What was the planned Allied invasion of Japan’s main island Honshu called under Operation Downfall?

The planned Allied invasion of Japan’s main island Honshu was called Operation Coronet.

Coronet was the second phase of Operation Downfall, the proposed invasion of the Japanese home islands. It was intended to follow Operation Olympic, which would have landed Allied forces on Kyushu. Coronet would then have attacked the Kantō Plain near Tokyo, Japan’s political and industrial center.

Planners tentatively scheduled the operation to begin on March 1, 1946, designated “Y-Day.” The plan called for a very large force, including American armies landing at Kujūkuri Beach and Hiratsuka. Reinforcements would have followed as Allied forces advanced toward Tokyo and inland areas.

Coronet was never carried out. Japan’s surrender in August 1945 eliminated the need for an invasion, while the formal surrender ceremony followed on September 2. Operation Olympic and Operation Coronet are often confused because both belonged to Operation Downfall, but Olympic concerned Kyushu and Coronet concerned Honshu.