I have read that the sea blockade (oil etc) was so effective that Japan's war machine had only a month or so left before it became ineffective. This together with the non-stop conventional bombing going on at the time, does ask the question if an invasion would have been necessary. Just anther view because I cannot envisage a country without oil causing hundreds of thousands of casualties to any invading force.
I can’t help feeling that the decision to drop the bomb was more a political one than a military one.
However the decision was made and the Colonel did his duty and can on no account, take any blame for the aftermath of that decision.