By 1939, the Imperial Japanese Navy (IJN) had developed the Kantai Kessen (Decisive Battle Doctrine), an offensive/defensive doctrine in support of planned offensives to seize the vital tin, rubber, and oil resources of Malaya and the Dutch East Indies.
As it was assumed that these attacks would bring the United States into the war in support of Britain and the Netherlands, the Philippines were also targeted in order to eliminate the US Asiatic Fleet and the American air bases, which could threaten the primary Japanese offensives.
The Japanese anticipated that the US Pacific Fleet would sortie from its West Coast bases to relieve the beleaguered American garrison of the Philippines. IJN submarines would make the initial attacks before being joined by long-range bombers as the Americans came within range of Japanese air bases in the Marianas and Caroline Islands.
