As the war situation deteriorated for the Japanese and the territories controlled by the "Area Fleets" fell one after another to the United States Navy, the Imperial General Headquarters and the Imperial Japanese Navy General Staff acted to force the American fleet into a "decisive battle" in the Philippines per the "kantai kessen" philosophy. In the resultant Battle of the Philippine Sea and the Battle of Leyte Gulf the Japanese fleet was severely depleted. The remnants of the Combined Fleet fled to Okinawa, but further operations were hindered by lack of fuel and air cover. By the time of the final suicide mission of the battleship "Yamato" in Operation Ten-Go, the Combined Fleet had ceased to exist as an effective combat force.