What was the planned Allied invasion of Japan, canceled after its surrender, called?

The planned Allied invasion of Japan was called Operation Downfall.

Operation Downfall was the proposed invasion of the Japanese home islands if Japan continued fighting. It had two major stages: Operation Olympic, aimed at southern Kyushu, and Operation Coronet, aimed at the Tokyo Plain on Honshu. Olympic was scheduled for November 1945, with Coronet planned for March 1946.

The invasion was never carried out because Japan accepted the Allied terms and formally surrendered in September 1945. Planning documents anticipated enormous casualties on both sides, although estimates varied and historians continue to debate how likely the projected losses were.

Operation Downfall is sometimes confused with its component operations. Olympic and Coronet were parts of Downfall, not alternative names for the entire plan. The atomic bombings, the Soviet declaration of war against Japan, Japan’s internal political crisis, and the emperor’s decision all formed part of the final sequence leading to surrender.