Harbor Defense of Boston - WWII Underwater Defenses
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During World War II Boston Harbor was protected by a series of underwater defenses that included controlled underwater mines, underwater hydrophones and underwater magnetic loop detectors. Many of the small caliber defenses of Boston Harbor were focused on protecting the minefields from small fast minesweepers and motor torpedo boats. The mine field defenses included 3" gun batteries, 6" gun batteries, 90mm AMTB gun batteries and portable searchlights.
Boston Harbor has two major channels, north and south. Both of these channels were protected with controlled mine fields during the war. The south field had 7 groups of mines while the north field had 23 groups. Three separate mine casemates controlled the mines, one at Fort Warren (2) one Great Brewster Island MR and one at Fort Dawes. Fort Warren (2) controlled 7 groups in the south channel while Great Brewster Island MR controlled 15 groups in the north and Fort Dawes another 8 groups in the north.
The hydrophones and magnetic loop detectors were generally positioned in front of the mine groups to detect approaching ships. Ship tracks were plotted in the plotting rooms of the mine casemates. Control of the minefields came from the mine casemates under a group command. Arming and firing the mines was done in the respective mine casemates. Deactivated gun battery magazines were used to store the mine explosives which totaled some 1,521,000 pounds of TNT required for Boston Harbor mines.