California State Military Department
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Forts Under the Sea
Submarine Mine Defense of San Francisco Bay
by Gordon Chappell
Regional Historian, Pacific West Region
National Park Service
Today the term, "torpedo" means to the average American a self-propelled underwater missile which can be fired from a submarine or launched into the water from the deck of a cruiser, destroyer, patrol torpedo boat, or other vessel, to destroy enemy ships. It was not always so. Historically the term "torpedo" meant what we now know as the underwater explosive mine. Torpedoes of this sort were originally of two basic types: anchored under the sea by cables, they were fired by electrical charges controlled by a switchboard on shore; or they were self-fired by physical contact with an enemy vessel which bumped into them, or in later and more sophisticated versions by magnetic fields, acoustics or other devices triggered by the mere proximity of a vessel. The "contact" torpedo frequently was laid in offshore minefields to deny use of the seaward harbor approaches to enemy vessels, or in enemy waters to block ship channels, and these, once laid, were more or less free agents, anchored in place but not under actual control even of the nation which laid them, other than to the extent that their location was known and mapped. But the kind of torpedo or mine that was fired from shore commonly was used in or just outside the harbor they protected. These were harmless to vessels passing even directly over them, unless that switch on shore was closed to fire them beneath an enemy ship.
Torpedoes, later called mines, were an American invention. An unsuccessful attempt was made to destroy a British warship with one as early as the Revolutionary War. Robert Fulton blew up a small vessel with one early in the 19th Century. In the 1830s and 1840s Samuel Colt, inventor of the revolver, perfected means of firing an underwater explosive charge using electricity, and invented an electrical cable capable of being used under water. Following the Civil War, Lieutenant Colonel. Henry L. Abbot of the Corps of Engineers carried out a long series of experiments in submarine mining at Willets Point, New York, formulating the system that later would be used by engineers in San Francisco Harbor.
Since it was the Corps of Engineers which pioneered in developing torpedo defense systems, responsibility for their installation and management remained for some years with the engineers. In 1903, however, the responsibility was transferred to the Coast Artillery Corps, and it was not until 1949 that responsibility for harbor defense minefields were transferred to the U.S. Navy, only one year before the Coast Artillery Corps was disbanded, air power having left it obsolete.
It was in June 1883 that the first shipment of "buoyant torpedoes" to San Francisco was made, and they temporarily were stored in the pier casemate at Alcatraz, until a concrete torpedo storehouse, completed about 1889, could be planned and built on the northern end of Yerba Buena Island. (The storehouse still stands, nearly beneath the approach of the Bay Bridge to the north side of the island and its highway tunnel.)
Electrically fired "torpedoes" or mines required a control room from which cables ran out into the water and from which an operator sent the electrical impulse to fire the mine. These were termed mine or torpedo casemates. In 1889 funding was provided to construct the first two of these in San Francisco Bay, one on Alcatraz and one at Fort Mason. The Alcatraz casemate was simply an adaptation of part of an existing structure, but an entirely new Fort Mason torpedo casemate was built in 1890, and still exists. Mines were not actually placed until the stimulus of the Spanish American War, when 28 harbors nationwide were mined; among West Coast harbors, San Francisco's was the only one to have that defense. Its first mine was planted on June 11, 1898, and mine planting continued until July 16, when 63 had been emplaced but the armistice of August 12 resulted in subsequent picking up of the mines, which were cleaned and again stored in the Buena storehouse by November 1898.
To plant the mines the army used tugboats, lighters and other small craft until April 16, 1909, when two of the army's first class of especially designed mine planters, the Armistead and the Ringgold steamed through the Golden Gate. Thereafter such special vessels did the work.
Meanwhile, new mining casemates were built and some old ones abandoned. One was added north of Point Cavallo and a fourth near Mortar Hill on Angel Island. In 1897 a fifth was constructed, this one at Quarry Point on Angel Island.
When on March 31, 1903, responsibility for mines in San Francisco Bay transferred from the Corps of Engineers to the Coast Artillery Corps, the artillery command was unhappy with the location of the mine depot on Yerba Buena Island, although Engineers argued that there it was protected by all the defenses of the Bay, including the minefields. But the artillery wanted it relocated farther west, so between 1907 and 1910 a new depot and wharf were built a short distance east of Fort Point. Although poorly located and designed, this depot nevertheless served through World Wars I and II and most of its buildings still stand. New mine casements were built, one at Fort Barry in 1908, one at Fort Baker in 1909, and one at Baker Beach in Fort Winfield Scott in 1912. Planned since 1918, the final modernization was construction of an entirely new mine depot and wharf to supplement and eventually replace the one near Fort Point. Construction began in 1937 on the west side of Horseshoe Bay at Fort Baker and the new depot was essentially finished in 1941. A new mine casement at Baker Beach was built in 1943. The minefields were protected against enemy mine sweepers by rapid fire batteries and searchlights which provided nighttime illumination.
Map Courtesy of Brian Chin
Fields of both shore-controlled mines and some contact mines were planted near San Francisco during the late 1930s and early 1940s, being finished after America entered World War II on December 7, 1941. By the end of the war in 1945 the harbor was protected by 37 mine groups with 13 mines in each group, or 481 mines. But World War II, which brought harbor mine defense to its highest state or perfection, also spelled its doom, for air power demonstrated so effectively in that war left both coast artillery and shore-controlled under water mines obsolete in American defense.
Army mine-planting crew hauls up a seaweed-covered buoyant mine. Each mine carried 800-pounds of TNT and was connected by electric cable to a shore-based detonating station. When a vessel struck a mine, an impact-sensitive device in each mine sounded the alarm in the control bunker. The order could then be given to detonate the mine and blow up the vessel which hit it. Photograph courtesy of Brian Chin

The Army Mine Planter Service
As a result of the Appropriations Act of July 9, 1918, the rank and grade of warrant officer was officially established. War Department Bulletin 43 dated July 22, 1918 stated: " the Coast Artillery Corps of the Regular Army a service to be known as the Army Mine Planter Service, which shall consist, for each mine planter in the service of the United States, of one master, one first mate, one second mate, one chief engineer, one second assistant engineer and one assistant engineer, who shall be warrant officers appointed by holding their office at the discretion of the Secretary of War." Although no warrant officer rank insignia was authorized, a sleeve insignia to identify the job specialties was created by War Department Circular 15 on January 17, 1920. The sleeve insignia had a three-bladed propeller or foul anchor above the braid as shown below. This insignia remained in effect until the Mine Planter Service was abolished on June 30, 1947.


 Chief Engineer

First Mate

 Assistant Engineer

  Second Mate

 Second Assistant Engineer
Those who served at the San Francisco harbor defenses fondly remember the mine planter Niles, one of the most graceful ships to serve in the Army mine planter service. This vessel was equipped with davits and other specialized gear to plant mines and maintain them. The crews which served aboard mine planters were all Army personnel. This ship mounted several .50-caliber machine guns for protection on the high seas. The Niles, along with two other mine planters, were permanently assigned to the San Francisco defenses during World War Two

Photographs courtesy of Brian Chin
Many smaller boats aided the mine planter ships in mining operations off the harbor entrance. Some mine planter soldiers were recruited from the crab fishermen of San Francisco's famed Fisherman's Wharf. Occasionally, in course of their mine planting duties, these men also planted crab pots. The resulting crab bounty provided the dinner for the big gun defense batteries which chipped in for crab bait.

Fort Baker's Mine Depot, now part of the Coast Guard Station, Golden Gate. October 2000



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