Naval mine
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A naval mine is a stationary self-contained explosive device placed in water, to destroy ships and/or submarines. Like landmines, they are static weapons deposited and left to wait until they are triggered by the approach of an enemy ship (cf depth charge). They are very cost-effective. Since World War II, mines have damaged or sunk 14 U.S. Navy ships, while air and missile attacks have damaged only four. Naval mines can be used offensively, to hamper enemy shipping and lock it into its harbor, or defensively, to protect friendly shipping and create "safe" zones.
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3.1 Anti sweep mine |
Early History
The English may have used the first naval mines in 1627 at the Siege of La Rochelle, where they launched "floating petards" unsuccessfully against the French navy.
However, an American, David Bushnell invented the first practical mine for use against the British in the American War of Independence. It was a watertight keg filled with gunpowder that was ignited by a percussion lock when it struck a ship.
The American Civil War saw the first successful use of mines, by both sides. The first ship sunk by a mine was the USS Cairo in 1862 in the Yazoo River. Rear Adm. David Farragut's famous quote, Damn the torpedoes, full speed ahead! refers to a minefield laid at Mobile, Ala.
In the 19th century, mines were called torpedoes, a name likely conferred by Robert Fulton after a fish that gives powerful electric shocks. A spar torpedo was a mine attached to a long pole and detonated when the ship carrying it rammed another one. CSS Hunley used one to sink USS Housatonic on Feb. 17, 1864. A Harvey Torpedo was a type of floating mine towed alongside a ship, and was briefly in service in the Royal Navy in the 1870s. Other "torpedoes" attached to ships or even launched under their own power. One such weapon, called the Whitehead Torpedo after its inventor, eventually drew the appellation from static devices to self-propelled underwater missiles.
The mine's next major use came in the Russo-Japanese War in 1904, where the Russian battleship Petropavlovsk was sunk, killing the fleet commander, Admiral Makaroff, and most of the crew. On the other side, two Japanese battleships sunk on Russian mines just on one day.
Many of the early mines were extremely fragile and dangerous to handle, with glass containers filled with nitroglycerine or mechanical devices that activated them upon tipping. Several minelaying ships were destroyed when their cargo exploded.
Types
Naval mines may be classified into two major groups.
Contact mines
The earliest mines were usually of this type. They are still used today as they are extremely cheap compared to any other anti-ship weapon and still very effective both as a terror weapon and to sink enemy ships. Contact mines have to be very close to the enemy before they detonate, which limits the damage (read below section on damage for explanation).
Early mines had mechanical mechanisms to detonate them, but these were superseded in the 1870s by the Hertz 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 protruberances, each containing a glass vial filled with sulphuric 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 contains no acid electrolyte. This energizes the battery, which detonates the explosive.
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During World War I, the British heavily mined the English Channel and later large areas of the North Sea to prevent German submarines from using it. As the submarine could be at any depth down to the seabed, an American invention, the antenna mine, was widely used. This had a copper wire attached to a buoy that floated above the mine. The top part of the cable connecting the buoy to the weight on the seabed was also made of copper. The copper wire was insulated from the steel cable below it. If a submarine's steel hull touched the copper wire, the slight voltage produced because of the contact between two dissimilar metals was amplified and detonated the explosive.
Limpet mines
Limpet mines are a special form of contact mine which are attached to the target by magnets and left. The process of attaching them is usually carried out by a swimmer or diver. They are set off by a time fuse. Normally they are directly attached, but the warhead of the human torpedo was linked to the magnets by wires about one foot (30 cm) long.
Typically they have special compartments within them to ensure that the mine has only a slight negative buoyancy making them easier to handle.
An example of the use of limpet mines by British special forces was in Operation Frankton which had the objective of disabling and sinking merchant shipping moored at Bordeaux, France in 1942. The operation was also the subject of a feature film titled The Cockleshell Heroes.
Another well known use was the sinking of Rainbow Warrior by the French secret service in Auckland harbour, New Zealand, on July 10 1985. This was a standard covert use of mines, but also a deeply flawed operation.
