June 27, 1944: Atomic Bomb Completes Testing

  • Published
  • U.S. Army Air Forces

A final test of the Fat Man’s internal parachute system completed the Project A aerodynamic test series of atomic weapons ballistic shapes. The Fat Man weapon was subsequently detonated over Hiroshima, Japan.

Fat Man was the code name for the nuclear bomb that was detonated over the Japanese city of Nagasaki by the United States on August 9, 1945. It was the second of the only two nuclear weapons ever used in warfare, the first being Little Boy, and its detonation marked the third nuclear explosion in history. It was built by scientists and engineers at Los Alamos Laboratory using plutonium from the Hanford Site, and it was dropped from the Boeing B-29 piloted by Major Charles Sweeney.

The name Fat Man refers to the early design of the bomb because it had a wide, round shape; it was also known as the Mark III. Fat Man was an implosion-type nuclear weapon with a solid plutonium core. The first of that type to be detonated was the Gadget in the Trinity nuclear test less than a month earlier on July 16, at the Alamogordo Bombing and Gunnery Range in New Mexico. Two more were detonated during the Operation Crossroads nuclear tests at Bikini Atoll in 1946, and some 120 were produced between 1947 and 1949, when it was superseded by the Mark 4 nuclear bomb. The Fat Man was retired in 1950.

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