Submarine mines in United States harbor defense

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.

This initiated 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, designated Coast Defense Commands in 1913, defending major seaports.

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.

As was the case with other parts of the U.S. coast defense system (e.g., its thousands of guns), there is no evidence that a mine was ever fired in anger against an attacking enemy, except in the Philippines in 1941-42.

[7] Each protected harbor also maintained a small fleet of mine planters and tenders that were used to plant the mines in precise patterns, haul them back up periodically to check their condition (or to remove them back to the shore for maintenance), and then plant them again.

[8] Each of these harbors also had on-shore facilities to store the mines (called "torpedo storehouses") and the TNT used to fill them, rail systems to load and transport the mines (which often weighed over 750 lb (340 kg) each when loaded), and to test and repair the electrical cables.

These panels were located in the casemate's operating room, pictured at left-center in the plan shown at right.

On the other hand, these types of fire made it much more dangerous for any friendly shipping that might be near the mine field.

Extensive on-shore facilities, as well as a small fleet of mine-planting boats, supported each mine casemate.

Loaded mines were also stored in the underground magazines of those gun batteries which were disarmed about 1925, at the top of the bluff on the northern end of the fort.

These magazines were reached by following the tramway off the map towards the lower left, where it ran up a gradual slope past the "reservoir" (water tower).

Another branch of the tramway track lead to the cable tanks, large concrete tanks filled with seawater pumped from the harbor and used for insulation and conductivity testing of the many miles of electrical cable that were used for mine operations.