What was the overall Allied plan for a ground invasion of Japan if surrender had not occurred?

Operation Downfall was the overall Allied plan for a ground invasion of Japan if surrender had not occurred.

The proposed operation had two major stages. Operation Olympic was planned for the invasion of southern Kyushu in November 1945. Operation Coronet was intended to follow with an invasion of the Kanto Plain near Tokyo in March 1946. Together, these operations formed the broader plan called Downfall.

Downfall was never carried out. Japan surrendered after the atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war, and the Soviet invasion of Manchuria. The planned invasion therefore remains a counterfactual military operation rather than a battle that took place.

Operation Downfall is often confused with Operation Overlord, the Allied invasion of Normandy in 1944. Overlord concerned Europe; Downfall concerned the Japanese home islands. Its projected scale reflected the Allies’ expectation of fierce resistance and very high casualties.