I was told the the Army had half a million body bags on hand for the invasion of the home island. Don't know that for a fact but I did see about 100,000 in storage 30 plus years later and that was after Korea and Vietnam used up too large a number. Any invasion of the home islands would have ended with the loss of not only our own men but perhaps five million or more civilian and military personnel. Fortunately we did not have to find out.
On a personal note my father had been island hopping across the Pacific and would have been going into Japan if his last wound healed enough to return him to duty and they would have by September at the latest he figured. If they figured we'd loose half a million troops what would have been the Japanese losses between military and civilian? Five to ten million. The complete loss of every male from age 12 to 60? In my mind the two bombs, which killed 200,000 plus, saved millions. Thank God for men with the courage to do what must be done to see that we did not waste more good men in a war which was won. Damn the bleeding hearts who weren't there and never would have been at risk in an war.