Fat Man was the code name of the atomic bomb dropped on Nagasaki before Japan formally surrendered in 1945.
The United States dropped Fat Man on August 9, 1945, three days after Little Boy had been used against Hiroshima. Fat Man was an implosion-type weapon using a plutonium core, making it technically more complex than the uranium gun-type Little Boy.
The B-29 Bockscar carried the bomb from Tinian. Kokura was the primary target, but cloud cover and fuel concerns led the crew toward the secondary target, Nagasaki. A break in the clouds allowed the bombardier to make a visual approach, and the bomb detonated at about 11:02 a.m. local time.
Fat Man had an estimated yield of approximately 21 kilotons of TNT. Nagasaki’s hilly terrain limited some of the blast’s reach, but the attack still caused catastrophic destruction and loss of life. Japan announced its acceptance of the Allied surrender terms six days later.