Fat Man

Fat Man
Replica of the original Fat Man bomb
Type	Nuclear weapon
Place of origin	United States
Production history
Designer	Los Alamos Laboratory
Produced	1945–1949
Number built	120
Specifications
Weight	10,300 pounds (4,670 kg)
Length	128 inches (3.3 m)
Diameter	60 inches (1.5 m)
Filling	Plutonium
Filling weight	14 pounds (6.4 kg)
Blast yield	21 kt (88 TJ; 1 g mass equivalent)

"Fat Man" was the codename for the atomic bomb that was detonated over the Japanese city of Nagasaki by the United States on 9 August 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-ever man-made nuclear explosion in history. It was built by scientists and engineers at Los Alamos Laboratory using plutonium from the Hanford Site and dropped from the Boeing B-29 Superfortress Bockscar. For the Fat Man mission, Bockscar was piloted by Major Charles W. Sweeney.

The name Fat Man refers generically 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 16 July at the Alamogordo Bombing and Gunnery Range in New Mexico.

Two more Fat Man bombs were detonated during the Operation Crossroads nuclear tests at Bikini Atoll in 1946. Some 120 Fat Man units were produced between 1947 and 1949, when it was superseded by the Mark 4 nuclear bomb. The Fat Man was retired in 1950.

In 1942, prior to the Army taking over wartime atomic research, Robert Oppenheimer held conferences in Chicago in June and Berkeley, California, in July, at which various engineers and physicists discussed nuclear bomb design issues. A gun-type design was chosen, in which two sub-critical masses would be brought together by firing a "bullet" into a "target".Richard C. Tolman suggested an implosion-type nuclear weapon, but the idea attracted scant consideration.