GOLDEN GATE UNDERWATER MINEFIELDS

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.

The underwater mines were planted in a semi-circle across the harbor entrance. Double rows of mines went across the shallow bottom of the shoreline and across the main channel. Coast Guard picket boats were also stationed at the main channel to control shipping. A last line of mines was stretched across the Golden Gate itself. Beyond the bridge, the U.S. Navy installed a submarine net.

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