With the crippling of the American fleet at Pearl Harbor. the Philippines was cut off from any real assistance from the United States. On December 22. 1941. the Japanese launched their attack on Lingayen Gulf. and American and Filipino forces began their famous rearguard action on Bataan. The retreat down the peninsula led to the fortress island of Corregidor. which stands at the entrance of Manila Bay. At great cost. Corregidor was held until May 6. 1942. after having resisted longer than any area conquered by Japan in its southeast Asiatic sweep. Throughout the Japanese occupation. Filipinos waged devastating guerrilla warfare.