What name was given to the planned Allied invasion of Japan’s main island, Honshu, in 1946?

Operation Coronet was the planned Allied invasion of Honshu in 1946.

Coronet formed the second stage of Operation Downfall, the proposed invasion of Japan’s home islands. Planners intended to land on the Kantō Plain near Tokyo on March 1, 1946, after the first phase, Operation Olympic, had invaded Kyushu in November 1945.

The target area was strategically important because it contained Tokyo, Japan’s political center, as well as major transport routes and industrial facilities. Allied planners anticipated that Japanese forces and civilians might resist the invasion fiercely. Preparations therefore included the projected use of very large numbers of troops, landing craft, aircraft, and naval vessels.

Japan’s surrender in August 1945 made Coronet unnecessary. The operation is sometimes mistakenly identified as the whole invasion plan; Downfall was the umbrella name, while Coronet specifically referred to the Honshu phase. Sea Lion was a separate German plan to invade Britain in 1940.