What was the planned Allied invasion of southern Kyūshū called after Japan’s surrender canceled it?

The planned Allied invasion of southern Kyūshū was called Operation Olympic.

Olympic was the first stage of Operation Downfall, the proposed Allied invasion of Japan’s home islands. It was scheduled for November 1945 and was intended to seize the southern part of Kyūshū, Japan’s southernmost main island. The captured territory would have provided airfields and staging areas for later operations.

Japan’s surrender in August 1945 made Olympic unnecessary, so the operation was canceled before it began. The plan had required a huge concentration of troops, ships, aircraft, and supporting forces, and planners expected fierce resistance from Japanese military units and civilians.

Operation Olympic is often confused with Operation Coronet, the planned second stage of Downfall. Coronet was aimed at the Kantō Plain near Tokyo and was tentatively scheduled for spring 1946. Downfall was the overall invasion plan; Olympic and Coronet were its two component operations.