Kokura was the primary target of the 9 August 1945 atomic-bomb mission that instead struck Nagasaki.
The B-29 bomber Bockscar carried the plutonium weapon Fat Man from Tinian. Its mission plan listed Kokura as the primary target and Nagasaki as the secondary target. When the aircraft reached Kokura, clouds and smoke obscured the aiming point, preventing the required visual bombing approach.
After several attempts and worsening fuel limitations, the crew turned toward Nagasaki. A break in the clouds allowed a visual approach, and Fat Man detonated over the city’s Urakami Valley. The mission therefore connected Kokura and Nagasaki in a way often simplified in popular accounts: Nagasaki was the bombed city, but Kokura was the original primary target.
The attack occurred three days after the bombing of Hiroshima and during the final crisis that preceded Japan’s surrender. The mission is also remembered through the phrase “Kokura’s luck,” although the actual conditions involved clouds, smoke, fuel, and targeting rules.