When was Operation Coronet, the planned invasion of Honshu, scheduled to begin?

Operation Coronet, the planned invasion of Honshu, was scheduled to begin on March 1, 1946.

Coronet was the second phase of Operation Downfall, the proposed Allied invasion of Japan. It was intended to land forces on the Kanto Plain near Tokyo after Operation Olympic’s planned invasion of southern Kyushu. The operation would have been one of the largest amphibious campaigns ever contemplated.

Planning documents called the planned start date “Y-Day.” Coronet was never launched because Japan accepted the Potsdam Declaration in August 1945 and formally signed its surrender on September 2. The operation therefore remains a counterfactual military plan rather than a battle.

A common mix-up is assigning Coronet the date November 1, 1945. That was the scheduled date for Olympic, the Kyushu phase. Coronet’s projected date was later, March 1, 1946, and its target was Honshu rather than Kyushu.