When MacArthur returned to the Philippines, the United States Navy prepared for the largest naval battle in history – the Battle of Leyte Gulf. On October 20, 1944, United States troops invaded the island of Leyte as part of a strategy aimed to isolate Japan from the countries it had occupied in Southeast Asia, while also depriving Japanese forces and industry of vital oil supplies. Though weakened, the Imperial Japanese Navy mobilized nearly all of its remaining major naval vessels in an attempt to defeat the Allied invasion but was repulsed by the U.S. Navy's Third and Seventh Fleets. The IJN failed to achieve its objective, suffered heavy losses, and never sailed to battle in comparable force thereafter.