Fat Man

"Fat Man" (also known as Mark III) is the codename for the type of nuclear bomb the United States detonated over the Japanese city of Nagasaki 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 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 Superfortress Bockscar piloted by Major Charles Sweeney.

Fat Man
Replica of the original Fat Man bomb
TypeNuclear weapon
Place of originUnited States
Production history
DesignerLos Alamos Laboratory
Produced1945–1949
No. built120
Specifications
Mass10,300 pounds (4,670 kg)
Length128 inches (3.3 m)
Diameter60 inches (1.5 m)

FillingPlutonium
Filling weight6.4 kg
Blast yield21 kt (88 TJ)

The name Fat Man refers to the early design of the bomb because it had a wide, round shape. 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 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Crossroads nuclear tests at Bikini Atoll in 1946, and some 120 were produced between 1947 and 1949, when it was superseded by the Mark 4 nuclear bomb.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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