Why were Herosima and Nagasaki chosen?

Answer 1

As the war in Europe was ending the bombs were not quite ready yet. It had been the plan to use the bomb against Germany but the surrender of Germany on May 8 came before the device was operational. The first test explosion came on July 16. Meanwhile, General Leslie Groves, head of the Manhattan Project that made the bombs, had formed a targeting committee, which met in April and May 1945 to decide which cities in Japan would be targets. There were several criteria. The committee wanted a city large enough that the blast could not completely destroy it, so as to get an accurate idea of the radius of devastation that actually could be achieved. Also for this reason they did not want a city that had already sustained heavy damage from conventional bombing, so all damage could be known to have been caused by the atomic bomb. The US 20th Air Force had been bombing Japanese cities from its bases in the Mariana Islands, since those Islands were captured in the summer of 1944. After some experimentation fire bombing had been found to be very effective against Japanese cities, and many of the larger ones already had a burned out city center. There were 18 cities on the list of the targeting committee. The five best prospects, in terms of size and unbombed status, were Kyoto, Hiroshima, Kokura, Niigata, and Yokohama. US Secretary of War Henry Stimson removed Kyoto from consideration, as he had been in that city on his honeymoon, and understood its cultural significance. Ultimately Hiroshima was selected as the first target as much because a unique, T-shaped bridge, the Aoki Bridge, provided an excellent and easily identifiable aiming point for the bombardier. Three days later the intended target was the city of Kokura, but the weather plane that flew over ahead of the nuclear bomber radioed back word that Kokura was covered over by clouds, which spared that city, and so the backup target of Nagasaki received the attack.