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Last Updated: Thursday, 15 June 2006, 15:49 GMT 16:49 UK
Claymore mines: Ingenious and deadly

Claymore mines - like the one thought to have been used to blow up a bus in Sri Lanka - are deadly explosive devices widely used around the world.

Unlike most mines, claymores are placed on top of the ground rather than underneath, and can be detonated remotely at a moment for maximum impact. They fire steel shrapnel as far as 250 metres in a fan shape in front of where they have been placed.

The claymore technology originates from World War II, when German and Hungarian scientists discovered independently that placing explosives in front of a metal plate meant that the force of the blast could be concentrated in a particular direction.

The technology was not fully developed in time for use in World War II, but in post-war research the US created a device - the M18 - that fired ball-bearings forwards at high speed.

The curved device could be placed above ground and pointed towards enemy positions.

After more refinements, the device was replaced by the M18A1, and was widely used during the Vietnam War, either to ambush enemy troops or to protect dug-in soldiers from enemy attack.

Ambush weapon

The M18A1 consists of a plastic casing 21cm (8in) long, 8cm (3in) high, and 3 cm (1.5in) deep, standing on two adjustable legs.

The plastic casing contains a steel sheet at the back, and at the front 680g of plastic explosives and 700 steel balls. It also has a viewing hole so that troops placing it can get an accurate picture of the area being targeted.

Claymore mine
The mine can send shrapnel 250 metres away
The device fires the balls in a 60-degree horizontal arc, inflicting its most deadly damage within 50 metres but potentially causing injury at 250 metres.

The balls reach a maximum height of two meters from the ground. Troops behind the device are left relatively safe.

The claymores have military advantages over other types of anti-personnel mines, including the key fact that they can be deliberately detonated as troops advance, rather than requiring an accidental triggering by the enemy troops themselves.

The claymores can be set off in a number of ways, including being detonated by a soldier using an electrical wire, or can be set off on a timed delay.

Claymores can also be set off by motion or acoustic sensors. Several can be set off at once.

Though designed for use against troops, the powerful blast can also be dangerous to soft-skinned vehicles such as buses and trucks.

In the Sri Lanka attack, reports suggest the claymore device had been left in a tree for even greater impact, to avoid any force from the blast being absorbed by the ground.

The term claymore has been used as a catch-all term to describe many other devices of a similar design, built in countries such as the Soviet Union, the former Yugoslavia, Israel and South Africa.

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