What was the Allied code name for the proposed invasion of Japan’s home islands in 1945?

Operation Downfall was the Allied code name for the proposed invasion of Japan’s home islands in 1945.

The plan was created in case Japan did not surrender after the atomic bombings, the Soviet declaration of war, and continued Allied attacks. Downfall was divided into 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.

The proposed invasion would have required enormous forces and was expected to produce severe casualties on both sides. Japanese planners anticipated an invasion and prepared Operation Ketsugo, a strategy for defending the home islands with military units and civilian mobilization.

Downfall never took place. Japan accepted the Allied surrender terms in August 1945, so the invasion plans were canceled. It is sometimes confused with Olympic or Coronet, but those were components of Downfall rather than alternative names for the entire operation.