Editing Fat Man (section)

==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=http://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>