What was the name of the Allied plan for a full-scale invasion of Japan if it did not surrender in 1945?

Operation Downfall was the Allied plan for a full-scale invasion of Japan in 1945.

The plan had two major stages. Operation Olympic called for an invasion of Kyushu, Japan’s southernmost main island, while Operation Coronet envisioned a later assault on Honshu near Tokyo. Olympic was scheduled for November 1945, with Coronet planned for March 1946.

The invasion was never carried out because Japan surrendered in August 1945. The atomic bombings of Hiroshima and Nagasaki, the Soviet entry into the war against Japan, and the internal Japanese decision to accept the Allied terms ended the need for the planned campaign.

Operation Downfall is sometimes mistakenly used as the name of one invasion landing. Downfall was the overall operation; Olympic and Coronet were its two principal components. The planned casualties remain debated because they depend on assumptions about Japanese resistance, Allied tactics, and the eventual size of the invasion force.