Nagasaki was targeted by the atomic bomb nicknamed “Fat Man” before Japan surrendered.
The United States dropped Fat Man on Nagasaki on August 9, 1945. It was a plutonium-based implosion weapon carried by the B-29 bomber Bockscar. The bomb exploded over the city after the crew diverted from its primary target because of cloud cover and limited visibility.
Fat Man was the second atomic bomb used in warfare. The first, Little Boy, had been dropped on Hiroshima three days earlier, on August 6. Japan's leadership also faced the Soviet Union's declaration of war and invasion of Japanese-held Manchuria on August 9.
These events contributed to the decision to accept the Potsdam Declaration. Emperor Hirohito's recorded announcement was broadcast on August 15, while the formal surrender signing took place on September 2.