A naval mine is a self-contained
Although international law requires signatory nations to declare mined areas, precise locations remain secret; and non-complying individuals may not disclose minelaying. While mines threaten only those who choose to traverse waters that may be mined, the possibility of activating a mine is a powerful disincentive to shipping. In the absence of effective measures to limit each mine's lifespan, the hazard to shipping can remain long after the war in which the mines were laid is over. Unless detonated by a parallel time fuze at the end of their useful life, naval mines need to be found and dismantled after the end of hostilities; an often prolonged, costly, and hazardous task.
Modern mines containing
Mines can be laid in many ways: by purpose-built minelayers, refitted ships, submarines, or aircraft—and even by dropping them into a harbour by hand. They can be inexpensive: some variants can cost as little as US$2,000, though more sophisticated mines can cost millions of dollars, be equipped with several kinds of sensors, and deliver a warhead by rocket or torpedo.
Their flexibility and cost-effectiveness make mines attractive to the less powerful belligerent in asymmetric warfare. The cost of producing and laying a mine is usually between 0.5% and 10% of the cost of removing it, and it can take up to 200 times as long to clear a minefield as to lay it. Parts of some World War II naval minefields still exist because they are too extensive and expensive to clear. Some 1940s-era mines may remain dangerous for many years.
Mines have been employed as offensive or defensive weapons in rivers, lakes, estuaries, seas, and oceans, but they can also be used as tools of psychological warfare. Offensive mines are placed in enemy waters, outside harbours, and across important shipping routes to sink both merchant and military vessels. Defensive minefields safeguard key stretches of coast from enemy ships and submarines, forcing them into more easily defended areas, or keeping them away from sensitive ones.
Shipowners are reluctant to send their ships through known minefields. Port authorities may attempt to clear a mined area, but those without effective minesweeping equipment may cease using the area. Transit of a mined area will be attempted only when strategic interests outweigh potential losses. The decision-makers perception of the minefield is a critical factor. Minefields designed for psychological effect are usually placed on trade routes to stop ships from reaching an enemy nation. They are often spread thinly, to create an impression of minefields existing across large areas. A single mine inserted strategically on a shipping route can stop maritime movements for days while the entire area is swept. A mine's capability to sink ships makes it a credible threat, but minefields work more on the mind than on ships.
International law, specifically the Eighth Hague Convention of 1907, requires nations to declare when they mine an area, to make it easier for civil shipping to avoid the mines. The warnings do not have to be specific; for example, during World War II, Britain declared simply that it had mined the English Channel, North Sea and French coast.
Precursors to naval mines were first invented by Chinese innovators of
The first plan for a sea mine in the West was by Ralph Rabbards, who presented his design to Queen
The 1804 Raid on Boulogne made extensive use of explosive devices designed by inventor Robert Fulton. The 'torpedo-catamaran' was a coffer-like device balanced on two wooden floats and steered by a man with a paddle. Weighted with lead so as to ride low in the water, the operator was further disguised by wearing dark clothes and a black cap. His task was to approach the French ship, hook the torpedo to the anchor cable and, having activated the device by removing a pin, remove the paddles and escape before the torpedo detonated. Also to be deployed were large numbers of casks filled with gunpowder, ballast and combustible balls. They would float in on the tide and on washing up against an enemy's hull, explode. Also included in the force were several fireships, carrying 40 barrels of gunpowder and rigged to explode by a clockwork mechanism.
In 1812, Russian engineer
In the 19th century, mines were called
After 1865 the United States adopted the mine as its primary weapon for
During the War of the Pacific (1879-1883), the Peruvian Navy, at a time when the Chilean squadron was blockading the Peruvian ports, formed a brigade of torpedo boats under the command of the frigate captain Leopoldo Sánchez Calderón and the Peruvian engineer Manuel Cuadros, who perfected the naval torpedo or mine system to be electrically activated when the cargo weight was lifted. This is how, on July 3, 1880, in front of the port of Callao, the gunned transport Loa flies when capturing a sloop mined by the Peruvians. A similar fate occurred with the gunboat schooner Covadonga in front of the port of Chancay, on September 13, 1880, which having captured and checked a beautiful boat, it exploded when hoisting it on its side.
