum pusher.{{sfn|Coster-Mullen|2012|p=186}} The pit was warm to the touch, emitting 2.4 W/kg-Pu, about 15 W for the {{convert|6.19|kg|adj=on}} core.{{sfn|Coster-Mullen|2012|p=49}}

The explosion symmetrically compressed the plutonium to twice its normal density before the "Urchin" added [[free neutron]]s to initiate a [[nuclear fission|fission]] [[nuclear chain reaction|chain reaction]].{{sfn|Coster-Mullen|2012|p=45}}
* {{legend|#ffff00 |{{resize|98%|An [[exploding-bridgewire detonator]] simultaneously starts a [[detonation wave]] in each of the 32 tapered high-explosive columns (positioned around the explosive material at the face centers of a [[truncated icosahedron]],{{sfn|Coster-Mullen|2012|p=41}} a geometry popularly known from the pattern of common [[soccer ball]]s).}}}}
* {{legend|#cc6633 |{{resize|98%|The detonation wave (arrows) is initially [[wikt:convex|convex]] in the}}...}}
* {{legend|#d79563 |...{{resize|98%|faster explosive ([[Composition B]]: 60% [[RDX]], 40% [[Trinitrotoluene|TNT]]).{{sfn|Coster-Mullen|2012|p=41}} The [[wavefront]]s become [[wikt:Special:Search/concave|concave]] in the}}...}}
* {{legend|#ffcc99 |...{{resize|98%|slower explosive ([[Baratol (explosive)|Baratol]]: 70% [[barium nitrate]], 30% TNT).{{sfn|Coster-Mullen|2012|p=41}} The 32 waves then merge into a single spherical implosive shock-wave which hits the}}...}}
* {{legend|#d79563 |...{{resize|98%|inner charges' faster explosive ([[Composition B]]).{{sfn|Coster-Mullen|2012|p=186}}}}}}
* {{legend|#c6c6c6 |{{resize|98%|The medium-density [[aluminum]] "pusher" transfers the imploding shock-wave from the low-density explosive to the high-density uranium, minimizing undesirable [[turbulence]].{{sfn|Hansen|1995|pp=122–123}} The shock-wave then compresses the inner components, passing through a}}...}}
* {{legend|#0000ff |...{{resize|98%|[[boron]]-plastic shell intended to prevent pre-detonation of the bomb by stray neutrons.{{sfn|Hansen|1995|pp=122–123}} The shock-wave reaches the center of the bomb, where the...}}}}
* {{legend|#008000 |{{resize|98%|...[[beryllium]]–[[Polonium-210|<sup>210</sup>Po]] "Urchin" is crushed,{{sfn|Coster-Mullen|2012|p=48}} pushing the two metals together and thereby releasing a burst of [[neutron]]s into the compressed}}...}}
* {{legend|#ff0000 |{{resize|98%|...[[plutonium pit|pit]] of the [[nickel]]-plated [[plutonium–gallium alloy|delta-phase alloy]] of [[plutonium-239|<sup>239</sup>Pu]]–[[Plutonium-240|<sup>240</sup>Pu]]–[[gallium]] (96%–1%–3% by [[Concentration#Molarity|molarity]]).{{sfn|Coster-Mullen|2012|p=57}}<ref name=nukearchive>{{cite web |first=Carey |last=Sublette |title=Section 8.0 The First Nuclear Weapons |url=https://nuclearweaponarchive.org/Nwfaq/Nfaq8.html|date=3 July 2007 |work=Nuclear Weapons FAQ|access-date=29 August 2013}}</ref> A fission chain reaction then begins. The tendency of the fissioning pit to blow itself apart prematurely is reduced by the inward [[momentum]] of the}}...}}
* {{legend|#808080 |{{resize|98%|...natural-[[uranium]] "tamper" (inertial confinement). The tamper also [[neutron reflector|reflects neutrons]] back into the pit, accelerating the chain reaction. If and when sufficient [[fast neutron]]s are produced, the tamper itself undergoes fission, accounting for up to 30% of the [[nuclear weapon yield|weapon's yield]].<ref name="The Fat Man's Uranium" />}}}}

