Thursday, March 10, 2011

Naval mine (or sea mine)

A naval mine is a self-contained explosive device placed in water to destroy surface ships or submarines. Unlike depth charges, mines are deposited and left to wait until they are triggered by the approach of, or contact with, an enemy vessel. Naval mines can be used offensively—to hamper enemy shipping movements or lock vessels into a harbour; or defensively—to protect friendly vessels and create "safe" zones.

Polish wz. 08/39 contact mine. The protuberances around the top of the mine, called Hertz horns, are part of the detonation mechanism.

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$1000, 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 anywhere from 0.5% to 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. It is possible for some of these 1940s-era mines to remain dangerous for many years to come.

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 with the aim of sinking 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.

In 1988, an Iranian M-08 mine made a 25-foot (8 m) hole in the hull of the USS Samuel B. Roberts (FFG-58), forcing the ship to seek temporary repairs in a dry dock in Dubai, UAE.

Minefields designed for psychological effect are usually placed on trade routes and are used to stop shipping reaching an enemy nation. They are often spread thin, 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.

International law requires nations to declare when they mine an area, in order to make it easier for civil shipping to avoid the mines. The warnings do not have to be specific; during World War II, Britain declared simply that it had mined the English Channel, North Sea, and French coast.

The precursor to naval mines was first described by the early Ming Dynasty Chinese artillery officer Jiao Yu, in his 14th century military treatise known as the Huolongjing. Chinese records tell of naval explosives in the 16th century, used to fight against Japanese pirates (Wokou). This kind of naval mine was loaded in a wooden box, sealed by putty. General Qi Jiguang made several timed, drifting explosives to harass Japanese pirate ships. However, in the Tiangong Kaiwu ('The Exploitation of the Works of Nature') treatise, written by Song Yingxing in 1637 AD, it describes naval mines with a rip cord pulled by a hidden ambusher located on the nearby shore which rotated a steel wheellock flint mechanism to produce sparks and ignite the fuse of the naval mine. Although this is the rotating steel wheellock's first use with naval mines, Jiao Yu had described their use for land mines back in the 14th century.

The first plan for a sea mine in the West was by Ralph Rabbards, who presented his design to Queen Elizabeth I of England in 1574. The Dutch inventor Cornelius Drebbel was employed in the Office of Ordnance by King Charles I of England to make weapons, including a "floating petard" which proved a failure. Weapons of this type were apparently tried by the English at the Siege of La Rochelle in 1627.

Closeup of the Roberts' damaged hull.

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 floated toward the enemy, detonated by a sparking mechanism if it struck a ship.

In 1812 Russian engineer Pavel Shilling exploded an underwater mine using an electrical circuit. In 1854, during the unsuccessful attempt of the Anglo-French fleet to seize Kronshtadt fortress, British steamships HMS Merlin (9 June 1855, the first successful mining in history), HMS Vulture and HMS Firefly were damaged by underwater explosions of Russian naval mines. More than 1500 naval mines, or infernal machines, designed by Moritz von Jacobi and Alfred Nobel were set by Russian naval specialists in the Gulf of Finland during the Crimean War. The mining of Vulcan led to the worlds first minesweeping operation during the next 72 hours, 33 mines were swept.

The American Civil War also saw the successful use of mines. The first ship sunk by a mine was the USS Cairo in 1862 in the Yazoo River. Rear Admiral David Farragut's famous statement, "Damn the torpedoes, full speed ahead!" refers to a minefield laid at Mobile, Alabama.

In the 19th century, mines were called torpedoes, a name probably conferred by Dennis Fletcher after the torpedo fish, which 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. The H. L. Hunley used one to sink the USS Housatonic on February 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 propelled themselves. One such weapon, called the Whitehead torpedo after its inventor, caused the word "torpedo" to be used for self-propelled underwater missiles rather than static devices.

During the Boxer Rebellion, Imperial Chinese forces deployed a weapon called "electric mines" on June 15, at the river Beihe (Peiho) before the Battle of Dagu Forts (1900), to prevent the western Eight-Nation Alliance from sending ships to attack. This was reported by American military intelligence in the United States. War Dept. by the United States. Adjutant-General's Office. Military Information Division.