Early 20th century
The next major use of mines was during the
Following the end of the Russo-Japanese War, several nations attempted to have mines banned as weapons of war at the
Many early mines were fragile and dangerous to handle, as they contained glass containers filled with nitroglycerin or mechanical devices that activated a blast upon tipping. Several mine-laying ships were destroyed when their cargo exploded.
Beginning around the start of the 20th century, submarine mines played a major role in the defense of U.S. harbours against enemy attacks as part of the Endicott and Taft Programs. The mines employed were controlled mines, anchored to the bottoms of the harbours, and detonated under control from large mine casemates onshore.
During World War I, mines were used extensively to defend coasts, coastal shipping, ports and naval bases around the globe. The Germans laid mines in shipping lanes to sink merchant and naval vessels serving Britain. The Allies targeted the German U-boats in the Strait of Dover and the Hebrides. In an attempt to seal up the northern exits of the North Sea, the Allies developed the North Sea Mine Barrage. During a period of five months from June 1918, almost 70,000 mines were laid spanning the North Sea's northern exits. The total number of mines laid in the North Sea, the British East Coast, Straits of Dover, and Heligoland Bight is estimated at 190,000 and the total number during the whole of WWI was 235,000 sea mines. Clearing the barrage after the war took 82 ships and five months, working around the clock. It was also during World War I, that the British hospital ship, HMHS Britannic, became the largest vessel ever sunk by a naval mine. The Britannic was the sister ship of the RMS Titanic, and the RMS Olympic.
World War II
During World War II, the U-boat fleet, which dominated much of the battle of the Atlantic, was small at the beginning of the war and much of the early action by German forces involved mining convoy routes and ports around Britain. German submarines also operated in the Mediterranean Sea, in the Caribbean Sea, and along the U.S. coast.
Initially, contact mines (requiring a ship to physically strike a mine to detonate it) were employed, usually tethered at the end of a cable just below the surface of the water. Contact mines usually blew a hole in ships' hulls. By the beginning of World War II, most nations had developed mines that could be dropped from aircraft, some of which floated on the surface, making it possible to lay them in enemy harbours. The use of dredging and nets was effective against this type of mine, but this consumed valuable time and resources and required harbours to be closed.
Later, some ships survived mine blasts, limping into port with buckled plates and broken backs. This appeared to be due to a new type of mine, detecting ships by their proximity to the mine (an influence mine) and detonating at a distance, causing damage with the shock wave of the explosion. Ships that had successfully run the gantlet of the Atlantic crossing were sometimes destroyed entering freshly cleared British harbours. More shipping was being lost than could be replaced, and Churchill ordered the intact recovery of one of these new mines to be of the highest priority.
The British experienced a stroke of luck in November 1939, when a German mine was dropped from an aircraft onto the mudflats off Shoeburyness during low tide. Additionally, the land belonged to the army and a base with men and workshops was at hand. Experts were dispatched from HMS Vernon to investigate the mine. The Royal Navy knew that mines could use magnetic sensors, Britain having developed magnetic mines in World War I, so everyone removed all metal, including their buttons, and made tools of non-magnetic brass. They disarmed the mine and rushed it to the labs at HMS Vernon, where scientists discovered that the mine had a magnetic arming mechanism. A large ferrous object passing through the Earth's magnetic field will concentrate the field through it, due to its magnetic permeability; the mine's detector was designed to trigger as a ship passed over when the Earth's magnetic field was concentrated in the ship and away from the mine. The mine detected this loss of the magnetic field which caused it to detonate. The mechanism had an adjustable sensitivity, calibrated in milligauss.
From this data, known methods were used to clear these mines. Early methods included the use of large electromagnets dragged behind ships or below low-flying aircraft (a number of older bombers like the Vickers Wellington were used for this). Both of these methods had the disadvantage of "sweeping" only a small strip. A better solution was found in the "Double-L Sweep" using electrical cables dragged behind ships that passed large pulses of current through the seawater. This created a large magnetic field and swept the entire area between the two ships. The older methods continued to be used in smaller areas. The Suez Canal continued to be swept by aircraft, for instance.
While these methods were useful for clearing mines from local ports, they were of little or no use for enemy-controlled areas. These were typically visited by warships, and the majority of the fleet then underwent a massive degaussing process, where their hulls had a slight "south" bias induced into them which offset the concentration-effect almost to zero.
