It was by no means a unanimous decision and basically the argument had been shelved until preparations were completed in late fall 1945 and the bombs dropped in of course August.

Admiral King (CNO) and Nimitz (CINCPAC) were very much against the invasion and preferred blockade and bombard, and were equally dismayed that MacArthur would be in command. While Marshall (Army Chief of Staff) and MacArthur were constantly pushing for DOWNFALL and saw nothing but unnecessarily prolonging the war as the alternative.

In Spring 1945 the Navy essentially caved as it allowed planning to go forward and bide their time during the 6 months or so it would be until it was time to get serious. However by August 1945 intelligence had tracked a major increase of IJA formations either brought back from China by what remained of the merchant marine or brought from less key areas toward the invasion areas.

These reports led the Navy to confirm their belief that the invasion as being planned by MacArthur would be a blood bath and by no means guaranteed successful, and even Marshall began to have doubts, however MacArthur continued to believe his plan would work and planning continued into August, when of course the atomic bombs were dropped.

Had the war continued to October with no prospect of ending it is very likely another major debate would have occurred in the high command, and it was by then a toss up of if DOWNFALL would have occurred as we know it. In particular by presenting Truman with a non united front it is likely King would at least have fundamentally undermined Truman's trust in the plan and would have agreed to have it altered or scrubbed. Up to that point King and Marshall had hashed out their differences in sometimes extremely heated closed door "talks" and always presented a united front to either the British or elected leaders, breaking that would have shown how deeply King was opposed to the plan and he confirmed to Nimitz he was ready to do just that.