What was the codename for the planned Allied invasion of Japan’s home islands?

Operation Downfall was the codename for the planned Allied invasion of Japan’s home islands.

The plan had two major stages. Operation Olympic was intended to invade southern Kyushu in November 1945, while Operation Coronet was planned for the Kanto Plain near Tokyo in spring 1946. Japan’s surrender made both operations unnecessary, so Downfall was canceled.

The invasion plans reflected Allied expectations that Japan might continue fighting after the atomic bombings and the Soviet entry into the war. Military planners prepared for extremely costly combat and organized large forces, ships, aircraft, and supply systems for a possible assault.

Operation Downfall is often confused with Operation Olympic or Operation Coronet. Downfall was the overall plan; Olympic and Coronet were its two component operations. Operation Overlord, by contrast, was the Allied invasion of Normandy in June 1944.