Initially, major warships and large troopships had a copper degaussing coil fitted around the perimeter of the hull, energized by the ship's electrical system whenever in suspected magnetic-mined waters. Some of the first to be so fitted were the carrier HMS Ark Royal and the liners RMS Queen Mary and RMS Queen Elizabeth. It was a photo of one of these liners in New York harbour, showing the degaussing coil, which revealed to German Naval Intelligence the fact that the British were using degaussing methods to combat their magnetic mines. This was felt to be impractical for smaller warships and merchant vessels, mainly because the ships lacked the generating capacity to energise such a coil. It was found that "wiping" a current-carrying cable up and down a ship's hull temporarily canceled the ships' magnetic signature sufficiently to nullify the threat. This started in late 1939, and by 1940 merchant vessels and the smaller British warships were largely immune for a few months at a time until they once again built up a field.
The cruiser HMS Belfast is just one example of a ship that was struck by a magnetic mine during this time. On 21 November 1939, a mine broke her keel, which damaged her engine and boiler rooms, as well as injuring 46 men with one man later dying from his injuries. She was towed to Rosyth for repairs. Incidents like this resulted in many of the boats that sailed to Dunkirk being degaussed in a marathon four-day effort by degaussing stations.
The Allies and Germany deployed acoustic mines in World War II, against which even wooden-
The Germans developed a pressure-activated mine and planned to deploy it as well, but they saved it for later use when it became clear the British had defeated the magnetic system. The U.S. also deployed these, adding "counters" which would allow a variable number of ships to pass unharmed before detonating. This made them a great deal harder to sweep.
Mining campaigns could have devastating consequences. The U.S. effort against Japan, for instance, closed major ports, such as Hiroshima, for days, and by the end of the Pacific War had cut the amount of freight passing through Kobe–Yokohama by 90%.
When the war ended, more than 25,000 U.S.-laid mines were still in place, and the Navy proved unable to sweep them all, limiting efforts to critical areas. After sweeping for almost a year, in May 1946, the Navy abandoned the effort with 13,000 mines still unswept. Over the next thirty years, more than 500 minesweepers (of a variety of types) were damaged or sunk clearing them.
The U.S. began adding delay counters to their magnetic mines in June 1945.
Cold War era
Since World War II, mines have damaged 14 United States Navy ships, whereas air and missile attacks have damaged four. During the Korean War, mines laid by North Korean forces caused 70% of the casualties suffered by U.S. naval vessels and caused 4 sinkings.
In the summer of 1984, magnetic sea mines damaged at least 19 ships in the Red Sea. The U.S. concluded Libya was probably responsible for the minelaying. In response the U.S., Britain, France, and three other nations launched Operation Intense Look, a minesweeping operation in the Red Sea involving more than 46 ships.
On the orders of the
Post Cold War
In the first month of the 2022 Russian invasion of Ukraine, Ukraine accused Russia of deliberately employing drifting mines in the Black Sea area. Around the same time, Turkish and Romanian military diving teams were involved in defusing operations, when stray mines were spotted near the coasts of these countries. London P&I Club issued a warning to freight ships in the area, advising them to "maintain lookouts for mines and pay careful attention to local navigation warnings". Ukrainian forces have mined "from the Sea of Azov to the Black Sea which banks the critical city of Odesa." 
A-underwater, B-bottom, SS-submarine. 1-drifting mine, 2-drifting mine, 3-moored mine, 4-moored mine (short wire), 5-bottom mines, 6-torpedo mine/CAPTOR mine, 7-rising mine
Naval mines may be classified into three major groups; contact, remote and influence mines.
The earliest mines were usually of this type. They are still used today, as they are extremely low cost compared to any other anti-ship weapon and are effective, both as a psychological weapon and as a method to sink enemy ships. Contact mines need to be touched by the target before they detonate, limiting the damage to the direct effects of the explosion and usually affecting only the vessel that triggers them.
Early mines had mechanical mechanisms to detonate them, but these were superseded in the 1870s by the "Hertz horn" (or "chemical horn"), which was found to work reliably even after the mine had been in the sea for several years. The mine's upper half is studded with hollow lead protuberances, each containing a glass vial filled with sulfuric acid. When a ship's hull crushes the metal horn, it cracks the vial inside it, allowing the acid to run down a tube and into a lead–acid battery which until then contained no acid electrolyte. This energizes the battery, which detonates the explosive.
