Nagasaki was struck by the second atomic bomb used in World War II before Japan surrendered.
The United States dropped the plutonium implosion bomb known as Fat Man on Nagasaki on August 9, 1945. The first atomic bomb, Little Boy, had been dropped on Hiroshima three days earlier, on August 6.
Nagasaki was not the original primary target that morning. Kokura had been designated the main target, but cloud cover and smoke obstructed visibility, so the aircraft proceeded to its secondary target, Nagasaki. The bomb detonated over the Urakami Valley, an industrial area of the city.
The Nagasaki bombing occurred on the same date that the Soviet Union declared war on Japan and invaded Japanese-held territory in northeast Asia. Japan's leadership debated surrender before Emperor Hirohito announced acceptance of the Potsdam Declaration on August 15.