Well, I don't know about the supply lines question (it strikes me as a very stretched premise on the face of it). But I would just point out this entire discussion is premised on the idea that Hiroshima and Nagasaki were targeted because of their ties to supply lines, and that there were no alternatives to targeting the supply lines than destroying the entire cities. This is totally incorrect. They were targeted because they were cities, and the goal of the atomic bombs was to terrify the Japanese into surrendering. One can agree or disagree with those motivations. But the documentation is very, very clear on this point. It was not a case of "oh, we have to target cities to achieve these tactical military aims." They were very deliberate about wanting to showcase the power of the atomic bombs in the most potent way they could, and they concluded that wiping cities off of the map was the best way to do that. So this is an entirely moot discussion.