Technical Report—Seamines and the U.S. Navy

Although the seamine is a European invention, several Americans have designed variations of this efficient and economical instrument, including David Bushnell (1742-1824), Robert Fulton (1765-1815), Samuel Colt (1814-1862), Edgar Collins Singer (1825-1919), John Mercer Brooke (1826-1906), and Ralph Cowan Browne (1880-1960).

The principle of the seamine was perhaps first applied more than three centuries before the American Declaration of Independence. During the Hundred Years War with France, the British lay siege to the city of Orleans, establishing an outpost at one end of a bridge across the Loire River. In 1429, the French, inspired by Joan of Arc, loaded a boat with fire and let it drift downstream to lodge against the wooden bridge. The destruction of this bridge made it impossible for the British to retreat. As a result, the French withstood and defeated the British at Tourelles, and so the siege came to an end.¹

The Dutch used a more modem boat mine against the Spanish at Antwerp in 1585. The Italian engineer Gianibelli designed and supervised the construction of two boat mines of sufficient size to carry 70-80 tons each of gunpowder and shrapnel material such as marble, millstones, cannon balls, chain shot, iron hooks, and iron caulkers. When the two boats floated down the river, a clock- operated flintlock detonated the gunpowder of one boat at a point where the explosion would destroy a bridge and thus stymie more than 1,000 Spanish troops.²

The essential features of these early boat mines have been applied in this century. In a single boat mine operation at Crete during World War II, the Italians destroyed a British cruiser, two large tankers, and a cargo ship.³ Boat mines were also used by Israel against Egypt in the Israeli War of Independence. In one such attack, the Israelis sank the Egyptian flagship Emir Faruk and severely damaged a minesweeper.⁴

The American Mine Revolution

It is only natural that the American colonists sought to help defeat their British masters with the aid of the Dutch boat mine. David Bushnell made the first proposals. However, the 13 colonies had no central treasury, and they could effect action at sea mainly through the agency of privateers. Bushnell, nevertheless, pursued his ideas for an improved naval seamine in a methodical scientific manner. First he demonstrated that gunpowder kept dry could be detonated underwater.⁵ He then turned his energies to manufacturing a one-man submarine to place such an underwater explosive in a position to damage an enemy ship. He completed the submarine in 1776.

The muscle-power required for the propulsion, guidance, and tactical use of the submarine was the responsibility of its sole occupant—Sergeant Ezra Lee. The first target was HMS Eagle, a copper-sheathed ship of the line carrying 64 guns and the flagship of an English squadron at anchor off Governor’s Island, blockading the entrance and exit to the important New York harbor. Sergeant Lee located and approached his target unobserved. The small submarine carried an encapsulated charge of gunpowder that could be detonated by a 30-minute dock delay mechanism. The charge itself Weighed only 150 pounds—much less than the tons of gunpowder and shrapnel Material carried by the Dutch boat mine. The American explosive charge was, nevertheless, capable of causing great damage or destruction to a ship constructed of oak if the charge could be detonated in contact with the ship’s hull.

After arriving at his target. Sergeant Lee’s first task was to attach his seamine in proximity to HMS Eagle. In modern Practice, such seamines are tied to anchor cables with ropes or suitable chains, or attached to the steel hull of a ship by magnetic devices or by some effective mechanical means. Because of these characteristic attachments, seamines of this type are called “limpets” by analogy with familiar mollusks.

Sergeant Lee intended to drive a cast- iron screw into the wooden hull of the target and position his limpet mine to this screw with a lanyard. However, HMS Eagle’s copper sheathed hull proved impermeable to his screw.⁶ When his available time was about to expire and his endurance all but spent, Lee guided his small submarine away from its intended target. As he departed, however, Lee released his seamine to drift, if it might, against the target. The seamine exploded as scheduled by the clock, but at a point too far from the target to inflict damage.

