The proposed Allied invasion plan called Operation Downfall had two phases.
The first phase, Operation Olympic, was planned for November 1945 and would invade southern Kyushu. The second, Operation Coronet, was planned for spring 1946 and would attack the Kanto Plain near Tokyo on Honshu.
Okinawa was intended to serve as a staging area for Olympic, while airfields captured in Kyushu would support the later advance toward Tokyo. Allied planners expected the operation to be enormous, with projected forces numbering in the hundreds of thousands for Olympic and more than one million personnel for Coronet.
Operation Downfall was never carried out. Japan accepted the Potsdam Declaration in August 1945, following the atomic bombings of Hiroshima and Nagasaki and the Soviet entry into the war against Japan. The cancellation spared both sides the expected casualties of a full-scale invasion, though estimates varied widely and remain debated.