Operation Coronet was planned to invade Japan's Kantō Plain during the proposed 1946 invasion.
Coronet was the second phase of Operation Downfall, the Allied plan for invading Japan's home islands. Planners intended to land on the Kantō Plain, the broad lowland surrounding Tokyo and Yokohama on Honshu. The operation was scheduled for spring 1946.
The first phase, Operation Olympic, was aimed at southern Kyushu and was scheduled for November 1945. Captured airfields there would have helped support the later assault on Honshu. Japan's surrender made both operations unnecessary, so Coronet never moved beyond planning.
The Kantō Plain was strategically important because it contained Tokyo, major transport links, industrial facilities, and a large share of Japan's population. Its geography also offered room for a massive amphibious landing, although Japanese planners expected the area to become the center of fierce resistance.