What was the Allied plan to invade Japan’s home islands before its 1945 surrender?

Operation Downfall was the Allied plan to invade Japan’s home islands before its 1945 surrender.

The proposed operation was designed for a full-scale invasion of mainland Japan if the country did not surrender. It had two major stages: Operation Olympic, aimed at southern Kyushu in November 1945, and Operation Coronet, aimed at the Kanto Plain near Tokyo in spring 1946.

Operation Downfall was canceled after Japan accepted the Allied surrender terms. Its projected scale was enormous. If carried out, it would have been the largest amphibious operation in history, surpassing the Normandy landings. Allied planners expected fierce resistance, and casualty estimates varied widely.

Operation Downfall is often confused with Operation Olympic, but Olympic was only the first phase of Downfall. Japanese planners also prepared Operation Ketsugo, a defensive strategy for resisting an invasion. The surrender meant that none of these planned operations against the Japanese home islands took place.