What was the code name for the planned 1946 Allied invasion of the Tokyo Plain?

The code name for the planned 1946 Allied invasion of the Tokyo Plain was Operation Coronet.

Coronet was the second stage of Operation Downfall, the proposed invasion of Japan. It was intended to follow Operation Olympic, which would have captured southern Kyushu in November 1945. Coronet was planned for spring 1946 and would have struck the Kantō Plain on Honshu, the main Japanese island.

The Kantō Plain contained Tokyo and was the political and industrial heartland of Japan. Allied planners expected Coronet to be larger than Olympic, with forces landing near Sagami Bay and the Bōsō Peninsula before advancing toward Tokyo. The planned date was known as Y-Day and was tentatively set for March 1, 1946.

Coronet never began. Japan surrendered before the invasion timetable could be reached. The name is therefore linked to the contingency planning of the final months of World War II, not to an actual Allied campaign. Operation Pastel, meanwhile, was a proposed deception plan connected with Olympic.