 The Mark III Mod 0 Fat Man was ordered to be put 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. A new plant was established at the Iowa Army Ordnance 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 The Mod 0s were withdrawn from service between March and July 1949, and by October they had all been rebuilt as Mods 1 and 2. Some 120 Mark III Fat Man units were added to the stockpile between 1947 and 1949, when it was superseded by the Mark 4 nuclear bomb. The Mark III Fat Man was retired in 1950.
