What was the planned Allied invasion of Japan called before Japan surrendered in 1945?

The planned Allied invasion of Japan before its 1945 surrender was called Operation Downfall.

Operation Downfall was the proposed invasion of Japan’s home islands. It was divided into Operation Olympic, aimed at southern Kyushu, and Operation Coronet, planned for the Kanto Plain near Tokyo. Olympic was scheduled for November 1945, with Coronet intended for 1946.

The plan was canceled after Japan surrendered following the atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war, and the Soviet invasion of Manchuria. Therefore, Downfall was never executed.

Operation Downfall is often confused with Olympic or Coronet. Those were component operations, not the name of the overall invasion plan. Had it occurred, Downfall would have involved an enormous Allied force and was expected to produce severe casualties on both sides.