The next major use of mines was during the Russo-Japanese War of 1904-1905. They proved their worth as weapons in this conflict. For instance, two mines blew up when the Russian battleship Petropavlovsk struck them near Port Arthur, sending the holed vessel to the bottom and killing the fleet commander, Admiral Stepan Makarov, and most of her crew in the process. The toll inflicted by mines was not confined to the Russians, however. The Japanese Navy lost two battleships, four cruisers, two destroyers and a torpedo-boat to offensively laid mines during the war. Most famously, in May 1905, the Russian minelayer Amur planted a minefield off Port Arthur and succeeded in sinking the Japanese battleship Hatsuse.

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 at the turn of the century, submarine mines played a major role in the defense of U.S. harbors against enemy attack. The mines employed were controlled mines, anchored to the bottoms of the harbors and detonated under control from large mine casemates on shore.

Explosion of a naval mine during World War II.

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 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.

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 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 hole ships’ hulls. By the beginning of World War II, most nations had developed mines that could be dropped from aircraft and floated on the surface, making it possible to lay them in enemy harbors. The use of dredging and nets was effective against this type of mine, but this consumed time and resources, and required harbors 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 magnetically and detonating at a distance, causing damage with the shock wave of the explosion. Ships that had successfully run the gauntlet of the Atlantic crossing were sometimes destroyed entering freshly cleared British harbors. More shipping was being lost than could be replaced, and Churchill ordered the intact recovery of one of these new mines was of the highest priority.

The British experienced a stroke of luck in November 1939. A German mine was dropped from an aircraft onto the mud flats of the Thames estuary during low tide. As if this was not sufficiently good fortune, the land belonged to the army, and a base with men and workshops was at hand. Experts were dispatched from London to investigate the mine. They had some idea that the mines used magnetic sensors, so everyone removed all metal, including their buttons, and made tools of non-magnetic brass. They disarmed the mine and rushed it to labs at Portsmouth, where scientists discovered a new type of arming mechanism. A large ferrous object passing through the Earth's magnetic field will concentrate the field through it; the mine's detector was designed to trigger at the mid-point of a steel-hulled ship passing overhead. The mechanism had an adjustable sensitivity, calibrated in milligauss. (As it turned out, the German firing mechanism was overly sensitive, making sweeping easier.) The U.S. began adding delay counters to their magnetic mines in June 1945.

From these data, methods were developed to clear the 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 induced 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. Wartime Japanese sweep methods, by contrast, never advanced much past 1930s standards, and failed entirely to keep up with new American mines, clearing no more than 15% of all the mines laid in Japan's coastal waters. Moreover, IJN's minesweeping force was derisively small, only 350 ships, numbering 20,000 men.

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.

A CAPTOR mine being loaded onto a B-52 bomber.

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, which were used as troopships. This was felt to be impracticable for the myriad of smaller warships and merchant vessels, not least due to the amount of copper that would be required. It was found that "wiping" a current-carrying cable up and down a ship' 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. Many of the boats that sailed to Dunkirk were degaussed in a marathon four day effort by degaussing stations.

The Allies deployed acoustic mines, against which even wooden-hulled ships (in particular minesweepers) remained vulnerable. Japan developed sonic generators to sweep these; the gear was not ready by war's end. The primary method Japan used was small air-delivered bombs. This was profligate and ineffectual; used against acoustic mines at Penang, she needed 200 bombs to detonate just 13 mines.

The Germans had also 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. Japan's antiquated sweep methods, lifting mines in nets, accidentally proved useful against these mines; it remained too slow and hazardous to be truly effective, especially in light of the high numbers being laid.

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%.

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 damaged 11 U.S. naval vessels.

During the Iran–Iraq War from 1980 to 1988, the belligerents mined several areas of the Persian Gulf and nearby waters. On April 14, 1988, the USS Samuel B. Roberts (FFG-58) struck an Iranian M-08/39 mine in the central Persian Gulf shipping lane, wounding 10 sailors.

