What was the proposed Allied invasion plan for Japan's home islands called?

The proposed Allied invasion plan for Japan's home islands was called Operation Downfall.

Downfall was a two-part plan. Operation Olympic was scheduled to invade southern Kyushu in November 1945, while Operation Coronet was planned for the Kanto Plain near Tokyo in spring 1946. The invasion was canceled after Japan surrendered.

The plan reflected Allied expectations that Japan might continue fighting despite the bombing of Hiroshima and the changing strategic situation. Planners prepared for an extremely large operation involving naval forces, air support, and numerous ground divisions. The intended invasion would have been larger than the Normandy landings.

Operation Downfall is sometimes confused with its two component operations. Olympic and Coronet were not alternative names for the whole plan; they were the first and second stages within it. The actual surrender made both unnecessary, so Downfall remained a plan rather than a battle.