The result was the fission of about {{convert|1|kg}} of the {{convert|6.19|kg}} of plutonium in the pit, or about 16% of the fissile material present.{{sfn|Coster-Mullen|2012|p=46}}<ref>{{cite web |first=Alex |last=Wellerstein |date=23 December 2013 |title=Kilotons per kilogram |publisher= Restricted Data |url=https://blog.nuclearsecrecy.com/2013/12/23/kilotons-per-kilogram/ |access-date=9 December 2020}}</ref> The detonation released the energy equivalent to the detonation of {{convert|21|ktonTNT|disp=or}}.{{sfn|Malik|1985|p=25}} About 30% of the yield came from fission of the uranium tamper.<ref name="The Fat Man's Uranium">{{cite web |title=The Fat Man's Uranium |first=Alex |last=Wellerstein |date=10 November 2014 |publisher= Restricted Data |url=https://blog.nuclearsecrecy.com/2014/11/10/fat-mans-uranium/ |access-date=9 December 2020}}</ref>

==Bombing of Nagasaki==
{{main|Atomic bombings of Hiroshima and Nagasaki#Bombing of Nagasaki}}

===Assembly===
[[File:Nagasakibomb.jpg|thumb|Mushroom cloud after Fat Man exploded over [[Nagasaki]] on 9 August 1945]]
The first plutonium core was transported with its polonium-beryllium modulated neutron initiator in the custody of [[Project Alberta]] courier [[Raemer Schreiber]] in a magnesium field carrying case designed for the purpose by Philip Morrison. Magnesium was chosen because it does not act as a tamper.{{sfn|Coster-Mullen|2012|p=45}} It left [[Kirtland Air Force Base|Kirtland Army Air Field]] on a [[C-54]] transport aircraft of the [[509th Composite Group]]'s 320th Troop Carrier Squadron on 26 July and arrived at [[North Field (Tinian)|North Field]] on [[Tinian, Northern Mariana Islands|Tinian]] on 28 July. Three Fat Man high-explosive pre-assemblies (designated F31, F32, and F33) were picked up at Kirtland on 28 July by three B-29s: ''[[Luke the Spook]]'' and ''[[Laggin' Dragon]]'' from the 509th Composite Group's [[393d Bombardment Squadron]], and another from the [[216th Army Air Forces Base Unit]]. The cores were transported to North Field, arriving on 2 August, when F31 was partly disassembled in order to check all its components. F33 was expended near Tinian during a final rehearsal on 8 August. F32 presumably would have been used for a third attack or its rehearsal.{{sfn|Campbell|2005|pp=38–40}}

On 7 August, the day after the bombing of Hiroshima, [[Rear Admiral (United States)|Rear Admiral]] [[William R. Purnell]], [[Rear Admiral (United States)|Commodore]] [[William S. Parsons]], Tibbets, [[General (United States)|General]] [[Carl Spaatz]] and [[Major General (United States)|Major General]] [[Curtis LeMay]] met on Guam to discuss what should be done next.{{sfn|Russ|1990|pp=64–65}} Since there was no indication of Japan surrendering,{{sfn|Frank|1999|pp=283–284}} they decided to proceed with their orders and drop another bomb. Parsons said that Project Alberta would have it ready by 11 August, but Tibbets pointed to weather reports indicating poor flying conditions on that day due to a storm and asked if the bomb could be made ready by 9 August. Parsons agreed to try to do so.{{sfn|Russ|1990|pp=64–65}}{{sfn|Groves|1962|p=342}}