Earlier forms of the detonator employed a vial of sulfuric acid surrounded by a mixture of potassium perchlorate and sugar. When the vial was crushed, the acid ignited the perchlorate-sugar mix, and the resulting flame ignited the gunpowder charge.
During the initial period of World War I, the Royal Navy used contact mines in the English Channel and later in large areas of the North Sea to hinder patrols by German submarines. Later, the American antenna mine was widely used because submarines could be at any depth from the surface to the seabed. This type of mine had a copper wire attached to a buoy that floated above the explosive charge which was weighted to the seabed with a steel cable. If a submarine's steel hull touched the copper wire, the slight voltage change caused by contact between two dissimilar metals was amplified[clarification needed] and detonated the explosives.
Limpet mines are a special form of contact mine that are manually attached to the target by magnets and remain in place. They are named because of the similarity to the
Moored contact mines
Generally, this type of mine is set to float just below the surface of the water or as deep as five meters. A steel cable connecting the mine to an anchor on the seabed prevents it from drifting away. The explosive and detonating mechanism is contained in a buoyant metal or plastic shell. The depth below the surface at which the mine floats can be set so that only deep draft vessels such as aircraft carriers, battleships or large cargo ships are at risk, saving the mine from being used on a less valuable target. In
Floating mines typically have a mass of around 200 kg (440 lb), including 80 kg (180 lb) of explosives e.g.
Moored contact mines with plummet
A special form of moored contact mines are those equipped with a plummet. When the mine is launched (1), the mine with the anchor floats first and the lead plummet sinks from it (2). In doing so, the plummet unwinds a wire, the deep line, which is used to set the depth of the mine below the water surface before it is launched (3). When the deep line has been unwound to a set length, the anchor is flooded and the mine is released from the anchor (4). The anchor begins to sink and the mooring cable unwinds until the plummet reaches the sea floor (5). Due to the decreasing tension on the deep line, the mooring cable is clamped. The anchor sinks further down to the bottom of the sea pulling the mine as deep below the water surface as the deep line has been unwound (6). Thus, even without knowing the exact depth, an exact depth of the mine below the water surface can be set, limited only by the maximum length of the mooring cable.
Drifting contact mines
Drifting mines were occasionally used during World War I and World War II. However, they were more feared than effective. Sometimes floating mines break from their moorings and become drifting mines; modern mines are designed to deactivate in this event. After several years at sea, the deactivation mechanism might not function as intended and the mines may remain live. Admiral Jellicoe's British fleet did not pursue and destroy the outnumbered German High Seas Fleet when it turned away at the Battle of Jutland because he thought they were leading him into a trap: he believed it possible that the Germans were either leaving floating mines in their wake, or were drawing him towards submarines, although neither of these was the case.
After World War I the drifting contact mine was banned, but was occasionally used during World War II. The drifting mines were much harder to remove than tethered mines after the war, and they caused about the same damage to both sides.
Churchill promoted "Operation Royal Marine" in 1940 and again in 1944 where floating mines were put into the Rhine in France to float down the river, becoming active after a time calculated to be long enough to reach German territory.
Remotely controlled mines
Frequently used in combination with coastal artillery and hydrophones, controlled mines (or command detonation mines) can be in place in peacetime, which is a huge advantage in blocking important shipping routes. The mines can usually be turned into "normal" mines with a switch (which prevents the enemy from simply capturing the controlling station and deactivating the mines), detonated on a signal or be allowed to detonate on their own. The earliest ones were developed around 1812 by Robert Fulton. The first remotely controlled mines were moored mines used in the American Civil War, detonated electrically from shore. They were considered superior to contact mines because they did not put friendly shipping at risk. The extensive American fortifications program initiated by the Board of Fortifications in 1885 included remotely controlled mines, which were emplaced or in reserve from the 1890s until the end of World War II.
