What was the overall Allied plan to invade Japan’s home islands if Japan did not surrender in 1945?

Operation Downfall was the overall Allied plan to invade Japan’s home islands if Japan did not surrender in 1945.

The proposed operation had two major phases. Operation Olympic was intended to land on Kyūshū, Japan’s southernmost main island, in November 1945. Operation Coronet was planned for spring 1946 and would have targeted the Kantō Plain near Tokyo on Honshū.

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 Japanese-held Manchuria. The cancellation prevented what planners expected to be an enormous amphibious campaign against a heavily defended homeland.

Operation Downfall is often confused with Olympic or Coronet, but those were component operations within the larger plan. It is also distinct from Japan’s defensive Operation Ketsugō, which was designed to resist the expected Allied landings. Because the invasion never happened, casualty estimates remain projections rather than recorded battlefield totals.