Fat Man was the United States codename for the atomic bomb dropped on Nagasaki on 9 August 1945.
The bomb was a plutonium implosion weapon carried by the B-29 Bockscar, piloted by Major Charles Sweeney. Its intended target was Kokura, but poor visibility and smoke led the crew to proceed to the secondary target, Nagasaki. The weapon detonated over the city shortly after 11 a.m. local time.
Fat Man was different from Little Boy, the uranium gun-type bomb dropped on Hiroshima three days earlier. The two weapons used different designs and nuclear materials. The United States had also used “Gadget” for the experimental device tested at Trinity in July 1945.
Japan’s leaders were already confronting the Hiroshima attack and the Soviet entry into the war when Nagasaki was bombed. Emperor Hirohito later supported accepting the Potsdam terms, leading to Japan’s surrender announcement on 15 August and formal signing on 2 September.