These mines are triggered by the influence of a ship or submarine, rather than direct contact. Such mines incorporate
First used during WWI, their use became more general in WWII. The sophistication of influence mine fuses has increased considerably over the years as first
Modern influence mines such as the
Even as far back as WWII it was possible to incorporate a "ship counter" function in mine fuzes. This might set the mine to ignore the first two ships passing over it (which could be minesweepers deliberately trying to trigger mines) but detonate when the third ship passes overhead, which could be a high-value target such as an
The moored mine is the backbone of modern mine systems. They are deployed where water is too deep for bottom mines. They can use several kinds of instruments to detect an enemy, usually a combination of acoustic, magnetic and pressure sensors, or more sophisticated optical shadows or electro potential sensors. These cost many times more than contact mines. Moored mines are effective against most kinds of ships. As they are cheaper than other anti-ship weapons they can be deployed in large numbers, making them useful
Bottom mines (sometimes called ground mines) are used when the water is no more than 60 meters (200 feet) deep or when mining for submarines down to around 200 meters (660 feet). They are much harder to detect and sweep, and can carry a much larger warhead than a moored mine. Bottom mines commonly use multiple types of sensors, which are less sensitive to sweeping.
These mines usually weigh between 150 and 1,500 kg (330 and 3,310 lb), including between 125 and 1,400 kg (276 and 3,086 lb) of explosives.
Several specialized mines have been developed for other purposes than the common minefield.
The bouquet mine is a single anchor attached to several floating mines. It is designed so that when one mine is swept or detonated, another takes its place. It is a very sensitive construction and lacks reliability.
The anti-sweep mine is a very small mine (40 kg (88 lb) warhead) with as small a floating device as possible. When the wire of a mine sweep hits the anchor wire of the mine, it drags the anchor wire along with it, pulling the mine down into contact with the sweeping wire. That detonates the mine and cuts the sweeping wire. They are very cheap and usually used in combination with other mines in a minefield to make sweeping more difficult. One type is the Mark 23 used by the United States during World War II.
The mine is hydrostatically controlled to maintain a pre-set depth below the water's surface independently of the rise and fall of the tide.
The ascending mine is a floating distance mine that may cut its mooring or in some other way float higher when it detects a target. It lets a single floating mine cover a much larger depth range.
These are mines containing a moving weapon as a warhead, either a torpedo or a rocket
A Russian invention, the rocket mine is a bottom distance mine that fires a homing high-speed rocket (not torpedo) upwards towards the target. It is intended to allow a bottom mine to attack surface ships as well as submarines from a greater depth. One type is the Te-1 rocket propelled mine.
A torpedo mine is a self-propelled variety, able to lie in wait for a target and then pursue it e.g. the
The mine is propelled to its intended position by propulsion equipment such as a torpedo. After reaching its destination, it sinks to the seabed and operates like a standard mine. It differs from the homing mine in that its mobile stage is set before it lies in wait, rather than as part of the attacking phase.
One such design is the Mk 67 submarine-launched mobile mine (which is based on a Mark 37 torpedo), capable of traveling as far as 16 km (10 mi) through or into a channel, harbour, shallow water area, and other zones which would normally be inaccessible to craft laying the device. After reaching the target area they sink to the sea bed and act like conventionally laid influence mines.
During the Cold War, a test was conducted with a naval mine fitted with tactical nuclear warheads for the "Baker" shot of Operation Crossroads. This weapon was experimental and never went into production. There have been some reports that North Korea may be developing a nuclear mine. The Seabed Arms Control Treaty prohibits the placement of nuclear weapons on the seabed beyond a 12-mile coast zone.
This comprises two moored, floating contact mines which are tethered together by a length of steel cable or chain. Typically, each mine is situated approximately 18 m (60 ft) away from its neighbor, and each floats a few meters below the surface of the ocean. When the target ship hits the steel cable, the mines on either side are drawn down the side of the ship's hull, exploding on contact. In this manner it is almost impossible for target ships to pass safely between two individually moored mines. Daisy-chained mines are a very simple concept which was used during World War II. The first prototype of the Daisy-chained mine and the first combat use came in Finland, 1939.
Plastic drums filled with sand or concrete are periodically rolled off the side of ships as real mines are laid in large mine-fields. These inexpensive false targets (designed to be of a similar shape and size as genuine mines) are intended to slow down the process of mine clearance: a mine-hunter is forced to investigate each suspicious sonar contact on the sea bed, whether it is real or not. Often a maker of naval mines will provide both training and dummy versions of their mines.