Floating contact mines
The original mine type floats anywhere from just below the surface of the water to several hundred meters down. A cable connecting the mine to an anchor on the seabed prevents them from drifting away. The explosive and detonating mechanism is contained in a metal or plastic shell, which also has considerable buoyancy. 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. This is useful to avoid having a "less valuable" ship detonate the mines.
These mines usually have a weight of 200 kg, including 80 kg of explosives (TNT).
Drifting contact mines
Drifting mines were occasionally used during World War I and World War II. However, they were more feared than effective. A drifting mine is simply a floating mine without any mooring. Sometimes floating mines rip their moorings and become drifting mines, but modern mines should be constructed to deactivate themselves if this happens. However, after several years at sea, the deactivation mechanism might not function as intended and the mines may remain active. 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 that the Germans either were leaving floating mines in their wake, or were drawing him towards submarines. Both dangers were imaginary - the German fleet did not carry any mines.
Churchill promoted "Operation 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 fixed interval by which time they should have reached German territory.
After World War I, the drifting contact mine was banned, even if it was occasionally used during World War II. The drifting mines were much harder to remove after the war and they caused about as much damage to both sides.
These mines usually weight 120 kg, including 80 kg of explosives (TNT)
Bottom contact mines
A bottom contact mine is the simplest form of mine imaginable. It is just a collection of explosive and a trigger lying on the bottom. They have been used against submarines, as submarines sometimes lie on the bottom to lower their acoustic signature. They are also used to prevent landing crafts from reaching the shore and were a major obstacle during the landings on the D-Day. The Germans used antitank mines here with minor modifications to make them more reliable underwater. They attached the mines to the front end of many of the obstacles seen in photos of the landing.
These mines usually weight 2-50 kg, including 1-40 kg of explosives (TNT or hexatonal).
Distance mines
Distance mines do not need physical contact with the ship to detonate. The earliest ones were moored mines used in the American Civil war and detonated electrically by observers on the shore. These were seen as superior to contact mines because they only deprived the waterway to the enemy. Distance mines use several kinds of instruments to detect if an enemy is nearby, most frequently a combination of acoustic, magnetic and pressure sensors. More exotic solutions also exist, such as optical shadows or electro potential sensors. These are modern mines and frequently cost many times more than contact mines. Still, they are very cheap compared to other anti-ship weapons and can be deployed in large numbers.
Remotely controlled mines
Frequently used in combination with coastal artillery and hydrophones the remote controlled mines can be in place even in peacetime, which is a huge advantage when it comes to blocking important shipping routes to defend harbours. The mines are usually modified distance mines and can be turned into "normal" mines with a switch (which prevents the enemy from simply capturing the controlling station and deactivating the mines), detonated by hand or be allowed to detonate on their own.
These mines usually weight 200 kg, including 80 kg of explosives (TNT or hexatonal).
Floating distance mines
The floating distance mine is the backbone of any mine system today. They are deployed everywhere the water is too deep for bottom distance mines. Usually equipped with magnetic or acoustic sensors, a floating distance mine is effective against most kinds of ships. A floating distance mine usually has a lifetime of more than 10 years, some of them almost unlimited. The floating mines are limited by the fact that they have to float, so they cannot carry unlimited amount of explosives. More than 150 kg is simply a waste of money, as the mine gets too large to handle and the extra explosives do not add much to the mine's effectiveness.
These mines usually weight 200 kg, including 80 kg of explosives (hexatonal)
Bottom distance mines
Bottom distance mines are used when the water is no more than 60 meters deep or when mining for submarines down to around 200 meters. They are much harder to detect and clear, and they can carry a much larger payload than a floating mine. Bottom mines also use pressure sensitive instruments, which are less sensitive to sweeping than any other type.
These mines usually weight 150-1500kg, including 125-1400kg of explosives (hexatonal)
Unusual mine systems
There have been several specialized mines developed for other purpose and functions than the common minefield.
