Nuclear fission the Manhattan Project during World War II (September 1, 1939 – September 2, 1945) carried out most of the early scientific work on fission chain reactions, culminating in the three events involving fission bombs that occurred during the war. The first fission bomb, codenamed "The Gadget", was detonated during the Trinity Test in the desert of New Mexico on July 16, 1945. Two other fission bombs, codenamed "Little Boy" and "Fat Man", were used in combat against the Japanese cities of Hiroshima and Nagasaki in on August 6 and 9, 1945 respectively. Even the first fission bombs were thousands of
Mark 7 nuclear bomb Mark 7 nuclear bomb Mark 7 "Thor" (or Mk-7') was the first tactical fission bomb adopted by US armed forces. It was also the first weapon to be delivered using the toss method with the help of the low-altitude bombing system (LABS). The weapon was tested in Operation Buster-Jangle. To facilitate external carry by fighter-bomber aircraft, Mark 7 was fitted with retractable stabilizer fins. The Mark 7 warhead (W7) also formed the basis of the BOAR rocket, the Mark 90 Betty nuclear depth charge, MGR-1 Honest John rocket, and MGM-5 Corporal ballistic missile. It was also supplied for delivery by