Operation Coronet was the planned second phase of the Allied invasion of Japan aimed at the Tokyo region. It formed the second half of Operation Downfall, following the proposed invasion of Kyushu known as Operation Olympic.
Coronet was tentatively scheduled for March 1, 1946, under the code name Y-Day. The plan called for landings on the Kanto Plain, including areas near Kujukuri Beach and Sagami Bay, followed by an advance toward Tokyo. The operation was expected to be larger than Olympic.
Up to 45 American divisions could have been assigned to the initial landing and follow-up operations, with additional British Commonwealth forces potentially joining later. Allied commanders expected the Japanese defense of the home islands to be extensive and costly.
Japan’s surrender in August 1945 prevented Coronet from being launched. The code names are easy to mix up: Olympic referred to Kyushu, Coronet referred to the Tokyo-area invasion, and Downfall referred to the complete two-part invasion plan.