In the summer of 1984, magnetic sea mines damaged at least 19 ships in the Red Sea. The US concluded that Libya was probably responsible for the minelaying. In response the US, Britain, and France launched Operation Intense Look, a minesweeping operation, in the Red Sea.

On the orders of the Reagan administration, the CIA mined Nicaragua's Sandino port in 1984 in support of the Contra guerrilla group. A Soviet tanker was among the ships damaged by these mines. In 1986, in the case of Nicaragua v. United States, the International Court of Justice ruled that this mining was a violation of international law.

During the Gulf War, Iraqi naval mines severely damaged USS Princeton (CG-59) and USS Tripoli (LPH-10).

Types of Naval mines: 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 two major groups.

The earliest mines were usually of the contact mine 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 terror weapon and 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 single 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 contains no acid electrolyte. This energizes the battery, which detonates the explosive.

Earlier forms of the detonator used a vial filled with 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 British 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 and detonated the explosives.

Limpet mines are a special form of contact mine which are attached to the target by magnets and left, and are so named because of the superficial similarity to the limpet, a mollusk.

Generally, moored contact mines type 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 littoral waters it is important to ensure that the mine does not become visible when the sea level falls at low tide, so the preset cable length is adjusted to take account of tides. Even at the time of the Second World War there were mines which could be moored in 300-metre-deep water.

Floating mines typically have a mass of around 200 kg, including 80 kg of explosives e.g. TNT, minol or amatol.
A German contact mine laid in Australian waters during World War II.

During WWII mine traps were used for blocking port entrances. Two floating mines were anchored some distance apart on either side of a shipping channel, linked by a chain. When a deep draft vessel passed through the trap it would pull the chain along with it, dragging the mines onto the sides of the ship; the resulting double explosion often sank it. This system was not used extensively, but proved effective in blocking ports.

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.

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.

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.

A bottom contact mine is the simplest form of mine. It is merely an explosive charge with some form of fuze fitted lying on the seafloor. They have been used against submarines, as submarines sometimes lie on the seafloor to reduce their acoustic signature. They are also used to prevent landing craft from reaching the shore and were a major obstacle during the D-Day landings. The Germans used antitank mines here with minor modifications to make them more reliable underwater, attaching the mines to the front of many of the obstacles seen in photos of the landing.

German World War II magnetic mine that landed on the ground instead of the water.

These mines usually weighed 2 to 50 kg, including 1 to 40 kg of explosives (TNT or hexatonal).

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.

Modern examples usually weigh 200 kg (440 lb), including 80 kg (175 lb) of explosives (TNT or hexatonal).

Influence mines are triggered by the influence of a ship or submarine, rather than direct contact. Such mines incorporate electronic sensors designed to detect the presence of a vessel and detonate when it comes within the blast range of the warhead. The fuzes on such mines may incorporate one or more of the following sensors: magnetic, passive acoustic or water pressure displacement caused by the proximity of a vessel.

Infernal machines in the Potomac River in 1861 during the American Civil War, sketch by Alfred Waud.

First used during the First World War, their use became more general in the Second World War. The sophistication of influence mine fuzes has increased considerably over the years as first transistors and then microprocessors have been incorporated into designs. Simple magnetic sensors have been superseded by total-field magnetometers. Whereas early magnetic mine fuzes would respond only to changes in a single component of a target vessel's magnetic field, a total field magnetometer responds to changes in the magnitude of the total background field (thus enabling it to better detect even degaussed ships). Similarly, the original broadband hydrophones of 1940s acoustic mines (which operate on the integrated volume of all frequencies) have been replaced by narrow-band sensors which are much more sensitive and selective. Mines can now be programmed to listen for highly specific acoustic signatures (e.g. a gas turbine powerplant and/or cavitation sounds from a particular design of propellor) and ignore all others. The sophistication of modern electronic mine fuzes incorporating these Digital Signal Processing capabilities makes it much more difficult to detonate the mine with electronic countermeasures because several sensors working together (e.g. magnetic, passive acoustic and water pressure) allow it to ignore signals which are not recognised as being the unique signature of an intended target vessel.

