Submarine mines have been part of our arsenal since the American Revolution. On Christmas Day 1776 David Bushnell received permission from General George Washington to release kegs filled with powder into the Delaware River above Philadelphia. Ice floes redirected and slowed the drifting kegs so that they did not reach the British fleet until ten days later. One keg exploded while being retrieved from the water and the British destroyed the others with cannon fire. Known as the Battle of the Kegs, this and other attempts to deploy sea mines resulted in failure, but attempts to develop an effective mine continued.
Robert Fulton invented the word torpedo to describe his underwater explosive device and successfully destroyed a ship in 1805. In the 1840s Samuel Colt began experimenting with underwater mines fired by electric current and in 1842, he blew up an old schooner in the Potomac River from a shore station five miles away.
THE CIVIL WAR
The progression of sea mines slowed until the American Civil War. The Confederate States Navy, being much smaller and having less ordnance to defend the coast, organized a Torpedo Bureau to experiment with and develop underwater explosives. At Mobile Bay Admiral Farragut was heard to declare "damn the torpedoes" but he was lucky that most of the mines did not explode. Other Union vessels were not as lucky. The Confederate States sank 36 Federal ships, nine by cannon and 27 by explosive mines.
The 1885 Fortification Board designed a new coast defense system that included concrete emplacements armed with rifled steel guns. They also recommended that submergible mines be part of the defense system. In 1890 a Mine Board approved 147 mines for the Potomac and planned to place the minefield two miles down river and one mile up river from Digges Point. Underground mine control rooms called casemates were to be placed at Fort Washington and Fort Hunt. Mine operations were under the control of the Army engineers.
The purpose of the torpedo defenses was not to destroy enemy ships. It was believed that a minefield placed 4,000 to 8,000 yards from the main defense would demand that an approaching enemy slow down to navigate through the minefield. At this range the heavy guns were most effective against ship armor. This is also the interior limit of mortar fire so that the 12-inch mortars could be used against the decks an approaching fleet. This distance would also give warning when an enemy ship hit a mine at night or during periods of limited visibility so that other defenses could be activated in time to prevent a run-by.