All of the nuclear weapons available in WW2 were owned by the US and were pure fission atomic bombs:
- 'Gadget', MK-III prototype plutonium implosion assembly design, tested on a 100 foot tower at Trinity site, NM on July 16, 1945
- 'Little Boy', MK-I uranium gun assembly design, dropped by the B-29 Enola Gay on Hiroshima on August 6, 1945
- 'Fatman', MK-III plutonium implosion assembly design, dropped by the B-29 Bockscar on Nagasaki on August 9, 1945
- unnamed, MK-III plutonium implosion assembly design, arrived in San Francisco on August 18, 1945 to be flown to Tinian then dropped on Japan in late August 1945 but was returned to Los Alamos
Had the war not ended the US had plans and the industrial capacity to make 20 more atomic bombs and drop them on Japan:
- 3 MK-III plutonium implosion assembly design for September 1945
- 3 MK-III plutonium implosion assembly design for October 1945
- 7 modified MK-III composite plutonium/uranium implosion assembly design for November 1945
- 7 modified MK-III composite plutonium/uranium implosion assembly design for December 1945
Early planning had proposed additional production of the MK-I uranium gun assembly design, but after the successful July 16, 1945 Trinity test shot this was canceled, as it was decided the uranium could be used more efficiently in the modified MK-III composite plutonium/uranium core design. The 'Little Boy' was already in transit to Tinian aboard the Indianapolis at the time of this test, so it was used.
