Kokura was the primary target before the 1945 atomic bombing mission diverted to Nagasaki.
On August 9, 1945, B-29 Bockscar carried the Fat Man atomic bomb toward Kokura. The city contained a major arsenal and was selected as the primary target. However, clouds and smoke obscured the aiming point, making the visual bombing approach required by mission orders impossible.
The crew made several attempts to find a clear view and consumed valuable fuel in the process. Kokura was also affected by smoke from a large conventional bombing raid on nearby Yahata the previous day. After the repeated attempts, the aircraft turned toward Nagasaki, the secondary target.
Nagasaki was itself partly obscured by clouds, but a last-minute opening permitted a visual approach. Fat Man was dropped over the city’s industrial valley. The episode produced the expression “Kokura’s luck,” later used to describe narrowly escaping a catastrophe, although the phrase is a retrospective popular expression rather than an official wartime term.