Operation Coronet was the second part of Operation Downfall - the planned invasion of Japan. Coronet was planned as a massive amphibious landing on beaches near to Tokyo. Vital air cover from bases in Kyushu, taken in Operation Olympic, would greatly assist the landings, according to the planning.
Operation Coronet was the second part of the whole plan to invade Japan. Beaches to the south of Tokyo were deemed capable of supporting a massive landing and the actual invasion was scheduled to start on December 1st, 1945, though this was later postponed to march 1946. In theory, the force that would have invaded the beaches of Kanto would have included men who had fought in the European theatre of war and in other areas of South-East Asia. Therefore, it would not have been an exclusively American force. On paper, Britain would have provided in the region of twelve aircraft carriers and a number of battleships. The incoming troop ships would have received air cover from planes based in Kyushu, conquered in Operation Olympic, and Coronet had built into it the taking of Tokyo. The fanaticism with which the Japanese were likely to defend the city that their emperor lived in, would have caused massive casualties for the Americans and her allies, even with air cover. The fear of what would de-generate into guerilla warfare within a city like Tokyo - even though it had been seriously destroyed by fire bombing - was one of the reasons why President Truman authorised the use of atomic bombs on both Hiroshima and Nagasaki in August 1945. The surrender of Japan on September 2nd, meant that neither Olympic or Coronet were carried out.