What was the planned Allied invasion of the Kanto Plain near Tokyo called?

The planned Allied invasion of the Kanto Plain near Tokyo was called Operation Coronet.

Coronet was the second stage of Operation Downfall, the proposed invasion of Japan. It was planned for spring 1946 and would have targeted the Kanto Plain on Honshu, Japan’s largest island, where Tokyo is located.

The operation was intended to follow Operation Olympic, which would have seized southern Kyushu in November 1945. Allied planners expected bases on Kyushu to support the larger assault toward Tokyo. Coronet would have required enormous land, sea, and air forces.

Japan surrendered before either operation began. Coronet is sometimes mistaken for Downfall, but Downfall was the overall invasion plan, while Coronet was its planned Honshu phase.