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
B41 nuclear bomb ever deployed by the United States, with a maximum yield of 25 megatons (Mt), and weighing in at . It remains the highest yield-to-weight ratio of any weapon created. The US claimed in 1963 that it could produce a 35 Mt fusion bomb, and put it on a Titan II ( payload), almost doubling the yield-to-weight ratio of the B-41. The B-41 was of the usual long cylindrical shape. The nuclear fusion warhead was of the Teller-Ulam type and used a 40–100 kiloton implosion type nuclear fission primary (reportedly based on the "Smokey" TX-41 shot of Operation Plumbbob) fueled by