Modern influence mines such as the BAE Stonefish are computerised, with all the programmability that this implies e.g. the ability to quickly load new acoustic signatures into fuzes, or program them to detect a single, highly distinctive target signature. In this way, a mine with a passive acoustic fuze can be programmed to ignore all friendly vessels and small enemy vessels, only detonating when a very large enemy target passes over it. Alternatively, the mine can be programmed specifically to ignore all surface vessels regardless of size and exclusively target submarines.

Even as far back as the Second World War it was possible to incorporate a "ship counter" facility into mine fuzes e.g. set the mine to ignore the first two ships to pass over it (which could be mine-sweepers deliberately trying to trigger mines) but detonate when the third ship passes overhead—which could be a high-value target such as an aircraft carrier or oil tanker. Even though modern mines are generally powered by a long life lithium battery, it is important to conserve power because they may need to remain active for months or even years. For this reason, most influence mines are designed to remain in a semi-dormant state until an unpowered (e.g. deflection of a mu-metal needle) or low-powered sensor detects the possible presence of a vessel, at which point the mine fuze powers up fully and the passive acoustic sensors will begin to operate for some minutes. It is possible to program computerised mines to delay activation for days or weeks after being laid; similarly, they can be programmed to self-destruct or render themselves safe after a preset period of time, e.g., 12 days or 12 months. Generally, the more sophisticated the mine design, the more likely it is to have some form of anti-handling device fitted in order to hinder clearance by divers or remotely piloted submersibles.

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 area denial or "channelizing" weapons. Moored mines usually have lifetimes of more than 10 years, and some almost unlimited. These mines usually weigh 200 kg (440 lb), including 80 kg (175 lb) of explosives (hexatonal). In excess of 150 kg (330 lb) of explosives the mine becomes inefficient, as it becomes too large to handle and the extra explosives add little to the mine's effectiveness.

Bottom mines are used when the water is no more than 60 meters (180 ft) deep or when mining for submarines down to around 200 meters (660 ft). They are much harder to detect and sweep, and can carry a much larger warhead than a moored mine. Bottom mines commonly use pressure sensitive exploders, which are less sensitive to sweeping.

These mines usually weigh between 150 and 1,500 kilograms (330 to 3,300 pounds), including between 125 and 1,400 kg (275 to 3,090 pounds) of explosives.

David Bushnell's mines destroying a British ship in 1777.

The torpedo mine is a self-propelled variety, able to lie in wait for a target and then pursue it e.g. the CAPTOR mine. Other designs such as the Mk 67 Submarine Launched Mobile Mine (which is based on a Mark 37 torpedo) are capable of swimming as far as 10 miles through or into a channel, harbor, 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. Generally, torpedo mines incorporate computerised acoustic and magnetic fuzes.

The U.S. Mark 24 "mine", code-named FIDO, was actually an ASW homing torpedo. The mine designation was disinformation to conceal its function.

During the Cold War a number of tests were conducted with naval mines fitted with tactical nuclear warheads. These weapons were experimental and never went into production.

Daisy-chained mine. 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 60 feet (18 m) away from its neighbour, and each floats a few metres 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 the Second World War.

Dummy mine. 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.


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, shrapnel 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).

The bubble jet effect occurs when a mine detonates in the water a short distance away from the 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 that can break a meter 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.

The Baengnyeong incident, in which the ROKS Cheonan broke in half and sank off the coast South Korea in 2010, is thought by some to have been caused by the bubble jet 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 it is strong enough. The whole ship is dangerously shaken and everything onboard is tossed around. Engines rip from their beds, cables from their holders, etc. A badly shaken ship usually sinks quickly, with hundreds, or even 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. This shaking is powerful enough to cause disabling injury to knees and other joints in the body, particularly if the affected person stands on surfaces connected directly to the hull (such as steel decks).

The resulting gas cavitation and shock-front-differential over the width of the human body is sufficient to stun or kill divers.


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