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A land mine is an explosive device concealed under or on the ground and designed to destroy or disable enemy targets, ranging from combatants to vehicles and tanks, as they pass over or near it. Such a device is typically detonated automatically by way of pressure when a target steps on it or drives over it, although other detonation mechanisms are also sometimes used. A land mine may cause damage by direct blast effect, by fragments that are thrown by the blast, or by both.
The history of land mines can be divided up into three main phases: In the ancient world, buried spikes provided many of the same functions as modern mines. Mines using gunpowder as the explosive were used from the Ming Dynasty to the American Civil War. Subsequently, high explosives were developed and used in land mines.
A more easily deployed defense used by the Romans was the caltrop, a weapon about 12–15 cm across with four sharp spikes that are oriented so that when it is thrown on the ground, one spike always points up. As with modern antipersonnel mines, caltrops are designed to disable soldiers rather than kill them, and they also stop mounted forces. They were used by the Jin Dynasty in China at the Battle of Zhongdu to slow down the advance of Genghis Khan's army; Joan of Arc was wounded by one in the Siege of Orleans; in Japan they are known as tetsu-bishu and were used by ninjas from the fourteenth century onwards. Caltrops are still strung together and used as roadblocks in some modern conflicts.
A 14th-century military treatise, the Huolongjing (Fire Dragon Manual), describes hollow cast iron cannonball shells filled with gunpowder. The wad of the mine was made of hard wood, carrying three different fuses in case of defective connection to the touch hole. These fuses were long and lit by hand, so they required carefully timed calculation of enemy movements.
At Augsburg in 1573, three centuries after the Chinese invented the first pressure-operated mine, a German military engineer by the name of Samuel Zimmermann invented the Fladdermine (flying mine). It consisted of a few pounds of black powder buried near the surface and was activated by stepping on it or tripping a wire that made a flintlock fire. Such mines were deployed on the slope in front of a fort. They were used during the Franco-Prussian War but were probably not very effective because a flintlock does not work for long when left untended.
Victim-activated mines were also unreliable because they relied on a flintlock to ignite the explosive. The percussion cap, developed in the early 19th century, made them much more reliable, and pressure-operated mines were deployed on land and sea in the Crimean War (1853–1856).
In 1847, Ascanio Sobrero invented nitroglycerine to treat angina pectoris and it turned out to be a much more powerful explosive than guncotton. It was very dangerous to use until Alfred Nobel found a way to incorporate it in a solid mixture called dynamite and developed a safe detonator. Even then, dynamite needed to be stored carefully or it could form crystals that detonated easily. Thus, the military still preferred guncotton.
In their colonial conflicts, the British had few scruples about using mines than the Americans had in the Civil War. They used them in the Siege of Khartoum to hold off a much larger Sudanese Mahdist force for ten months. In the end, however, the town was taken and the British massacred. In the Boer War (1899–1903), they succeeded in holding Mafeking against Boer forces with the help of a mixture of real and fake minefields; and they laid mines alongside railroad tracks to discourage sabotage.
Towards the end of the war, the British started to use tanks to break through trench defenses. The Germans responded with anti-tank guns and mines. Improvised mines gave way to mass-produced mines consisting of wooden boxes filled with guncotton, and minefields were standardized to stop masses of tanks from advancing.
While the Germans were advancing rapidly using blitzkrieg tactics, they did not make much use of mines. After 1942, however, they were on the defensive and became the most inventive and systematic users of mines. Their production shot up and they began inventing new types of mines as the Allies found ways to counter the existing ones. To make it more difficult to remove antitank mines, they surrounded them with S-mines and added anti-handling devices that would explode when soldiers tried to lift them. They also took a formal approach to laying mines and they kept detailed records of the locations of mines.
Mines forced tanks to slow down and wait for soldiers to go ahead and remove the mines. The main method of breaching minefields involved prodding the dirt with a bayonet or stick at an angle of 30 degrees (to avoid putting pressure on the top of the mine and detonating it). Since all mines at the beginning of the war had metal casings, metal detectors could be used to speed up the locating of mines. A Polish officer, Jozef Kosacki, developed a portable mine detector known as the Polish mine detector. To counter the detector, Germans developed mines with wooden casings, the Schu-mine 42 (antipersonnel) and Holzmine 42 (anti-tank). Effective, cheap and easy to make, the schu mine became the most common mine in the war. Mine casings were also made of glass, concrete and clay. The Russians developed a mine with a pressed-cardboard casing, the PMK40, and the Italians made an anti-tank mine out of bakelite. In 1944, the Germans created the Topfmine, an entirely non-metallic mine. They ensured that they could detect their own mines by covering them with radioactive sand, but the Allies did not find this out until after the war.
In the Korean War, land mine use was dictated by the steep terrain, narrow valleys, forest cover and lack of developed roads. This made tanks less effective and more easily stopped by mines. However, mines laid near roads were often easy to spot. In response to this problem, the US developed the M24, a mine that was placed off to the side of the road. When triggered by a tripwire, it fired a rocket. However, the mine was not available until after the war.
In the 1950s, the US Operation Doan Brook studied the feasibility of delivering mines by air. This led to three types of air-delivered mine. Wide Area Anti-Personnel Mines (WAAPMs) were small steel spheres that discharged tripwires when they hit the ground; each dispenser held 540 mines. The BLU-43 Dragontooth was small and had a flattened W shape to slow its descent, while the Gravel mine was larger. Both were packed by the thousand into bombs. All three were designed to inactivate after a period of time, but any that failed to activate presented a safety challenge. Over 37 million Gravel mines were produced between 1967 and 1968, and when they were dropped in places like Vietnam their locations were unmarked and unrecorded. A similar problem was presented by unexploded cluster munitions.
A conventional land mine consists of a casing that is mostly filled with the main charge. It has a firing mechanism such as a pressure plate; this triggers a detonator or igniter, which in turn sets off a booster charge. There may be additional firing mechanisms in anti-handling devices.
Many mines combine the main trigger with a touch or tilt trigger to prevent enemy engineers from defusing it. Land mine designs tend to use as little metal as possible to make searching with a metal detector more difficult; land mines made mostly of plastic have the added advantage of being very inexpensive.