Did America know how much damage the atomic bombs would cause before they dropped them?
Yes, America knew very well what the effects of the bomb were. Atomic bombs were tested before release, and while the effects of radiation were not entirely clear, it was certainly known that large amounts of radioactive fallout would ensue. The thing was, at the time, the dropping of the bomb was not as controversial an issue as it is seen to be today. Truman was getting word of thousands of Allied deaths per day, with estimates of up to a million dead with a land invasion of Japan. The cost of some Japanese lives (albeit civilian, although one must recall the Japanese were taught to be totally committed to the emperor and the war) seemed to be less significant in comparison. Also, I personally think Japan would have been insane not to surrender. A third bomb probably wouldn’t be necessary so much as the threat of one once they had seen what a nuke could do.
