What was the proposed Allied invasion of Japan called in World War II?

The proposed Allied invasion of Japan was called Operation Downfall.

Downfall was the overall plan for invading the Japanese home islands if Japan did not surrender. It had two major stages: Operation Olympic, aimed at southern Kyushu, and Operation Coronet, aimed at the Kanto Plain near Tokyo. Olympic was planned for November 1945, with Coronet planned for 1946.

The plan was never executed because Japan surrendered in August 1945. Allied planners expected a difficult campaign, and the Japanese military prepared its own defense plan, known as Operation Ketsugō. The proposed invasion would have required enormous naval, air, and ground forces and could have produced very heavy casualties.

Operation Downfall is often confused with Olympic or Coronet. Downfall was the umbrella operation; Olympic and Coronet were its component invasions. The plan also differed from Operation Downfall's later popular use in debates about casualty estimates, because contemporary estimates varied considerably and no invasion battle occurred to establish an actual toll.