What codename did the Allies give their planned invasion of Japan in 1945?

The Allies gave their planned invasion of Japan the codename Operation Downfall.

Operation Downfall was the proposed Allied invasion of the Japanese home islands if Japan did not surrender. It consisted of two planned phases: Operation Olympic, aimed at southern Kyushu, and Operation Coronet, aimed at the Tokyo area of Honshu.

Olympic was scheduled for November 1945, while Coronet was planned for March 1946. Allied planners expected the operation to require enormous forces and anticipated fierce resistance from Japan’s military and civilian population. Preparations included troop movements, landing plans, logistics, and estimates of potential casualties.

The invasion never occurred. Japan accepted the Allied terms in August 1945 after the atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war, and internal Japanese deliberations. Operation Downfall is therefore often discussed as the invasion that was planned but made unnecessary by Japan’s surrender. Operation Olympic was one component of Downfall, not the name of the entire plan.