The codename of the atomic bomb dropped on Nagasaki before Japan’s 1945 surrender was Fat Man.
The United States dropped the plutonium-based weapon on Nagasaki on 9 August 1945, three days after Little Boy was used against Hiroshima. Fat Man was an implosion-type nuclear weapon, while Little Boy used a different gun-type design based on uranium-235.
The bomb was carried by the B-29 bomber Bockscar and detonated at approximately 11:02 a.m. local time. The intended target was affected by cloud and visibility conditions, so the bomb fell over the Urakami Valley rather than directly over the planned aiming point.
Japan announced its acceptance of the Allied surrender terms on 15 August, six days after the Nagasaki bombing. The formal surrender ceremony followed on 2 September aboard USS Missouri. Fat Man is sometimes confused with Little Boy because both weapons were used in the same final campaign, but their designs, materials, aircraft, and target cities were different.