Fat Man F31 was assembled on Tinian by Project Alberta personnel,{{sfn|Campbell|2005|pp=38–40}} and the physics package was fully assembled and wired. It was placed inside its ellipsoidal aerodynamic bombshell, which was painted mustard yellow, and wheeled out, where it was signed by nearly 60 people, including Purnell, Brigadier General [[Thomas F. Farrell]], and Parsons.{{sfn|Coster-Mullen|2012|p=67}}<ref name=":0">{{Cite magazine |last=Wellerstein |first=Alex |date=2015-08-07 |title=What About Nagasaki? |url=https://www.newyorker.com/tech/annals-of-technology/nagasaki-the-last-bomb |access-date=2024-07-28 |magazine=The New Yorker |language=en-US |issn=0028-792X}}</ref> The acronym "JANCFU" was stenciled on the bomb's nose, standing for "Joint Army-Navy-Civilian Fuckup", a play on the acronym "[[SNAFU]]".<ref name=":0" /><ref>{{Cite web |title=World War II: the battle for Kiska (pt 2). - Free Online Library |url=https://www.thefreelibrary.com/World+War+II:+the+battle+for+Kiska+(pt+2)-a030243144 |access-date=28 July 2024 |website=www.thefreelibrary.com |quote=It was the Battle of Kiska that would lead Time magazine to create the acronym, JANFU (joint army-navy foul-up) to complement the earlier SNAFU (situation normal, all fouled-up).}}</ref><ref>{{Cite journal |first1=Ellen |last1=Bradbury |first2=Sandra |last2=Blakeslee |date=5 August 2022 |title=The harrowing story of the Nagasaki bombing mission |url=https://thebulletin.org/2022/08/harrowing-story-of-the-nagasaki-bombing-mission/ |access-date=28 July 2024 |journal=Bulletin of the Atomic Scientists |quote=It even had a code: JANCFU for "joint army navy combined foul up" which was a cousin of "SNAFU", military vernacular for "situation normal, all f***ed up."}}</ref> It was then wheeled to the [[bomb bay]] of the B-29 Superfortress named ''[[Bockscar]]''<!-- yes, it is "Bockscar" not "Bock's Cr". This is ''not'' a typo! --> after the plane's command pilot Captain [[Frederick C. Bock]],<ref>{{cite web|url=https://awesometalks.wordpress.com/2008/08/07/bockscar-the-forgotten-plane-that-dropped-the-atomic-bomb/ |title=Bockscar … The Forgotten Plane That Dropped The Atomic Bomb « A Little Touch of History |date=7 August 2008 |publisher=Awesometalks.wordpress.com |access-date=31 August 2012}}</ref> who flew ''[[The Great Artiste]]'' with his crew on the mission. ''Bockscar'' was flown by Major [[Charles W. Sweeney]] and his crew, with Commander [[Frederick L. Ashworth]] from Project Alberta as the weaponeer in charge of the bomb.{{sfn|Campbell|2005|p=32}}

===Detonation===
{{See also|Weather events during wars#World War II}}
[[File:Nagasaki509th 1.gif|thumb|right|Detonation of the Mark III 'Fat Man' and ensuing mushroom cloud.]]
[[File:Nagasaki509th 2.gif|thumb|right]]
[[File:Hypocenter_of_Atomic_bombings_in_Nagasaki.jpg|265x265px|right|thumb|[[Hypocenter]] of Fat Man Atomic bomb in Nagasaki]]
''Bockscar'' lifted off at 03:47 on 9 August 1945, with [[Kokura]] as the primary target and [[Nagasaki]] the secondary target. The weapon was already armed but with the green electrical safety plugs still engaged. Ashworth changed them to red after ten minutes so that Sweeney could climb to {{convert|17000|ft}} in order to get above storm clouds.{{sfn|Rhodes|1986|p=740}} During the pre-flight inspection of ''Bockscar'', the flight engineer notified Sweeney that an inoperative fuel transfer pump made it impossible to use {{convert|640|USgal|L}} of fuel carried in a reserve tank. This fuel would still have to be carried all the way to Japan and back, consuming still more fuel. Replacing the pump would take hours; moving the Fat Man to another aircraft might take just as long and was dangerous as well, as the bomb was live. Colonel [[Paul Tibbets]] and Sweeney therefore elected to have ''Bockscar'' continue the mission.{{sfn|Sweeney|Antonucci|Antonucci|1997|pp=204–205}}

[[File:Nagasaki 1945 - Before and after (adjusted).jpg|thumb|right|Effects of the Fat Man's detonation on Nagasaki]]
Kokura was obscured by clouds and drifting smoke from fires started by a major [[firebombing]] raid by 224 B-29s on nearby [[Yahata, Fukuoka|Yahata]] the previous day. This covered 70% of the area over Kokura, obscuring the aiming point. Three bomb runs were made over the next 50 minutes, burning fuel and repeatedly exposing the aircraft to the heavy defenses of Yahata, but the bombardier was unable to drop visually. By the time of the third bomb run, Japanese [[Anti-aircraft warfare|anti-aircraft fire]] was getting close; Second Lieutenant [[Jacob Beser]] was monitoring Japanese communications, and he reported activity on the Japanese fighter direction radio bands.{{sfn|Sweeney|Antonucci|Antonucci|1997|pp=179, 213–215}}

