The Battle of the Philippine Sea was an air-sea battle of the Pacific campaign fought between the U.S. Navy and the Imperial Japanese Navy on the 19th and 20th of June, 1944, off the Mariana Islands. The action was a disaster for the Japanese forces, who lost almost all of their carrier-borne aircraft and a third of the carriers involved in the battle. The aircraft carrier force of the IJN was no longer militarily effective.