Submarine mines in United States harbor defense

The modern era of defending American harbors with submarine mines (originally referred to as "torpedoes") began in the post-Civil War period.

In 1866, the United States Army Corps of Engineers established the Engineer School of Application at Willets Point, NY (later named Fort Totten). The first commander of this School, Major Henry Larcom Abbot, was almost single-handedly responsible for designing and supervising the program of research and development that defined the strategy and tactics for the mine defense of American harbors. Abbot experimented with underwater explosives, fuzes, cabling, and electrical equipment for over a decade before publishing the first manuals on the use of mines in coast defense in 1876–77.

Then, in 1886, the Endicott Board made its report on harbor defense, initiating a vast expansion in the building of modern forts, the installation of new guns, and the preparation of mine defenses at newly created Artillery Districts, later designated Coast Defense Commands, defending major seaports.

From about 1900 until 1946 the mine defense program grew, until upwards of 10,000 controlled mines were maintained by the United States Army Coast Artillery Corps. In July 1918, the U.S. Army Mine Planter Service (AMPS) was established to maintain U.S. mine defenses.

Controlled mines were anchored to the bottom of a harbor, either sitting on the bottom itself (ground mines) or floating (buoyant mines) at depths which could vary widely, from about 20 to 250 feet (6–75 m). These mines were fired electrically through a vast network of underwater electrical cables at each protected harbor. Mines could be set to explode on contact or be triggered by the operator, based on reports of the position of enemy ships. The networks of cables terminated on shore in massive concrete bunkers called mine casemates (see photo, below right), that were usually buried beneath protective coverings of earth.

The mine casemate housed electrical generators, batteries, control panels, and troops that were used to test the readiness of the mines and to fire them when needed. The map of Boston Harbor's mine fields (below right) shows the harbor mine defenses consisting of 30 groups of mines, with 19 mines per group. Each mine was normally loaded with 200 lb (91 kg) of TNT. So in Boston's case, a total of 57 tons of explosives guarded the harbor.

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