Operation Coronet was the planned second phase of Operation Downfall, aimed at Japan’s Kantō Plain.
Coronet was intended to follow Operation Olympic, the proposed invasion of southern Kyushu. Its objective was the Kantō Plain on Honshu, the main Japanese island and the region containing Tokyo. The plan envisioned landings near the capital followed by a drive inland and northward.
The operation was tentatively scheduled for March 1, 1946, after Olympic’s projected November 1945 landing. Planning assigned very large American forces, with the possibility of British Commonwealth reinforcements. Coronet was expected to be even larger than Olympic because of the strategic importance and population of the Tokyo region.
Japan’s surrender made both operations unnecessary. Coronet therefore belongs to the history of planned operations rather than completed campaigns. Its existence is also why discussions of Japan’s surrender often include counterfactual questions about a possible invasion, although the invasion’s actual casualty totals can never be known.