Kokura was the primary target of the atomic bombing mission that ultimately struck Nagasaki.
On August 9, 1945, the B-29 Bockscar carried the plutonium bomb Fat Man toward Kokura Arsenal, a major Japanese military facility. Smoke and cloud cover obscured the target, and the crew could not obtain the visual conditions required for the planned bombing. After several attempts, the aircraft proceeded to its secondary target, Nagasaki.
Nagasaki also had important industrial and military facilities, including shipyards and armaments production. The bomb detonated there at approximately 11:02 a.m. local time. The city's surrounding hills affected the blast pattern, but destruction and casualties were still severe.
Kokura's role is frequently omitted from simplified accounts that mention only Hiroshima and Nagasaki. The mission's target sequence explains why Nagasaki was not the original destination for the second atomic bomb. The same day, the Soviet Union was also launching its invasion of Japanese-held Manchuria, adding another major pressure on Japan's leadership.