Historically several methods were used to lay mines. During WWI and WWII, the Germans used U-boats to lay mines around the UK. In WWII, aircraft came into favour for mine laying with one of the largest examples being the mining of the Japanese sea routes in Operation Starvation.
Laying a minefield is a relatively fast process with specialized ships, which is today the most common method. These minelayers can carry several thousand mines and manoeuvre with high precision. The mines are dropped at predefined intervals into the water behind the ship. Each mine is recorded for later clearing, but it is not unusual for these records to be lost together with the ships. Therefore, many countries demand that all mining operations be planned on land and records kept so that the mines can later be recovered more easily.
Other methods to lay minefields include:
- Converted merchant ships – rolled or slid down ramps
- Aircraft – descent to the water is slowed by a parachute
- Submarines – launched from torpedo tubesor deployed from specialized mine racks on the sides of the submarine
- Combat boats – rolled off the side of the boat
- Camouflaged boats – masquerading as fishing boats
- Dropping from the shore – typically smaller, shallow-water mines
- Attack divers – smaller shallow-water mines
In some cases, mines are automatically activated upon contact with the water. In others, a safety lanyard is pulled (one end attached to the rail of a ship, aircraft or torpedo tube) which starts an automatic timer countdown before the arming process is complete. Typically, the automatic safety-arming process takes some minutes to complete. This allows the people laying the mines sufficient time to move out of its activation and blast zones.
Aerial mining in World War II
In the 1930s, Germany had experimented with the laying of mines by aircraft. It became a crucial element in their overall mining strategy. Aircraft had the advantage of speed, and they would never get caught in their own minefields. German mines held a large 450 kg (1,000 lb) explosive charge. From April to June 1940, the Luftwaffe laid 1,000 mines in British waters. Soviet ports were mined, as was the Arctic convoy route to Murmansk. The Heinkel He 115 could carry two medium or one large mine while the Heinkel He 59, Dornier Do 18, Junkers Ju 88 and Heinkel He 111 could carry more.
The USSR was relatively ineffective in its use of naval mines in WWII in comparison with its record in previous wars.
In September 1939, the UK announced the placement of extensive defensive minefields in waters surrounding the Home Islands. Offensive aerial mining operations began in April 1940 when 38 mines were laid at each of these locations: the
As early as 1942, American mining experts such as Naval Ordnance Laboratory scientist Dr. Ellis A. Johnson, CDR USNR, suggested massive aerial mining operations against Japan's "outer zone" (Korea and northern China) as well as the "inner zone", their
A single B-24 dropped three mines into Haiphong harbour in October 1943. One of those mines sank a Japanese freighter. Another B-24 dropped three more mines into the harbour in November, and a second freighter was sunk by a mine. The threat of the remaining mines prevented a convoy of ten ships from entering Haiphong, and six of those ships were sunk by attacks before they reached a safe harbour. The Japanese closed Haiphong to all steel-hulled ships for the remainder of the war after another small ship was sunk by one of the remaining mines, although they may not have realized no more than three mines remained.
Using Grumman TBF Avenger torpedo bombers, the US Navy mounted a direct aerial mining attack on enemy shipping in Palau on 30 March 1944 in concert with simultaneous conventional bombing and strafing attacks. The dropping of 78 mines deterred 32 Japanese ships from escaping Koror harbour, and 23 of those immobilized ships were sunk in a subsequent bombing raid. The combined operation sank or damaged 36 ships. Two Avengers were lost, and their crews were recovered. The mines brought port usage to a halt for 20 days. Japanese mine sweeping was unsuccessful; and the Japanese abandoned Palau as a base when their first ship attempting to traverse the swept channel was damaged by a mine detonation.
In March 1945,
Clearing WWII aerial mines
Between 600,000 and 1,000,000 naval mines of all types were laid in WWII. Advancing military forces worked to clear mines from newly-taken areas, but extensive minefields remained in place after the war. Air-dropped mines had an additional problem for mine sweeping operations: they were not meticulously charted. In Japan, much of the B-29 mine-laying work had been performed at high altitude, with the drifting on the wind of mines carried by parachute adding a randomizing factor to their placement. Generalized danger areas were identified, with only the quantity of mines given in detail. Mines used in Operation Starvation were supposed to be self-sterilizing, but the circuit did not always work. Clearing the mines from Japanese waters took so many years that the task was eventually given to the Japan Maritime Self-Defense Force.