It later occurred to Bushnell that watertight kegs could be used as seamines. Coopering was an established trade in those days, kegs being used for storing and shipping rum and cut nails, as well as for fermenting cider and other liquors. There was, however, a shortage of kegs. In fact, when kegs for salt became unavailable, it caused a “salt rebellion” in Virginia.

Bushnell reasoned that 20 kegs loaded with gunpowder would be less costly than a boat mine, and that one or two dozen such kegs would be more effective than two boat mines. In 1777, he assembled 20 kegs at Bordentown, New Jersey, and Partially filled each with gunpowder. His plan was to float them down the Delaware River to Philadelphia, where the British fleet lay at anchor.

When loaded with gunpowder, the keg would not float, so it was hung by a lanyard to a fixed depth below a wooden float. The float was trimmed to such a size that the keg and float would drift together with the river current, with the keg submerged and the float inconspicuous at the water surface. Each keg was fitted with an armed spring lock that would detonate the powder charge when the keg banged against the side of a ship. (Both of these features have been useful in more recent times.)

When the kegs drifted down the river, they did not arrive at the Philadelphia anchorage during the hours of darkness, as had been hoped. The trip was long, and winter ice impeded progress. Their arrival on 5 January 1778 was observed, and many were destroyed by musket fire from the ships. Several British sailors attempted to recover one of the drifting kegs, and four of them perished when it exploded—an early indication of the need to develop trained demolition teams to disarm captured seamines.⁷

In addition to delaying the movement of the British warships, the explosions caused panic on board the ships and among inhabitants of the city itself. Citizens and seamen fired their muskets at many floating objects in the river. (During the 20th century, drifting mines have been used to damage and sink ships in Korea, Vietnam, the Arab-Israeli wars, and in the Persian Gulf.)

The Post-Revolutionary Period

Robert Fulton was just 12 years old when Bushnell’s kegs were floated down the Delaware, but he was impressed by the serious consequences that might have resulted had Bushnell’s kegs been better designed and the attack more skillfully managed. Throughout his life, he expressed his mechanical skill in engineering improvements to Bushnell’s drifting kegs and one-man submarines for delivering limpet mines. (Fulton was also widely known as the inventor of the first American steamboat, the Clermont, also known as “Fulton’s Folly” because it required 33 hours to steam a distance of 150 miles.)

In spite of discouraging setbacks, Fulton built three types of attack submarines during his 50 years. In 1797, when the French faced a British armada of 1,000 fighting ships, he persuaded the French government to finance the construction of his first design. Similar in principle to Bushnell’s submarine, it was completed in the spring of 1801. In August, a limpet mine carried by the submarine destroyed an old schooner used as a target. While the first submarine was being built, Napoleon commanded the French attempt to conquer Egypt. But the failure of this undertaking and the loss of the French fleet to Britain proved that Napoleon’s great genius was appropriate for land warfare only. Without the influence of Napoleon, the French declined to support further experiments with Fulton’s limpetcarrying submarine. He then tried to sell the design to England, but the British had the greatest navy in the world, and did not want to sponsor the development of a device that might revolutionize naval warfare to Britain’s disadvantage. Fulton returned to the United States in 1806.⁸

Fulton’s two U. S. submarines greatly influenced later events, particularly in World War II against Japan. His first U. S. construction was similar to the original Bushnell submarine. In 1813 it was used to attack HMS Ramillies anchored in the harbor at New London, Connecticut. The pilot reached the side of his target and tried to attach the limpet next to the ship’s hull, but the cast-iron screw would not penetrate the protective copper sheathing on the hull. In time, he managed to bore a hole through the copper and forced the screw into the wooden hull. As the pilot was about to complete the mission, the screw broke. With no alternative way to attach the limpet, the pilot departed.⁹

Fulton’s second U. S. submarine had a gross weight of 100 tons, a six-foot draft, and did not advance entirely submerged. Extending as much as a foot above the surface, the turtle-shaped vessel towed five seamines, each of which was fitted with a gunlock to detonate its charge of gunpowder upon demand. When one of the seamines met an object believed to be a target, it could be individually detonated by a tug on a wire that engaged the gunlock. (Fifty years later, the H. L. Hunley submarine initially used similar armament—a floating seamine towed astern on a 100-foot line. This weapon system was replaced by a bow-mounted spar torpedo when it was determined that the depth of water in the Charleston area would not allow the attack submarine to navigate under the keel of the Union ships.)