Sweeney then proceeded to the alternative target of Nagasaki. It was obscured by clouds as well, and Ashworth ordered Sweeney to make a radar approach. At the last minute, however, bombardier{{sfn|Rhodes|1986|p=740}} Captain [[Kermit K. Beahan]]{{sfn|Campbell|2005|p=32}} found a hole in the clouds. The Fat Man was dropped and exploded at 11:02 local time, following a 43-second free-fall, at an altitude of about {{convert|1650|ft}}.{{sfn|Rhodes|1986|p=740}} 

An estimated 35,000–40,000 people were killed outright by the bombing at Nagasaki. A total of 60,000–80,000 fatalities resulted, including from long-term health effects, the strongest of which was leukemia with an attributable risk of 46% for bomb victims.<ref>[http://k1project.org/explore-health/hiroshima-and-nagasaki-the-long-term-health-effects Columbia university center for nuclear studies: Hiroshima and Nagasaki: The Long Term Health Effects] {{webarchive |url=https://web.archive.org/web/20150723042220/http://k1project.org/explore-health/hiroshima-and-nagasaki-the-long-term-health-effects |date=23 July 2015 }}, updated 7/3/2014</ref> Others died later from related blast and burn injuries, and hundreds more from radiation illnesses from exposure to the bomb's initial radiation.{{sfn|Craven|Cate|1953|pp=723–725}} Most of the direct deaths and injuries were among munitions or industrial workers.<ref name="HOG">{{cite book |title=Nuke-Rebuke: Writers & Artists Against Nuclear Energy & Weapons (The Contemporary anthology series) |pages=22–29 |date=1 May 1984 |publisher=The Spirit That Moves Us Press}}</ref>

Mitsubishi's industrial production in the city was severed by the attack; the dockyard would have produced at 80 percent of its full capacity within three to four months, the steelworks would have required a year to get back to substantial production, the electric works would have resumed some production within two months and been back at capacity within six months, and the arms plant would have required 15 months to return to 60 to 70 percent of former capacity. The Mitsubishi-Urakami Ordnance Works, which manufactured the [[Type 91 torpedo]]es released in the [[attack on Pearl Harbor]], was destroyed in the blast.<ref name="HOG"/><ref>{{cite web |publisher=U.S. Strategic Bombing Survey |title=United States Strategic Bombing Survey Summary Report (Pacific War) The Effects of the Atomic Bombs |url=https://www.anesi.com/ussbs01.htm#teotab |page=24}}</ref>

==Post-war development==
[[File:Crossroads Baker.gif|right|thumb|Crossroads-''Baker'', 23-kilotons.]]
After the war, two Y-1561 Fat Man bombs were used in the [[Operation Crossroads]] nuclear tests at [[Bikini Atoll]] in the Pacific. The first was known as ''Gilda'' after [[Rita Hayworth]]'s character in the 1946 movie ''[[Gilda (film)|Gilda]],'' and it was dropped by the B-29 ''[[Big Stink (aircraft)|Dave's Dream]]''; it missed its aim point by {{convert|710|yd}}. The second bomb was nicknamed ''Helen of Bikini'' and was placed without its tail fin assembly in a steel caisson made from a submarine's conning tower; it was detonated {{convert|90|ft|m|0}} beneath the landing craft [[USS LSM-60|USS ''LSM-60'']]. The two weapons yielded about {{convert|23|kt(TNT)}} each.{{sfn|Coster-Mullen|2012|pp=84–85}}

The Los Alamos Laboratory and the Army Air Forces had already commenced work on improving the design. The [[North American B-45 Tornado]], [[Convair XB-46]], [[Martin XB-48]], and [[Boeing B-47 Stratojet]] bombers had bomb bays sized to carry the [[Grand Slam (bomb)|Grand Slam]], which was much longer but not as wide as the Fat Man. The only American bombers that could carry the Fat Man were the B-29 and the [[Convair B-36]]. In November 1945, the Army Air Forces asked Los Alamos for 200 Fat Man bombs, but there were only two sets of plutonium cores and high-explosive assemblies at the time. The Army Air Forces wanted improvements to the design to make it easier to manufacture, assemble, handle, transport, and stockpile. The wartime [[Project W-47]] was continued, and drop tests resumed in January 1946.{{sfn|Hansen|1995|pp=137–142}}