Anti sweep mine
The anti sweep mine is a very small mine (40 kg warhead) with as small a floating device as possible. When the wire of a mine sweep hits the mine, it "sinks", letting the sweep wire drag along the anchoring wire of the mine until the sweep hits the mine. 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 harder.
Rocket mine
Originally a Russian invention the rocket mine is a bottom distance mine that fires a homing rocket (not torpedo) upwards towards the target. It is intended to allow a bottom mine to attack surface ships from a greater depth.
Torpedo mine
The torpedo mine is simply a torpedo placed on the bottom with a system to fire it when an enemy is nearby. It has good range, but is sensitive to anti torpedo system, such as screens.
Bouquet mine
The bouquet mine is a single anchor attached to several floating mines. It is designed so that when one mine is swept/detonates another takes its place. It is a very sensitive construction and might not always work.
Ascending mine
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.
Homing mine
The homing mine is a floating distance mine with a small engine that lets it move closer to its intended target before it detonates.
Active mine
An active mine is a mine that moves on its own when it is deployed. Usually submarines deploy active mines and they have the form of a torpedo. That way the mine can be deployed deep inside an enemy harbour.
Mine laying
Laying a minefield goes very fast with specialized ships, which is still today the most common method. These minelayers can carry several thousand mines and manoeuvre with high precision. The mines are dropped at a predefined interval into the water behind the ship. Each mine is recorded for later clearing, but it is not unusual for these recordings to be lost together with the ships. Therefore many countries demand that all mining operations shall be planned on land and records kept so the mines can later be recovered more easily.
Other methods to lay minefields includes:
- Converted merchant ships
- Airplanes
- Submarines
- Combat boats
- Camouflaged boats
- Dropping from the shore
- Attack divers
Most mines are automatically activated when in the water, after a safety has been removed, and can both safely and easily be delivered in almost any method imaginable.
Damage
The damage of a mine depends on the distance from the detonation, and is not always less because the detonation is some distance away.
Direct damage
Usually only created by contact mines, direct damage is simply a hole blown in a part of the ship. Among the crew, shrapnel wounds are most common. This rarely sinks the ship, but might flood one or two compartments - usually in the bow (which is the area where the enlisted traditionally sleeps and explains why enlisted are far more likely to die in a mine detonation than officers.)
Bubble jet effect
If the mine detonates in the water some distance from the ship, the bubble jet effect happens. The explosion creates a "hole" in the water, and due to the difference in pressure, this sphere will collapse from the bottom. This creates the famous "pillar" of water that can go well over a hundred meters into the air. The damage to the ship is heavy. The water breaks a meter wide hole straight through the ship that floods one or more compartments. The structural damage might break the ship apart. The crew in the areas hit by the water pillar are usually killed instantly. Other damage is usually limited.
The shaking effect
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 strong enough. The whole ship is roughly shaken, and everything, bolted down or not, is tossed around. Engines rip free from their beds, cables from their holders, etc. A badly shaken ship usually sinks quickly, with hundreds, or thousands of small leaks all over the ship and no way to power the pumps. The crew fare no better, as the violent shaking tosses them around. One of the most common wounds is broken femur, close to the hip. The reason for this is the violent upward motion of the ship. To counter this, minesweeper crews are ordered to walk and stand with their knees slightly bent at all time – the "minesweeper walk".
Countermeasures
Weapons are frequently a few steps ahead of countermeasures and mines are no exception. Currently, with modern mine hunting, countermeasures are beginning to catch up. However, the next generation of rocket mines may very well change that.
Passive countermeasures
By building ships with as low signature as possible you can avoid detonating mines. This is especially true for minesweepers and mine hunters that have to work inside minefields. These ships are built out of glass fibre or even wood instead of steel to avoid magnetic signatures, they use special engines to limit the acoustic signatures and they are made with hulls that produce a low pressure signature. Of course, these measures create other problems. The ships are expensive, slow and vulnerable to enemy fire. Therefore, they need protection. Many modern ships have a mine warning sonar — simple sonar looking forward and warning the crew if it spots something that might be a mine in the water before the ship. It is only effective when moving slowly.
