Fat Man was the code name of the atomic bomb dropped on Nagasaki.
The United States dropped Fat Man on August 9, 1945, three days after Little Boy was used against Hiroshima. Fat Man was a plutonium implosion weapon, unlike Little Boy, which used a uranium gun-type design. The explosion devastated Nagasaki and caused extensive loss of life, although the exact total remains difficult to determine because of injuries, radiation, and later deaths.
The bomb was carried by the B-29 bomber Bockscar, piloted by Major Charles Sweeney. Its target was initially Kokura, but cloud cover and smoke led the crew to proceed to Nagasaki. The attack formed part of the final crisis that preceded Japan’s surrender announcement.
Fat Man is often confused with Little Boy because both were used in the same short period. Little Boy struck Hiroshima on August 6, while Fat Man struck Nagasaki on August 9. Japan announced acceptance of surrender terms several days later.