[[File:SandstoneYoke.gif|right|thumb|Sandstone-''Yoke'', 49-kilotons; utilized a newly designed 'levitated-pit' to increase yield efficiency.]]
The Mark III Mod 0 Fat Man was ordered into production in mid-1946. High explosives were manufactured by the [[Salt Wells Pilot Plant]], which had been established by the Manhattan Project as part of [[Project Camel]], and a new plant was established at the [[Iowa Army Ammunition Plant]]. Mechanical components were made or procured by the [[Rock Island Arsenal]]; electrical and mechanical components for about 50 bombs were stockpiled at Kirtland Army Air Field by August 1946, but only nine plutonium cores were available. Production of the Mod 0 ended in December 1948, by which time there were still only 53 cores available. It was replaced by improved versions known as Mods 1 and 2 which contained a number of minor changes, the most important of which was that they did not charge the X-Unit firing system's capacitors until released from the aircraft. The Mod 0s were withdrawn from service between March and July 1949, and by October they had all been rebuilt as Mods 1 and 2.{{sfn|Hansen|1995|pp=142–145}} Some 120 Mark III Fat Man units were added to the stockpile between 1947 and 1949,{{sfn|Coster-Mullen|2012|p=87}} when it was superseded by the [[Mark 4 nuclear bomb]].{{sfn|Hansen|1995|p=143}} The Mark III Fat Man was retired in 1950.{{sfn|Coster-Mullen|2012|p=87}}{{sfn|Hansen|1995|p=150}}

[[File:Casing for the first Soviet atomic bomb, RDS-1.jpg|right|thumb|Espionage information procured by [[Klaus Fuchs]], [[Theodore Hall]], and [[David Greenglass]] led to the first Soviet device "[[Joe 1|RDS–1]]" (above), which closely resembled Fat Man, even in its external shape.]] 

A nuclear strike would have been a formidable undertaking in the post-war 1940s due to the limitations of the Mark III Fat Man. The lead-acid batteries which powered the fuzing system remained charged for only 36 hours, after which they needed to be recharged. To do this meant disassembling the bomb, and recharging took 72 hours. The batteries had to be removed in any case after nine days or they corroded. The plutonium core could not be left in for much longer, because its heat damaged the high explosives. Replacing the core also required the bomb to be completely disassembled and reassembled. This required about 40 to 50 men and took between 56 and 72 hours, depending on the skill of the bomb assembly team, and the [[Armed Forces Special Weapons Project]] had only three teams in June 1948. The only aircraft capable of carrying the bomb were Silverplate B-29s, and the only group equipped with them was the 509th Bombardment Group at [[Walker Air Force Base]] in [[Roswell, New Mexico]]. They would first have to fly to [[Sandia Base]] to collect the bombs and then to an overseas base from which a strike could be mounted.{{sfn|Hansen|1995|pp=147–149}} In March 1948, during the [[Berlin Blockade]], all the assembly teams were in [[Enewetak Atoll|Eniwetok]] for the [[Operation Sandstone]] test, and the military teams were not yet qualified to assemble atomic weapons.{{sfn|Nichols|1987|pp=260,264,265}}

In June 1948, General [[Omar Bradley]], Major General [[Alfred Gruenther]] and Brigadier General [[Anthony McAuliffe]] visited Sandia and Los Alamos to be shown the "special requirements" of atomic weapons.  Gruenther asked Brigadier General [[Kenneth Nichols]] (hosting): "When are you going to show us the real thing? Surely this laboratory monstrosity is not the only type of atomic bomb we have in stockpile?"{{sfn|Nichols|1987|p=264}} Nichols told him that better weapons would soon become available. After the "astonishingly good" results of Operation Sandstone were available, stockpiling of improved weapons began.{{sfn|Nichols|1987|p=264}}

The Soviet Union's first nuclear weapon was based closely on Fat Man's design thanks to spies [[Klaus Fuchs]], [[Theodore Hall]], and [[David Greenglass]], who provided them with secret information concerning the Manhattan Project and Fat Man. It was detonated on 29 August 1949 as part of [[RDS-1|Operation "First Lightning"]].<ref>{{cite magazine|url=https://www.smithsonianmag.com/history/spies-who-spilled-atomic-bomb-secrets-127922660/|title=Spies Who Spilled Atomic Bomb Secrets|magazine=Smithsonian |first=Marian Smith |last=Holmes |date=19 April 2009 |access-date=5 April 2019}}</ref><ref>{{cite journal |last=Holloway |first=David |year=1993 |title=Soviet Scientists Speak Out |journal=Bulletin of the Atomic Scientists |volume=49 |issue=4 |pages=18–19 |doi=10.1080/00963402.1993.11456340 |bibcode=1993BuAtS..49d..18H |url=https://books.google.com/books?id=qQwAAAAAMBAJ&pg=PA18}}</ref><ref>{{cite web |url=https://www.nuclearweaponarchive.org/Nwfaq/Nfaq8.html#nfaq8.1.1 |title=Section 8.1.1 The Design of Gadget, Fat Man, and "Joe 1" (RDS-1)|first=Carey|last=Sublette |date=3 July 2007 |work=Nuclear Weapons FAQ |access-date=12 August 2011}}</ref>

