Today's mines are designed for deployment against many different classes or types of ships to achieve a variety of results. However, to meet the challenges of the missions that they may be called upon to perform, mines are becoming increasingly complex. Moreover, the number of these mission is so large that no one mine can serve all purposes. And this is why the Navy's stockpile contains many different kinds of mines with the necessary built-in versatilities that provide the options needed for a wide variety of missions. The term sea mines also includes destructors which are general purpose bombs containing influence firing mechanisms. Destructors, however, can be used as land mines as well as sea mines.
In general, some mines, with small explosive charges are designed only for use against river boats and wooden vessels of small displacement. Other mines with large charges can destroy or damage most capital ships. Some mines are intended primarily for use against submarines. Although it has been said that mines are becoming increasingly complex, it is largely because of the intelligence that is built into their firing systems. Conversely, the same technology that made mines more complex in some ways has made them simpler in others. The newer mines, for example, have features which make assembly, testing, and stowing much easier and safer than was possible with older not-so-complex mines. When deployed, mines may be used as offensive or defensive weapons. As offensive weapons, they may be planted in the enemys waterways, harbors, anchorages, and channels or they may be planted in sea lanes removed from the enemys harbor areas to menace his military and commercial shipping. The actual threat of such mines is frequently of equal importance with the actual sinking of ships, since the presence or threat of mines requires the necessary countermeasures to sweep or neutralize them. Consequently, this causes delays in shipping schedules which may require that ships use alternate routes and port areas. As defensive weapons, mines may be planted in ports, harbors, channels, anchorages (perimeter defenses), bays, estuaries, or open waters to protect against enemy offensive seaborne attacks into these areas.Mine warfare began in 1776 when David Bushnell invented the "Bushnell's Keg." This primitive mine was composed of a watertight keg filled with black powder and a flintlock detonator which was suspended from a float. These kegs were placed in the Delaware River so that, it was hoped, they would float into British ships downriver. These early mines were called torpedoes. In fact, when Admiral Farragut said "Damn the torpedoes Captain Drayton, go ahead!" at the Battle of Mobile Bay, he was actually referring to mines; self-propelled torpedoes had not yet been invented.
In 1863, the Confederate Congress established the Torpedo Service, whose mission was to sow Southern waterways with Bushnell's Kegs. These mines were prone to waterlogging and faulty detonators, but they were cheap to produce. Forty-three Federal ships were struck by Confederate mines during the War, twenty-seven of which sank.
During World War I, a 250-mile wide minefield was sown between Scotland and Norway by allied forces to stop German U-boats. This minefield was planted in five months during 1918 by American and British ships, and contained over 72,000 mines.
Modern magnetic, acoustic and pressure-sensitive mines were first developed by the Germans during World War II. Also, the deployment of mines by submarine and aircraft and the development of deep-sea mines sharply increased the need for modern mine countermeasures. Mines were used by all sides throughout World War II, and surface ships were fitted with paravanes to fend off contact mines. In Japan, US aircraft laid more than 12,000 mines around Japanese shipping routes and harbor approaches, sinking 650 ships and choking off all maritime shipping.
It wasnt until World War II that mines were successfully planted by aircraft: and it was then that it became readily apparent that the advantages of air delivery are many. This was demonstrated by the number of notable mining campaigns of that war, the most notable of which was the strategy blockade of the harbors of Japan. in short, airplanes can lay mines suddenly and in great quantity. Moreover, airplanes are the only vehicle capable of replenishing a large mine field without danger from the field itself. Also, planes can lay mines in shallow bodies of water, including rivers and harbors which cannot be transited by submarines or surface minelayers. Although the torpedo was considered the primary weapon of the submarine during World War II, many missions by the Seventh Fleet submarines involved the laying of mines. Throughout the war, submarines had planted 576 mines, resulting in 27 ships sunk and 27 damaged, or one ship per 10 planted mines. During World War II surface craft were used primarily for defensive mining operations, i.e., defending friendly harbors and waters from penetration by enemy vessels. Planting was usually done from specially designed minelayers or from certain other surface craft. Throughout the war, thousands of these mines were laid just outside Chesapeake Bay, around Cape Hatteras, an around Key West to protect our shipping against enemy submarines. Also, large fields were laid in the Atlantic off the coasts of Trinidad and North Africa and in the Mediterranean off the coast of Sicily. Although there is no record of any of the enemys ships being sunk or damaged in the Navys defensive fields, neither is there any record of the enemys ships passing through the fields. Perhaps the knowledge that the fields existed prevented any attempts being made, thus proving the adage that mines work well even when they don't work at all.During the Korean War, American forces were prevented from landing at Wonson for over a week in 1950 until 3,000 Communist mines could be cleared.
In Viet Nam, "destructor" mines, which were made from modified bombs, were widely planted by Viet Cong and North Vietnamese in shallow rivers and deltas to disrupt shipping.
The Persian Gulf War is where the USS GUARDIAN first saw action. Both surface and air mine countermeasures forces were deployed to find and neutralize primitive Iranian mines. Two US Navy combatants were severely damaged - more than $21 million in repairs - by Iraqi mines laid in areas previously thought to be mine free.
A typical bottom mine consists of an explosive case and a firing mechanism. More complicated mines may be outfitted with a variety of other features. A battery may be included in electronic mines; an arming device may be employed to make a mine active only after it has reached a certain depth, a ship counter that allows the mine to let a certain number of valid targets pass before detonating, and a clock delay and sterilizer that make the mine potent only for a certain length of time, after which the mine shuts down. Air-delivered mines may be fitted with a parachute and tail fins to lessen the impact as it strikes the water.
A typical moored mine uses an anchor, which is located on the front of the mine. Upon impact with the bottom of the water, the anchor section breaks away and the rest of the mine rises upwards on a tether cable until it reaches its pre-determined depth. Influence-type mines contain a magnetometer, search coil, hydrophone or pressure-sensitive device that can target specific classes of ships.
Magnetic mines utilize a magnetic search coil or magnetometer to detect passing ships. The older, heavier search coils are used in bottom mines to detect changes in the earth's magnetic field caused by passing vessels. Newer magnetometers are often used in moored mines and can detect ships or submarines in any direction.
Acoustic mines employ a hydrophone to detect the sounds emanated by ships and submarines including engine and propeller noises. Such sounds must meet certain criteria, including frequency band and must increase in volume at a prescribed rate or the mine will ignore them.
Pressure mines use electro-hydraulic pressure sensors to detect ships or submarines. The pressure sensor waits for the pressure drop underwater associated with the passing of a vessel and, if the target vessel is displacing enough water, the mine will actuate.