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
393d Bomb Squadron atomic bomb delivery techniques. The squadron carried out two Atomic Bombing missions over Japan in August 1945, being the only squadron in the world to ever carry out and deliver nuclear weapons in combat. Dropped the first atomic bomb on Hiroshima, Japan, on 6 August 1945, and the second atomic bomb on Nagasaki, Japan, on 9 August 1945. Reassigned to the United States in November 1945, becoming part of Continental Air Forces (later Strategic Air Command). Deployed to Kwajalein in 1946 to carry out Operation Crossroads atomic bomb tests on Bikini Atoll in July. Began upgrading to the new Boeing