Several turtle submarines of this design were built, one of which destroyed a 200-ton ship in a test at New York. Another was caught in a gale off Long Island, New York, on 26 June 1814, as it was proceeding to attack a group of English ships. The crews of two of the anchored ships, HMS Maidstone and HMS Sylph, attacked the stranded submarine, wrecking it beyond further use.¹⁰

Another device that was not initially appreciated was Fulton’s moored contact mine. It consisted of a copper case containing 100 pounds of gunpowder and a cork-filled wooden box attached below it for buoyancy. A brass box mounted on top of the case was fitted with a firing lever. When the firing lever came in contact with a target, the triggering mechanism fired a musket charge into the main explosive within the case. The seamine assembly was moored at a suitable depth below the surface, held in position by some heavy body or anchor. It was held in position for a predetermined time, even as long as 30 days. At the end of that interval, the firing lever was locked in place and the anchor was released. The buoyant seamine then rose to the surface where it could be handled without hazard.¹¹ Such features for sterilization and rendering safe are characteristic of contemporary seamines.

Samuel Colt developed the electrically controlled seamine. The case for the control mine had to be connected by means of an insulated cable to an operator’s post ashore. At the post it was necessary to provide a cell of the kind first described by the Italian Luigi Galvani with two dissimilar metals immersed in a bath of water and salt. It was necessary to terminate the cable in a coil of wire fine enough to be heated sufficiently by a weak galvanic current to detonate the gunpowder. These requirements were solved satisfactorily by Colt, and, indeed, control mines have been used with various measures of effectiveness by the British, Germans, Viet Cong, and in 1988 by the Swedes.¹²

Colt succeeded near the end of his studies in exploding a control mine nearly five miles from his observation post ashore.¹³ He demonstrated that the best time to close the actuating switch was when the seamine case first came in contact with its target. The Confederates used his electrical means to explode seamines against known targets not long after he died on 10 January 1862, shortly after the Civil War began.

The Civil War

Other Americans made contributions to the advancement of seamine warfare, some of which had lasting import. One was the Singer seamine, used to sink the monitor Tecumseh at Mobile Bay in August 1864.¹⁴ Invented by Edgar Collins Singer, nephew of the inventor of the famous sewing machine, the mine was produced by the E. C. Singer Company for the Confederate “torpedo” service. For this service he was paid $50 Confederate for a single seamine, $150 for a battery of five seamines, and he received a large percentage of the value of the property destroyed by his seamines. (Robert Fulton proposed similar compensation to the French 66 years earlier.)

The Singer mine encased only 60 pounds of gunpowder and it was moored from an anchor of such a weight that it could be planted from a boat by hand. The force of impact with a target ship dislodged a mass of considerable negative buoyancy from the top of the case. This mass was connected by a small chain to a spring-loaded plunger. The plunger was released by a jerk from the falling weight onto the chain, and a spring drove it into a chemical fuse. The fuse ignited and the seamine exploded. A short chain prevented the release of the spring-loaded plunger while the seamine was being planted. After the Singer seamine was in the water, however, it was armed by removing a pin.

John Mercer Brooke anticipated the need for antisweeping devices before countermeasures were generally appreciated. Aside from this antisweeping feature, Brooke’s seamine was merely a simple case containing the conventional charge of 100 pounds of gunpowder intended to explode on impact. It was designed for use against coastal ships and minesweepers of shallow draft. The case was mounted at the top of a solid spar; the other end of this spar was attached to a simple anchor by a metal ring. On occasion, a wire connected to the solid spar was attached to a second case lying on the bottom that enclosed a large charge of gunpowder and was actuated by pulling the wire. The actuating jerk would occur when attempts were made to sweep the seamine near the surface. The charge of the second seamine, even as it lay on the bottom, was sufficient to destroy the minesweeper.¹⁵ The antisweeping principle was an important defensive measure during the Civil War, and has been a design objective of seamines during the 20th century.

