Nagasaki was hit by the Fat Man atomic bomb on August 9, 1945.
The United States dropped Fat Man from the B-29 bomber Bockscar. It was a plutonium implosion weapon, technically different from Little Boy, the uranium gun-type bomb dropped on Hiroshima three days earlier.
Nagasaki was the secondary target for the mission. The original target was Kokura, but cloud cover and smoke obscured the aiming point, so the aircraft proceeded to Nagasaki. The bomb detonated over the Urakami Valley, an industrial area containing factories, shipyards, and other wartime facilities.
The bombing occurred on the same day that the Soviet Union declared war on Japan and invaded Japanese-held Manchuria. Japan announced its surrender six days later, on August 15, though historians continue to debate the relative importance of the atomic bombings, Soviet entry, and other factors in the decision.