Kokura was the primary target before the Nagasaki bombing mission diverted to another city.
On August 9, 1945, the B-29 Bockscar approached Kokura carrying the atomic bomb Fat Man. The city contained the Kokura Arsenal, an important military-industrial complex, and had been selected as the mission's primary target.
Cloud cover and smoke obscured Kokura. The crew made several attempts to locate a suitable visual aiming point, but the mission orders required visual bombing rather than relying only on radar. With fuel running low, the aircraft turned toward Nagasaki, the secondary target.
A temporary break in the clouds over Nagasaki allowed the crew to release Fat Man. The event gave rise to the expression “Kokura's luck,” describing how weather and smoke spared the city from the atomic attack. The mission illustrates that target lists and intended targets were not always the same as the cities ultimately bombed. Japan announced its surrender six days later, on August 15.