During the war. Union forces were astonished to discover effective Confederate seamines at coastal cities such as Wilmington, Charleston, and Mobile, as well as in waterways such as the Potomac, James, Roanoke, Savannah, Mississippi, St. Johns, Cape Fear, Red, and Yazoo rivers. Both moored mines and control mines were planted, and some of both kinds broke loose to pose threats as drifting mines. There were as many as 90 planted at Mobile, 200 at Wilmington, and 20 at Charleston. The Confederate seamines sank 23 Union ships and damaged eight, and sank three of their own ships.¹⁶ In contrast, records indicate that only one Confederate ship succumbed to attack by a Union seamine, at Plymouth, Massachusetts. The Confederate sea- mines delayed the movement of Union ships, as did the actions of the Union crews to deploy countermeasures. The Confederates moved the posts from which the control mines were operated from place to place, especially at night. (In Vietnam in the 1960s, this practice was used by the Viet Cong on the banks of rivers, where the post was covered with bamboo or brush. There, Viet Cong operators of the control mines were able to damage many U. S. riverine boats and minesweepers, because the crews of the Patrol ships could not locate and destroy the control post before the seamines were detonated.)

The U. S. Civil War alerted the world to extended applications of seamine warfare. Nations all over the world began to manufacture their own designs of moored contact and control mines. One moored contact mine, known as the Bustamente seamine, had the shape of a funnel. The funnel shape was approximately 32 inches in diameter at the top, 12 and one- half inches at the bottom, and 36 inches long. The case had a central axial hole in it 11% inches in diameter, for insertion of a cylinder containing 100 pounds of gunpowder. There was space above the explosive charge for a container of dry primer made of gun cotton and another cylinder with six plungers equally spaced around its circumference. These plungers converged at the center to a glass tube filled with sulphuric acid. Their outer ends were in contact with plungers operated by six contact arms on the outside of the seamine case. When a contact arm was struck by a passing vessel, the affected plunger would break the glass tube, and the acid would saturate the chlorate of potash, sugar, and fulminate, and detonate the explosive charge. The container of dry powder and the cylinder with the glass tube and plungers could be stored separately from the main charge. An anchor with a reel of 120 feet of cable was attached to the bottom of the case, allowing the seamine to be moored at a predetermined depth below the surface.

Another design known as the Latimer-Clark device was an elementary control mine consisting of two massive pieces of cast iron. The bottom was an open box 36 by 36 inches and 20 inches deep. The watertight cast-iron cover sealed in a 500-pound charge of gunpowder.¹⁷

The Spanish-American War

The U. S. Navy first encountered foreign seamines during the Spanish-American War of 1898. They were used by the Spanish Navy in the Philippines and in Cuba at Guantanamo and Santiago. Rear Admiral William T. Sampson, Commander U. S. Naval Force, sailed with his ships toward Cuba to engage the Spanish. Spanish Admiral Pascual Cervera planned to protect his fleet and entrap the invasion fleet in the harbor at Santiago. The characteristics of this anchorage were ideal for his purpose. The inlet from the sea extended four miles to the anchorage; there was plenty of room for all of the ships of the Spanish fleet. The hilly sides of the inlet were suitable for gun emplacements. The width of the opening to the sea was merely 125 yards, beyond which an island protected the fleet from view.

The American force did not know to what extent the natural advantages of the harbor had been reinforced. The ship’s crew could see Fort Morro on the eastern bluff overlooking the constricted entrance and could expect gun activity from the hills, but they could not see the seamines hidden below the surface of the waterway.