==Notes==
{{reflist}}

==References==
{{refbegin}}
* {{cite journal |last1=Baker |first1=Richard D. |last2=Hecker |first2=Siegfried S. |last3=Harbur |first3=Delbert R. |title=Plutonium: A Wartime Nightmare but a Metallurgist's Dream |url=http://library.lanl.gov/cgi-bin/getfile?07-16.pdf |journal=[[Los Alamos Science]] |issue=Winter/Spring |year=1983 |pages=142–151 |access-date=22 November 2010 }}
* {{cite book |last=Bowen |first=Lee |title=Vol. I, Project Silverplate 1943–1946 |series=The History of Air Force Participation in the Atomic Energy Program, 1943–1953 |year=1959 |location=Washington, D.C. |publisher=U.S. Air Force, Air University Historical Liaison Office |url=http://www.foia.af.mil/shared/media/document/afd-091021-044.pdf |access-date=28 July 2013|url-status=dead |archive-url=https://web.archive.org/web/20140222001701/http://www.foia.af.mil/shared/media/document/afd-091021-044.pdf |archive-date=22 February 2014 }}
* {{cite book |last=Campbell |first=Richard H. |year=2005 |title=The Silverplate Bombers: A History and Registry of the Enola Gay and Other B-29s Configured to Carry Atomic Bombs |location=Jefferson, North Carolina |publisher=McFarland & Company |isbn= 978-0-7864-2139-8 |oclc=58554961 }}
* {{cite book |last=Coster-Mullen |first=John |title=Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man |location=Waukesha, Wisconsin |publisher=J. Coster-Mullen |year=2012 |asin=B0006S2AJ0 |oclc=298514167 }}
* {{cite book |editor-last=Craven |editor-first=Wesley |editor2-last=Cate |editor2-first=James |title= The Pacific: Matterhorn to Nagasaki |publisher= The University of Chicago Press |location= Chicago |year= 1953 |series= The Army Air Forces in World War II |url= https://www.ibiblio.org/hyperwar/AAF/V/index.html |oclc= 256469807 }}
* {{cite book |last = Groves |first = Leslie |author-link = Leslie Groves |title = Now It Can Be Told: The Story of the Manhattan Project |url = https://archive.org/details/nowitcanbetolds00grov |url-access = registration |location = New York |publisher = Harper |year = 1962 |isbn = 0-306-70738-1 |oclc = 537684 }}
* {{cite book | last = Frank | first = Richard B. | author-link = Richard B. Frank | title = Downfall: The End of the Imperial Japanese Empire | year = 1999 | publisher = Random House | location = New York | isbn =978-0-679-41424-7 }}
* {{cite book |last=Hansen |first=Chuck |author-link=Chuck Hansen |series=Swords of Armageddon: US Nuclear Weapons Development since 1945 |title=Volume V: US Nuclear Weapons Histories |location=Sunnyvale, California |publisher=Chukelea Publications |year= 1995 |isbn=978-0-9791915-0-3|oclc=231585284 }}
* {{cite book |last1=Hewlett |first1=Richard G. |author-link=Richard G. Hewlett |last2=Anderson |first2=Oscar E. |title=The New World, 1939–1946 |location=University Park |publisher=Pennsylvania State University Press |year=1962 |url=https://www.governmentattic.org/5docs/TheNewWorld1939-1946.pdf |archive-url=https://web.archive.org/web/20120227010123/http://www.governmentattic.org/5docs/TheNewWorld1939-1946.pdf |archive-date=2012-02-27 |url-status=live |access-date=26 March 2013 |isbn=978-0-520-07186-5 |oclc=637004643 }}
* {{cite book |last1=Hoddeson |first1=Lillian |author-link=Lillian Hoddeson |first2=Paul W. |last2=Henriksen |first3=Roger A. |last3=Meade |first4=Catherine L. |last4=Westfall |author4-link=Catherine Westfall |title=Critical Assembly: A Technical History of Los Alamos During the Oppenheimer Years, 1943–1945 |location=New York |publisher=Cambridge University Press |year=1993 |isbn=978-0-521-44132-2 |oclc=26764320 |url-access=registration |url=https://archive.org/details/criticalassembly0000unse }}
