The Philippine route linked Japanese fuel and ammunition

Japan's Shogo plan treated defense of the Philippines as inseparable from survival of the Combined Fleet. Losing the archipelago would cut the remaining southern shipping route, leaving ships in Japan short of oil or ships in the south cut off from ammunition and other support. American submarines were already exploiting this vulnerable connection between the southern resource area and the home islands. By late 1944 Japan's air groups and light forces had declined, making its heavy surface ships the strongest remaining tool for trying to keep that route open. The resulting fleet commitment was therefore driven by logistics as much as by the immediate defense of the Leyte landing beaches.