> On 3 July, the Joint Chiefs of Staff placed (Hiroshima) off limits to bombers, along with Kokura, Niigata and Kyoto
Nagasaki was not explicitly saved, but was just a difficult target to hit:
> Nagasaki had been spared from firebombing because its geography made it difficult to locate at night with AN/APQ-13 radar.
> Unlike the other target cities, Nagasaki had not been placed off limits to bombers by the Joint Chiefs of Staff's 3 July directive, and was bombed on a small scale five times.
Anyone with better sources could please fill out the Wikipedia article some more:
https://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_a...
https://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_a...