Kokura was the primary target of the Bockscar mission before it diverted to Nagasaki.
On August 9, 1945, Bockscar approached Kokura to deliver Fat Man. The target area was obscured by clouds and smoke, including smoke associated with fires from a bombing raid on nearby Yahata. After multiple attempts, the crew could not identify the aiming point visually.
Because fuel was running low, Major Charles W. Sweeney and weapons specialist Frederick Ashworth decided to proceed to the secondary target, Nagasaki. A brief opening in the clouds there permitted a visual drop.
Kokura’s role created the phrase “Kokura’s luck,” used to describe the way weather and smoke protected a place from the intended attack. The mission’s primary-target designation is distinct from the city that was ultimately bombed.