What was the name of the proposed Allied invasion plan for Japan’s home islands in late 1945 and 1946?

Operation Downfall was the proposed Allied invasion plan for Japan’s home islands in late 1945 and 1946.

The plan had two major stages. Operation Olympic was scheduled for November 1945 and would have attacked southern Kyūshū. Operation Coronet was planned for spring 1946 and would have targeted the Kantō Plain near Tokyo on Honshu.

Downfall was canceled after Japan surrendered. Allied planners expected an enormous amphibious campaign, and casualty estimates varied widely. If carried out, it would have involved one of the largest concentrations of military forces ever assembled and would likely have surpassed the Normandy landings in scale.

Japan prepared its own defense plan, Operation Ketsugō, anticipating an Allied invasion. The atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war, and the Soviet invasion of Manchuria changed the strategic situation before Downfall could begin. The surrender made the invasion unnecessary.