* {{cite web |last=Malik |first=John |archive-url=https://web.archive.org/web/20080227053729/http://www.mbe.doe.gov/me70/manhattan/publications/LANLHiroshimaNagasakiYields.pdf |archive-date=27 February 2008 |publisher=Los Alamos National Laboratory |id=LA-8819 |page=16 |title=The yields of the Hiroshima and Nagasaki nuclear explosions |date=September 1985 |url=http://www.mbe.doe.gov/me70/manhattan/publications/LANLHiroshimaNagasakiYields.pdf |access-date=27 February 2008 }}
* {{cite book |last=Nichols |first=Kenneth D. |author-link= Kenneth Nichols |title= The Road to Trinity |url= https://achive.org/details/roadtotrinity0000nich |url-access= registration |year= 1987 |publisher= William Morrow and Company |location= New York |isbn= 978-0-688-06910-0 |oclc= 15223648 }}
* {{cite book |last=Rhodes |first=Richard |author-link=Richard Rhodes |year=1986 |title=The Making of the Atomic Bomb |url=https://archive.org/details/makingofatomicbo00rhod |url-access=registration |location=New York |publisher=Simon & Schuster |isbn=978-0-684-81378-3 |oclc=13793436 }}
* {{cite book | last = Russ | first = Harlow W. | title = Project Alberta: The Preparation of Atomic Bombs For Use in World War II | year = 1990 | location = Los Alamos, New Mexico | publisher = Exceptional Books | isbn = 978-0-944482-01-8 | oclc = 24429257 }}
* {{cite book |last1=Serber |first1=Robert |author-link=Robert Serber |first2=Robert P. |last2=Crease |title=Peace & War: Reminiscences of a Life on the Frontiers of Science |location=New York |publisher=Columbia University Press |year=1998 |isbn=9780231105460 |oclc=37631186 |url=https://archive.org/details/peacewarreminisc00serb }}
* {{cite book |last1=Sweeney |first1=Charles |author-link=Charles Sweeney |first2=James A. |last2=Antonucci |first3=Marion K.
 |last3=Antonucci |title= War's End: An Eyewitness Account of America's Last Atomic Mission |publisher= Quill Publishing |year= 1997 |isbn= 978-0-380-78874-3 }}
* {{cite book |last=Teller |first=Edward |author-link=Edward Teller |title=Memoirs: A Twentieth-Century Journey in Science and Politics |location=Cambridge, Massachusetts |publisher=Perseus Publishing |year=2001 |isbn=9780738205328 |oclc=48150267 |url=https://archive.org/details/memoirstwentieth0000tell }}
{{refend}}

==See also==
* [[Third Shot]], a Fat Man-type weapon intended for a third Japanese target after Nagasaki

==External links==
{{Commons}}
* [https://web.archive.org/web/20120927090319/http://www.history.army.mil/html/books/011/11-10/CMH_Pub_11-10.pdf Manhattan: The Army and the Atomic Bomb]
* {{YouTube|id=Z9v5sW6t0zI|title=Video footage of the bombing of Nagasaki (silent)}}
* [https://www.atomicarchive.com/Movies/Movie3.shtml Fat Man Model] in QuickTime VR format
* {{Cite magazine |last=Samuels |first=David |orig-year=15 December 2008 |date=23 January 2009|title=Atomic John: A truck driver uncovers secrets about the first nuclear bombs |url=https://www.newyorker.com/reporting/2008/12/15/081215fa_fact_samuels |department=A Reporter at Large (column) |magazine=[[The New Yorker]] |ref=none}} Essay and interview with John Coster-Mullen, the author of ''Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man'', 2003 (first printed in 1996, self-published), considered a definitive text about Fat Man; illustrations from which are used in the [[Fat Man#Physics package|Physics Package]] section above.

{{United States nuclear devices}}
{{Manhattan Project}}
{{Portal bar|Nuclear technology|History of science}}

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