Operation Coronet was the planned Operation Downfall invasion of Honshu near Tokyo.
Coronet was designed as the second stage of the proposed Allied invasion of Japan. It would have targeted the Kantō Plain on Honshu, the main Japanese island and the location of Tokyo. The tentative start date was March 1, 1946, after the planned invasion of southern Kyushu.
The first stage, Operation Olympic, was scheduled for November 1, 1945, and aimed to seize southern Kyushu. Airfields and bases captured there would have supported the later advance toward Honshu. Coronet was expected to be even larger than Olympic and would have involved forces from the U.S. First and Eighth Armies.
Japan’s surrender canceled both operations. The plans are often mixed up because Operation Downfall was the overall invasion plan, while Olympic and Coronet were its two component operations. Neither Olympic nor Coronet was executed.