In WWII, What was Operation Downfall?

In WWII, the Allied plan for the invasion of the Japanese home islands was named Operation Downfall.

There were two parts to the plan: Operation Olympic and Operation Coronet. Scheduled to be launched in November 1945, Operation Olympic was intended to capture the southern third of the southernmost Japanese island, Kyushu, launching an attack from the recently captured island of Okinawa, an island to be used as a staging area.

In early 1946, Operation Coronet would be initiated- the planned invasion of the Kanto Plain, near Tokyo, on the main Japanese island of Honshu.

If Operation Downfall had taken place, it would have been the largest amphibious operation in history. It was canceled when Japan surrendered on August 15, 1945, following the atomic bombings of Hiroshima and Nagasaki.

U.S. military planners assumed that organized military forces of the Japanese Empire and the hostile civilian population, would result in significantly high Allied casualties. The estimated casualty figures varied considerable depending on the source but later became a crucial point of contention in the postwar debate over the atomic bombings of Hiroshima and Nagasaki.