A ship can be degaussed using a special degaussing station that contains many large coils and induces a magnetic field in the hull. This is a rather problematic solution however, as the navigational equipment needs recalibration afterwards and everything made of metal has to be kept in exactly the same place. Ships slowly regain their magnetic field as they adjust to the earth’s magnetic field, so the process has to be repeated every six months.
Active countermeasures
The active countermeasures are the ways to clear a path through a minefield (or to remove it completely.) This is one of the most important tasks of any mine warfare flotilla.
Mine sweeping
A sweep is either a contact sweep, a simple metal wire dragged through the water by one or two ships to cut the mooring wire of floating mines, or a distance sweep that tries to mimic a ship to get the mines to detonate. The sweeps are dragged by minesweepers, either military ships or converted trawlers. Each run covers between one and two hundred meters, and the ships have to move slowly in a straight line, which makes them very vulnerable to enemy fire. This was most famously exploited by the Turkish army in the Dardanelles in 1915, when mobile howitzer batteries prevented the British and French from clearing a way through the minefields.
If a contact sweep hits a mine, the wire of the sweep (which is made of high quality steel) rubs against the wire mooring the mine until it is cut. Sometimes "cutters", explosive devices to cut the mine's wire, are used to lessen the strain on the sweeping wire. Any mine cut free is recorded and either collected for research or simply shot with the deck cannon.
Minesweepers can protect themselves by using a paravane instead of a second minesweeper. A paravane is a torpedo-shaped float similar in shape to a Harvey Torpedo and is pulled away from the ship towing it. 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.
The distance sweep tries to mimic 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.
Modern distance mines are much more sensitive and much harder to sweep. They often contain anti-sweeping mechanisms such as sensitivity only to the noise of certain types of ship or will detonate only after their mechanism has been triggered a specified number of times. They may also only arm themselves (or disarm automatically - known as self-sterilization) after a set time.
Mine hunting
Mine hunting is very different from sweeping, even if the same ships do both tasks. When mine hunting, the mines are located using sonar, then destroyed either by divers or ROV (remote controlled unmanned mini submarines). It is slow, but also the most secure way to remove mines. Mine hunting started during the Second World War, but it was only after the war that it became a truly effective method.
Mine breaking
A more drastic method is simply to take a cargo ship, load it with cargo that makes her less vulnerable to sinking (wood for example) and drive her through the minefield, letting the ship that should be protected follow the same path. This technique has been used several times during war, not always successfully.
Strategy
Mines are used in many different ways and for different reasons. International law requires nations to declare when they mine an area. This is to make it easier for civil shipping to avoid the mines. The warnings do not have to be specific however. For example, Britain declared areas such as the English Channel, North Sea and French coast mined during the Second World War.
There are three main uses of mines: Offensive, Defensive and Psychological. Offensive mines are placed in enemy waters, outside harbours and in important routes. Their target is both civilian and military ships, and they are used as much to sink ships as to stop the important sea transports. Defensive minefields protect a coast from enemy ships and submarines, and force them into areas that are easier to defend. Psychological minefields are usually placed in trade routes, and are used to stop shipping to the enemy nation. They are also spread out thinly, to create a feeling of random minefields in large areas. A single mine in a route can stop shipping for days until the entire area is swept.
Minefields can be placed by traditional minelayers, large ships carrying thousands of mines, smaller costal ships, submarines, airplanes and even by just dropping them into a harbour by hand.
Economy
Just like mine warfare on land the economical burden in mine warfare at sea is very uneven. The cost of producing and laying a mine is usually between 1/10th and 1/200th of the cost to remove said mine. The time aspects are also critical, as it can take up to 200 times the time to clear a minefield than to lay it. Using different methods to make clearing harder can increase this time. Even today parts of minefields left since the second world war remain, as they are simply too spread out and expensive to clear. Also many of these mines are no longer active, even if contact mines theoretically can be active for hundreds of years.
