What was the codename of the planned Allied invasion of Japan that never took place in 1945?

Operation Downfall was the planned Allied invasion of Japan that never took place in 1945.

The plan was divided into two major stages. Operation Olympic would have invaded southern Kyūshū in November 1945, while Operation Coronet would have targeted the Kantō Plain near Tokyo in March 1946. Together, these operations were known as Operation Downfall.

Allied planners expected the invasion to be extremely costly. They studied Japanese defensive preparations, geography, weather, and the likely mobilization of soldiers and civilians. The projected casualties were uncertain and remain a subject of historical debate.

Japan’s surrender after the atomic bombings, the Soviet entry into the war, and internal Japanese deliberations made the invasion unnecessary. Operation Downfall was therefore canceled before Allied troops landed on the Japanese home islands.