Smoke over one city sent the second atomic bomb to Nagasaki instead

On 9 August 1945 the primary target for America's second atomic bomb was the arsenal city of Kokura. Haze and smoke — some drifting up from a firebombing raid on a nearby city the day before — hid the aiming point after three passes over the city. Running low on fuel, the crew diverted to the secondary target, Nagasaki, which briefly cleared enough to bomb visually.

— Richard Rhodes, The Making of the Atomic Bomb — 1986, on the Nagasaki mission
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