Claymore Mine

Lore & Background

The M18A1 Claymore mine fires steel balls out to about 300 ft (100 m) within a 60° arc in front of the device. It is used primarily in ambushes and as an anti-infiltration device against enemy infantry. It is also used against unarmored vehicles. Internally the mine contains a layer of C-4 explosive behind a matrix of about seven hundred 1⁄8-inch-diameter (3 mm) steel balls set into an epoxy resin. When the M18A1 is detonated, the explosion drives the matrix forward, out of the mine at a velocity of 3,900 ft/s (1,200 m/s), at the same time breaking it into individual fragments. The steel balls are projected in a 60° fan-shaped pattern 7 feet (2 m) high and 160 ft (50 m) wide at a range of 160 ft (50 m). The force of the explosion deforms the relatively soft steel balls into a shape similar to a .22 rimfire projectile. These fragments are moderately effective up to a range of 330 ft (100 m), with a hit probability of around 10% on a prone man-sized 1.3-square-foot (0.12 m2) target. The fragments can travel up to 800 ft (250 m). The optimum effective range is 160 ft (50 m), at which the optimal balance is achieved between lethality and area coverage, with a hit probability of 30% on a man-sized target.

In Their Own Story

The mine was apparently named by its inventor, Norman MacLeod, after the claymore, a two-handed Scottish sword associated with his Scottish ancestry. The word "claymore" derives from the Scottish Gaelic claidheamh mòr, meaning "great sword." MacLeod applied for a patent for the mine on 18 January 1956, and was granted it in February 1961. The patent was later the subject of a civil court case between MacLeod, the Army, and Aerojet, which further developed the Claymore design. MacLeod's case collapsed when photographs of the German Trenchmine prototype were produced as evidence of prior art. The original M18 was 9.25 inches (235 mm) long and 3.27 inches (83 mm) high, held in a plastic case with three folding spike legs on the bottom. An electrical blasting cap for triggering the mine was inserted through a small hole in the side. Internally the mine consisted of a layer of 12 ounces (340 g) of C-3 explosive (the forerunner of C-4 explosive) in front of which was laid an array of 0.25-inch (6.4 mm) steel cubes. In total the mine weighed about 2.43 pounds (1.10 kg), and could be fitted with an optional peep sight for aiming. It lacked the later version's iconic "FRONT TOWARD ENEMY" marking.

Reader's Guide

The weapon and all its accessories are carried in an M7 bandolier ("Claymore bag"). The mine is detonated as enemy personnel enter the killing zone. Controlled detonation may be accomplished by use of either an electrical or non-electrical firing system. When mines are employed in the controlled role, they are treated as individual weapons and are reported in the unit fire plan. They are not reported as mines; however, the emplacing unit must ensure that the mines are removed, detonated, or turned over to a relieving unit. The 100-foot (30 m) M4 electric firing wire on a green plastic spool is provided in each bandolier. The M57 firing device (colloquially referred to as the "clacker") is included with each mine. An M40 circuit test set is packed in each case of six mines. When the mines are daisy-chained together, one firing device can detonate several mines. The mine can be detonated by any mechanism that activates the blasting cap. There are field-expedient methods of detonating the mine by tripwire, or by a timer, but these are rarely used.

Did You Know?

• The M18A1 Claymore fires steel balls at a velocity of 3,900 ft/s (1,200 m/s).
• The optimum effective range of the M18A1 is 160 ft (50 m), with a 30% hit probability on a man-sized target.
• The mine's inventor, Norman MacLeod, named it after the claymore, a two-handed Scottish sword.
• The M18A1 contains about seven hundred 1⁄8-inch-diameter (3 mm) steel balls set into an epoxy resin.
• The M57 firing device is colloquially referred to as the "clacker."