Operation Downfall was to be a strictly American operation. It called for using the entire Marine Corps, the entire Pacific Navy, elements of the 7th Army Air Force, the 8 Air Force 10th Air Force and the American Far Eastern Air Force. More than 1.5 million combat soldiers, with 3 million more in support or more than 40% of all servicemen still in uniform in 1945 - would be directly involved in the two amphibious assaults. Casualties were expected to be extremely heavy.????
source:kilroywashere dot org..
How many Allied soldiers will be involved in the invasion of Japan?
3 answers
So, from that source, how many U.S. troops would have been involved? Your source is accurate. Luckily, we never had to invade Japan. They surrendered first.
Even without an invasion or nuclear bombs Japan was all done. Between the American submarine fleet and surface/air fleets, they were being strangled. Japan does not have oil or many other vital supplies. Without merchant ships to and from Southeast Asia and elsewhere, they could not live. It would have been a terrible sacrifice of American troops to invade.