Admiral Sampson sensed the hazard. It was suggested that the Spanish fleet could be kept within the harbor by sinking just one ship across the narrow channel. For this purpose, Sampson designated the 7,000-ton collier SS Merrimac to be sunk. Stokers worked all night to build up a big head of steam in the Merrimac's boilers, and Lieutenant R. P. Plobson and seven crewmen volunteered to sink the ship.

On 3 June, several hours before sunrise, the volunteers and the Merrimac proceeded to the channel entrance and waited for the incoming tide. Soon after the ship entered the channel, a loud explosion rocked the ship, then another. Spaniards positioned on the bank had observed the approach of the Merrimac and had fired two control mines from their posts. Nearby guns began to blaze. Then, another explosion all but lifted the collier out of the water. She began to sink. As the tidal current swung the ship across the channel passage, a boat in a small cove came close and fired its guns at the stem of the ship. The rudder was damaged, and the chain by which the stem could have been anchored broke. The ship swung in its arc further than was intended, so the channel passage was merely narrowed, not closed. There, battered on port, starboard, and underside, the collier was sunk by the crew until she rested on the bottom. The stranded volunteers were picked up by the Spaniards and imprisoned for six weeks. Admiral Cervera sent a brief note to Admiral Sampson commending the sailors’ bravery.¹⁸

On 3 July, Cervera attempted to escape with his fleet. He assembled his crews and refueled his ships. The electric wire connections to the seven remaining control mines were removed and four moored contact mines were removed from one side of the channel. A boom of floating logs was swung out of the way. In the darkness of the night, his ships passed astern of the Merrimac and escaped through the passage to the open sea. After the ships passed the minefields, the electrical connections were remade, and the four contact mines were replanted in their original places. American observers spotted the departing ships, which were taken under fire. They turned and rammed themselves onto the shores of the land where crewmen hoped to save their lives if not their ships. All of the Spanish ships were destroyed by early afternoon.

Santiago did not issue a formal surrender until two weeks after the Spanish ships were destroyed. Immediately upon receiving the surrender, Sampson sent men ashore to investigate the defenses of the harbor. In particular, he had them investigate the number and types of seamines used; samples were transported to the United States for study. Nine moored contact mines had been planted, five on one side of the channel and four on the other. This line of Bustamente seamines crossed the channel in the vicinity of where the Merrimac was sunk, but none of the contact mines had exploded. Eight were recovered by the USS Suwanee. Two lines of Latimer-Clark control mines had been placed along the channel with five seamines in each line. Each group was controlled separately by operators on opposite sides of the channel. Three seamines were detonated during passage of the Merrimac, two were detonated subsequently by the U. S. Navy, and five were recovered.¹⁹

The Cuban experience directed the U. S. Navy’s attention to three important matters related to seamine warfare. First, operations in foreign waters should never be undertaken without having countermeasures ships available. The Navy could not enter Guantanamo Bay until minesweepers were brought from the United States. (In Korea, military troops carried on board ship were delayed from landing for eight days while seamine countermeasures forces were being strengthened in the Wonsan area. In March 1987, expanding U. S. Navy responsibilities in the Persian Gulf were announced. During the following May, June, and July, ships were damaged there by Iranian seamines. Yet, it required several months to ready and tow six minesweepers from Seattle and Charleston to the Persian Gulf. It was perhaps October before all these minesweepers were on station to sweep simple moored contact mines in the threatened areas of the Gulf.)

Second, other weapon systems can be used effectively in support of defensive minefields. At Santiago, these support weapons included machine guns on camouflaged carriages, riflemen concealed by brush on each side of the entrance, and torpedo-armed ships hidden in coves adjacent to the channel.

Third, ships taken up from the trade, such as the Merrimac, can be essential in the prosecution of sea warfare. Ships used as minesweepers are less expensive than U. S. Navy combatants. (In the Falklands Conflict, Britain used stern trawlers from the trade to sweep seamines planted by Argentina in the approaches to the capital city of Stanley.²⁰)