War Plan Orange (commonly known as Plan Orange or just Orange) was invoked. Predating the Rainbow plans, which presumed allies, Orange was predicated on the U.S. fighting Japan alone. It anticipated a withholding of supplies from the Philippines and other U.S. outposts in the Western Pacific (they were expected to hold out on their own), while the Pacific Fleet marshaled its strength at bases in California, and guarded against attacks on the Panama Canal.
After mobilization (the ships maintained only half of their crews in peacetime), the fleet sailed to the Western Pacific to relieve American forces in Guam and the Philippines. Afterwards, the fleet sailed due north for a decisive battle against the Imperial Japanese Navy, and then blockade the Japanese home islands.
The Imperial Japanese Navy developed a counter-plan to allow the Pacific Fleet to sail across the Pacific while using submarines and carrier attacks to weaken it. The Japanese fleet attempt to force a battle against the U.S. in a 'decisive battle area', near Japan, after inflicting such attrition. This is in keeping with the theory of Alfred Thayer Mahan, a doctrine to which every major navy subscribed before World War II, in which wars would be decided by engagements between opposing surface fleets (as they had been for over 300 years). It was the basis for Japan's demand for a 70% ratio (10:10:7) at the Washington Naval Conference, which would give Japan superiority in the 'decisive battle area', and the U.S.'s insistence on a 60% ratio, as 70% superiority was believed to be necessary for a successful attack.
Disasterously the American war planners failed to appreciate that technological advances in submarines and naval aviation had made Mahan's doctrine obsolete. In particular, the American planners did not understand that aircraft could sink battleships, nor that Japan might put the U.S. battleship force (the Battle Line) out of action at a stroke.
American plans changed after the failure of War Plan Orange. Even after major Japanese defeats like Midway, the U.S. fleet favored a methodical 'island-hopping' advance, never going far beyond land-based air cover.
Moreover, by their obsession with 'decisive battle', the Imperial Japanese Navy would ignore the vital role of antisubmarine warfare. Germany and the U.S. would demonstrate the need for this with their submarine campaigns against Allied and Japanese merchant shipping respectively. The American campaign ultimately choked Japan's industrial production. Japan also notably failed to institute an anti-commerce campaign themselves.