Sea Frontier

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Sea Frontiers were several, now disestablished, commands of the United States Navy as areas of defense against enemy vessels, especially submarines, along the U.S. coasts. They existed from 1 July 1941 until in some cases the 1970s. Sea Frontiers generally started at the shore of the United States and extended outwards into the sea for a nominal distance of two hundred miles.

As early as 1927 the Navy's plans for the coastal defense of the United States and its Territories and possessions provided for the establishment of Naval Coastal Frontiers that would be larger operational commands than the individual Naval Districts.^[1] On 1 July 1941, the Chief of Naval Operations formally established several Naval Coastal Frontiers; on 6 February 1942, these were renamed Sea Frontiers. Each Frontier was a geographic area, usually comprising a number of Naval Districts but including in addition the outer shipping lanes in its sea area. The land areas of the Frontiers corresponded roughly to the Army's Defense Commands, but the boundaries were not identical. The Frontier Commander was usually also the commandant of a Naval District within the Frontier. The chief responsibilities of the Sea Frontiers during World War II were operational; Frontier forces engaged actively in scouting for enemy forces, particularly submarines, and in attack on any enemy units within their boundaries. Toward the end of the war the Frontiers were assigned administrative and logistic functions in addition to their operational responsibilities.

Navy General Order No. 143, issued on 3 February 1941, stated that Commandants of United States naval districts and Commanders of Naval Coastal Frontiers have administrative responsibility direct to the Navy Department for local and coastal forces; but Commanders of Naval Coastal Frontiers have task responsibility to the Chief of Naval Operations for Naval Coastal Frontier Forces.^[2]

In addition to U.S. Navy Sea Frontiers, the Canadian Northwest Atlantic was the responsibility of the Royal Canadian Navy. This formation was very active since the majority of trans-Atlantic convoys originated or terminated in Canadian waters.