Fat Man was the plutonium bomb dropped on Nagasaki on August 9, 1945.
The bomb was an implosion-type nuclear weapon developed at Los Alamos Laboratory. It was carried by the B-29 bomber Bockscar and detonated over Nagasaki at 11:02 a.m. local time. Its design used a plutonium core compressed by surrounding conventional explosives.
Fat Man was the second nuclear weapon used in warfare. The first was Little Boy, a uranium gun-type bomb dropped on Hiroshima three days earlier. The two weapons used different nuclear materials and fundamentally different assembly methods.
The name is sometimes confused with Gadget, the experimental device tested at Trinity in New Mexico. Gadget was the first full-scale nuclear device, while Fat Man was the wartime weapon used at Nagasaki. The bombings, combined with Soviet entry into the war and Japan’s internal political crisis, preceded the surrender announcement on August 15.