Operation Ketsugō was Japan’s military plan for defending the home islands against an Allied invasion.
Japanese leaders expected the Allies to attack Kyushu first and organized Ketsugō as an all-out defense strategy. The plan called for concentrating troops, aircraft, naval craft, and civilian defenders around likely landing areas rather than preserving forces for a conventional retreat.
Ketsugō was designed to inflict such heavy losses that Japan might obtain better surrender terms or discourage an invasion. Japanese planners recognized the likely targets of the proposed Allied Operation Olympic and attempted to move reinforcements toward southern Kyushu.
The plan was never tested in combat because Japan surrendered before Downfall began. Its existence is sometimes confused with Downfall, but Downfall was the Allied invasion plan, while Ketsugō was Japan’s defensive response to that anticipated invasion.