For the purpose of clearing all types of naval mines, the Royal Navy employed German crews and minesweepers from June 1945 to January 1948, organised in the German Mine Sweeping Administration (GMSA), which consisted of 27,000 members of the former Kriegsmarine and 300 vessels. Mine clearing was not always successful: a number of ships were damaged or sunk by mines after the war. Two such examples were the liberty ships Pierre Gibault which was scrapped after hitting a mine in a previously cleared area off the Greek island of Kythira in June 1945, and Nathaniel Bacon which hit a minefield off Civitavecchia, Italy in December 1945, caught fire, was beached, and broke in two.
The damage that may be caused by a mine depends on the "shock factor value", a combination of the initial strength of the explosion and of the distance between the target and the detonation. When taken in reference to ship hull plating, the term "Hull Shock Factor" (HSF) is used, while keel damage is termed "Keel Shock Factor" (KSF). If the explosion is directly underneath the keel, then HSF is equal to KSF, but explosions that are not directly underneath the ship will have a lower value of KSF.
Usually only created by contact mines, direct damage is a hole blown in the ship. Among the crew, fragmentation wounds are the most common form of damage. Flooding typically occurs in one or two main watertight compartments, which can sink smaller ships or disable larger ones. Contact mine damage often occurs at or close to the waterline near the bow, but depending on circumstances a ship could be hit anywhere on its outer hull surface (the USS Samuel B. Roberts mine attack being a good example of a contact mine detonating amidships and underneath the ship).
Bubble jet effect
The bubble jet effect occurs when a mine or torpedo detonates in the water a short distance away from the targeted ship. The explosion creates a bubble in the water, and due to the difference in pressure, the bubble will collapse from the bottom. The bubble is buoyant, and so it rises towards the surface. If the bubble reaches the surface as it collapses, it can create a pillar of water that can go over a hundred meters into the air (a "columnar plume"). If conditions are right and the bubble collapses onto the ship's hull, the damage to the ship can be extremely serious; the collapsing bubble forms a high-energy jet similar to a shaped charge that can break a metre-wide hole straight through the ship, flooding one or more compartments, and is capable of breaking smaller ships apart. The crew in the areas hit by the pillar are usually killed instantly. Other damage is usually limited.
If the mine detonates at a distance from the ship, the change in water pressure causes the ship to resonate. This is frequently the most deadly type of explosion, if it is strong enough.[
The resulting gas cavitation and
Weapons are frequently a few steps ahead of countermeasures, and mines are no exception. In this field the British, with their large seagoing navy, have had the bulk of world experience, and most anti-mine developments, such as
Ships can be designed to be difficult for mines to detect, to avoid detonating them. This is especially true for minesweepers and mine hunters that work in minefields, where a minimal signature outweighs the need for armour and speed. These ships have hulls of glass fibre or wood instead of steel to avoid magnetic signatures. These ships may use special propulsion systems, with
A steel-hulled ship can be
A simpler variation of this technique called wiping, was developed by Charles F. Goodeve which saved time and resources.
Between 1941 and 1943 the US Naval Gun factory (a division of the Naval Ordnance Laboratory) in Washington, D.C., built physical models of all US naval ships. Three kinds of steel were used in shipbuilding: mild steel for bulkheads, a mixture of mild steel and high tensile steel for the hull, and special treatment steel for armor plate. The models were placed within coils which could simulate the Earth's magnetic field at any location. The magnetic signatures were measured with degaussing coils. The objective was to reduce the vertical component of the combination of the Earth's field and the ship's field at the usual depth of German mines. From the measurements, coils were placed and coil currents were determined to minimize the chance of detonation for any ship at any heading at any latitude.
Some ships are built with magnetic inductors, large coils placed along the ship to counter the ship's magnetic field. Using magnetic probes in strategic parts of the ship, the strength of the current in the coils can be adjusted to minimize the total magnetic field. This is a heavy and clumsy solution, suited only to small-to-medium-sized ships. Boats typically lack the generators and space for the solution, while the amount of power needed to overcome the magnetic field of a large ship is impractical.
