What was the codename for the first phase of the planned invasion of Japan?

Operation Olympic was the first phase of the planned Allied invasion of Japan.

Olympic was intended to begin in November 1945 with landings on Kyushu, Japan’s southernmost main island. The objective was to seize the southern part of the island and establish airfields and other positions for follow-on operations.

Olympic formed the opening stage of the larger Operation Downfall plan. The second stage, Operation Coronet, was intended to invade the Kantō Plain near Tokyo on Honshu in spring 1946. Allied forces had already captured Okinawa, which planners expected to use as a staging area for the Kyushu campaign.

The plan was never executed because Japan surrendered in August 1945 and signed the formal instrument in September. Operation Olympic is therefore a planned operation, not the name of an actual battle. A common mix-up is reversing Olympic and Coronet: Olympic concerned Kyushu first, while Coronet concerned the Tokyo region later.