The Western Sea Frontier, headquartered in San Francisco, California, USA, was responsible for the sea defense of the Pacific coast of the United States and Mexico during World War II. The Western Sea Frontier was composed of many forces and commands, including the Eleventh, Twelfth, and Thirteenth Naval Districts. The Western Sea Frontier consisted of the Pacific Coastal regions lying west of the Cascade and Sierra Nevada Mountains as well as of Alaska.
Western Sea Frontier was designated in official U.S. Navy records:
Admiral Earnest J. King, First Report to the Secretary of the Navy: Covering our Peacetime Navy and our Wartime Navy and including combat operations up to 1 March 1944. April 1944, pp. 75-88.
Samuel Eliot Morrison, History of United States Naval Operations in World War II, The Battle of the Atlantic, 1939-1943. ISBN 0-7858-1302-0