What was the planned Allied invasion of Japan's home islands called in World War II?

The planned Allied invasion of Japan's home islands in World War II was called Operation Downfall.

Downfall was a proposed two-stage invasion plan. Operation Olympic would have attacked southern Kyushu in November 1945, while Operation Coronet would have targeted the Kanto Plain near Tokyo in spring 1946.

The plan was canceled after Japan accepted the Allied surrender terms. The atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war, and the invasion of Manchuria all shaped the final decision to end the war before Downfall began.

Operation Downfall is sometimes mistaken for Olympic or Coronet. Those were component operations, while Downfall was the overall invasion plan. It would have required an enormous force and was expected to become the largest amphibious operation in history if carried out.