A simple contact mine can cost as little as $200. A simple distance mine around $300. This makes them very attractive weapons in uneven conflicts, as they can deny access for expensive ships to large areas for a long time, without risking friendly losses.
Mines and the USA
Modern usage of mines against and by the USA
During the Iran-Iraq War from 1980 to 1988, several areas of the Persian Gulf and nearby waters were mined by each side. On April 14, 1988, the USS Samuel B. Roberts (FFG-58) struck an M-08/39 mine in the central Gulf shipping lane, wounding 10 sailors.
During the Gulf War, Iraqi naval mines severely damaged USS Princeton (CG-59) and USS Tripoli (LPH-10).
US Mines
The United States Navy MK56 ASW mine (the oldest still in use by the US) was developed in 1966. Since that time, more advances in technology have given way to the development of the MK60 CAPTOR (short for "encapsulated torpedo"), the MK62 and MK63 Quickstrike and the MK67 SLMM (Submarine Launched Mobile Mine). Most mines in the USN's arsenal today are delivered by aircraft to target.
MK67 SLMM Submarine Launched Mobile Mine
The SLMM was developed by the United States as a submarine deployed mine for use in areas inaccessible for other mine deployment techniques or for covert mining of hostile environments. The SLMM is a shallow water mine and is basically a modified MK37 torpedo.
General Characteristics
- Type: Submarine laid bottom mine
- Detection System: Magnetic/seismic or Magnetic/seismic/pressure target detection devices (TDDs)
- Dimensions: 485 mm by 4.09 m (19 by 161 in)
- Depth Range: Shallow water
- Weight: 754 kg (1658 lb)
- Explosives: 230 kg (510 lb) high explosive
- Date Deployed: 1987
MK65 Quickstrike
The Quickstrike is a family of shallow-water aircraft-laid mines used by the United States, primarily against surface craft. The MK65 is a 2,000 lb (900 kg) mine. Other Quickstrike versions (MK62, MK63, and MK64) are converted 500 lb (230 kg) and 1000 lb (450 kg) general-purpose bombs.
General Characteristics
- Type: aircraft-laid bottom mine
- Detection System: Magnetic/seismic/pressure target detection devices (TDDs)
- Dimensions: 740 mm by 3.25 m (29 by 128 in)
- Depth Range: Shallow water
- Weight: 1086 kg (2390 lb)
- Explosives: Various loads
- Date Deployed: 1983
MK60 CAPTOR
The CAPTOR is the United States Navy's primary anti-submarine weapon. This deep-water mine is laid by aircraft or submarine, and is anchored to the ocean floor. Upon detection of a hostile submarine, the CAPTOR launches a MK46 Mod 4 torpedo.
General Characteristics
- Type: Aircraft, ship or submarine laid magnetically moored mine
- Detection System: Reliable acoustic path (RAP) sound propagation
- Dimensions:
- Aircraft or Ship laid: 530 mm by 3.68 m (21 by 145 in)
- Submarine laid: 530 mm by 3.35 m (21 by 132 in)
- Depth Range: Deep water
- Weight:
- Air or Ship laid: 1077 kg (2370 lb)
- Submarine laid: 935 kg (2056 lb)
- Explosives: 44 kg (96 lb) of PBXN-103 high explosive in a MK46 torpedo
- Date Deployed: 1979
MK56
General Characteristics
- Type: Aircraft laid moored mine
- Detection System: Total field magnetic exploder
- Dimensions: 570 mm by 2.9 m (22.4 by 114.3 in)
- Depth Range: Moderate depths
- Weight: 909 kg (2000 lb)
- Explosives: 164 kg (360 lb) HBX-3
- Date Deployed: 1966
References
- Weapons That Wait. Gregory K. Hartmann with Scott C. Truver. Annapolis: Naval Institute Press, 1991.da:sømine