Active countermeasures are ways to clear a path through a minefield or remove it completely. This is one of the most important tasks of any mine warfare flotilla.
A sweep is either a contact sweep, a wire dragged through the water by one or two ships to cut the mooring wire of floating mines, or a distance sweep that mimics a ship to detonate the mines. The sweeps are dragged by
If a contact sweep hits a mine, the wire of the sweep rubs against the mooring wire until it is cut. Sometimes "cutters", explosive devices to cut the mine's wire, are used to lessen the strain on the sweeping wire. Mines cut free are recorded and collected for research or shot with a deck gun.
Minesweepers protect themselves with an oropesa or paravane instead of a second minesweeper. These are torpedo-shaped towed bodies, similar in shape to a Harvey Torpedo, that are streamed from the sweeping vessel thus keeping the sweep at a determined depth and position. Some large warships were routinely equipped with paravane sweeps near the bows in case they inadvertently sailed into minefields—the mine would be deflected towards the paravane by the wire instead of towards the ship by its wake. More recently, heavy-lift helicopters have dragged minesweeping sleds, as in the 1991 Persian Gulf War.
The distance sweep mimics the sound and magnetism of a ship and is pulled behind the sweeper. It has floating coils and large underwater drums. It is the only sweep effective against bottom mines.
During WWII, RAF Coastal Command used Vickers Wellington bombers Wellington DW.Mk I fitted with degaussing coils to trigger magnetic mines. In a parallel development the Luftwaffe adapted some Junkers 52/3m aircraft to also carry a coil operated by electricity supplied from an onboard generator. The Luftwaffe called this adaption Minensuch (lit. mine-search). In both cases pilots were required to fly at low altitude (up to about 200 feet above the sea) and at fairly low speeds to be effective.
Modern influence mines are designed to discriminate against false inputs and are, therefore, much harder to sweep. They often contain inherent anti-sweeping mechanisms. For example, they may be programmed to respond to the unique noise of a particular ship-type, its associated magnetic signature and the typical pressure displacement of such a vessel. As a result, a mine-sweeper must accurately mimic the required target signature to trigger detonation. The task is complicated by the fact that an influence mine may have one or more of a hundred different potential target signatures programmed into it.
Another anti-sweeping mechanism is a ship-counter in the mine fuze. When enabled, this allows detonation only after the mine fuze has been triggered a pre-set number of times. To further complicate matters, influence mines may be programmed to arm themselves (or disarm automatically—known as self-sterilization) after a pre-set time. During the pre-set arming delay (which could last days or even weeks) the mine would remain dormant and ignore any target stimulus, whether genuine or false.
When influence mines are laid in an ocean minefield, they may have various combinations of fuze settings configured. For example, some mines (with the acoustic sensor enabled) may become active within three hours of being laid, others (with the acoustic and magnetic sensors enabled) may become active after two weeks but have the ship-counter mechanism set to ignore the first two trigger events, and still others in the same minefield (with the magnetic and pressure sensors enabled) may not become armed until three weeks have passed. Groups of mines within this mine-field may have different target signatures which may or may not overlap. The fuzes on influence mines allow many different permutations, which complicates the clearance process.
Mines with ship-counters, arming delays and highly specific target signatures in mine fuzes can falsely convince a belligerent that a particular area is clear of mines or has been swept effectively because a succession of vessels have already passed through safely.
As naval mines have become more sophisticated, and able to discriminate between targets, so they have become more difficult to deal with by conventional sweeping. This has given rise to the practice of mine-hunting. Mine hunting is very different from sweeping, although some minehunters can do both tasks. Minehunting pays little attention to the nature of the mine itself. Nor does the method change much. At the current state of the art, Minehunting remains the best way to deal with influence mines proving to be both safer and more effective than sweeping. Specialized high-frequency sonars and high fidelity sidescaning sonar are used for mine location.: 18 Mines are hunted using sonar, then inspected and destroyed either by divers or ROVs (remote controlled unmanned mini-submarines). It is slow, but also the most reliable way to remove mines. Minehunting started during the Second World War, but it was only after the war that it became truly effective.
Sea mammals (mainly the
French naval officer