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The Claymore Mine

By Kevin Dockery

The lessons of island fighting in the Pacific during World War II were not lost on one of the post-war residents of Los Angeles. Norman A. MacLeod knew of the terrible cost to U.S. Forces when they faced massed Japanese banzai charges in the deep darkness of the jungle nights. Even rapid fire from groups of automatic weapons couldn’t always break the human wave of a massed assault. Only something like a giant shotgun would break up such an attack. MacLeod thought he knew of a way to develop just such a giant shotgun.

Approaching the Marine Corps with his idea in 1949, MacLeod had the good fortune to meet up with a reviewing officer who recognized a good idea when he saw it. Material, assistance, range, and testing facilities were made available and MacLeod’s design was developed.

In 1956, a patent for the new weapon was applied for by MacLeod and was awarded on 28 February, 1961. Being a good Scotsman, MacLeod named his “Anti-Personnel Fragmentation Weapon” the Claymore, after the massive two-handed Scot battle sword. And the new Claymore mine could sweep through massed ranks of men much like those legendary swords that were its namesake.

The original M18 Claymore mine had a slightly curved plastic body holding a 3/4 pound charge of C4 plastic explosive. In front of the C4, along the convex side of the body, were hundreds of steel balls that would act as the fragmentation projectiles of the weapon.

Set up on its three folding metal legs, or tied to a convenient tree or other support by the two cloth flaps on either end of the mine, the Claymore could be aimed like a shotgun. When fired by its battery pack firing device, the M18 Claymore would blast its fragments out in a fan-shaped swarm. The beaten zone of the blast fan of the M18 Claymore was 2 meters high and 30 meters wide at a range of 30 meters. The fragments remained dangerous out to over 200 meters in front of the weapon.

Type classified by the Army in 1959, the M18 Claymore was found to have a number of shortcomings when used by the troops. With a short time a modified weapon, the M18A1 Claymore became standard issue. It has remained standard issue in the US arsenal today.

The M18A1 Claymore’s body is a glass-filled polystyrene plastic molding produced in two parts. The rectangular mine body is curved outwards towards it’s front in order to control the spread of the fragmentation when the mine is fired. Inside the front portion of the mine body is the fragmentation matrix consisting of 700 steel balls held in place with a plastic resin.

The rear of the mine body holds the charge of C-4 explosive. Detonation of the C-4 blasts the fragmentation outwards in an expanding arc with a velocity of about 3,000 feet per second (914 m/s. The design of the Claymore’s body is such that the spread of the fragmentation remains in a 60 degree fan-shaped beaten zone 2 meters high and 50 meters wide at a distance of 50 meters from the point of detonation. This area of maximum effectiveness is called the killing zone of the mine and is one of the significant improvements of the M18A1 over the earlier M18 model.

Within the killing zone of an M18A1 Claymore, the fragmentation has a high enough velocity to penetrate a standard US Army armored vest. And additional area of moderate effectiveness extends outward from the mine to a distance of 250 meters. The area of moderate effectiveness is also wider than the killing area and covers an arc 90 degrees to the right and left of the center of the killing zone.

Because of the blast of explosive when a Claymore is fired, all personnel must be undercover when within 100 meters of the mine and no one should be within 16 meters of the point of detonation. With the 16 meter danger area of a Claymore, the backblast of the explosive can cause concussion injuries of personnel, even when they are under cover.

Even when friendly personnel are undercover and at a proper distance, the power of a Claymore going off can be staggering. In a large ambush, where a number of Claymores are fired at one time, the effect is incredible, even when the operators know what is coming. During one PRU ambush operation in Vietnam, the SEAL advisor had over a dozen M18A1 Claymores laid out, and fired them all in a single shot.

“The mines going off sounded like an ARC LIGHT strike (B-52s w/500 lb bombs). Then my PRUs opened up, covering the entire area with a swath of fire. As the firing stopped, there was only dust and a ringing kind of silence.”

Mike Boynton USN (Ret.) Excerpted from “Hunters and Shooters,” Edited by Bill Fawcett. Avon Books: New York. 1995. Page 122

Just about all of the troops who used the Claymore mine liked it. The sudden blast of firepower coming out from a Claymore, or a line of Claymores, could wipe out an incoming group of enemy forces, or cause them to break up in confusion where they could be picked off one by one.

One of the primary uses of the Claymore was for area defense. Positions such as firebases, hilltops, or even just a few holes in the ground and some cover, could be quickly defended by a ring of Claymores. Another very popular use for the Claymore was as an ambush weapon. When properly laid out and aimed, the Claymore could literally sweep an area clear of vegetation, and any personnel who might be there.

The Claymore comes complete in a bandoleer with everything necessary to employ it. The firing system supplied is electrical and includes an M4 blasting cap, an M6 special electric cap attached to 100 feet of firing wire, and a squeeze-type M57 firing generator intended to fire a single cap.

The Claymore can be set up with the M4 blasting cap inserted into either of the cap wells at the top of the mine’s body and secured in place with the screw plugs provided. The 100 feet 30.48 m) of firing wire attached to the cap is unwound from it’s spool out to the firing position. At the position, the shorting plug is removed from the firing wire and the wire’s end plugged into the M57 firing device, also called the “clacker”.

The M57 clacker has a safety bale that prevents the operating handle from being depressed unintentionally. Moving the safety bale on the firing device allows the handle to be squeezed, firing the mine. To test the firing circuit of the Claymore without firing it, an M40 test set is supplied, one per case of mines. The bandoleer of the mine kit containing the M40 test set is marked by a green tag on the shoulder strap of the bag.

The M40 test set itself is a simple green box that has a socket to accept the M57 firing device at one end and a plug intended for the M4 blasting cap assembly at the other end. By placing the M40 test set into the circuit, the firing system can be tested by squeezing the firing device. If the circuit is sound, a visible light will flash in the test set without setting off the cap. Simply removing the test set and plugging the M4’s wire into the M57 firing device readies the Claymore for firing.

In the humid and corrosive environment of Vietnam, even testing a setup M18A1 Claymore didn’t guarantee the mine would go off. Even mines that tested positive seemed to have a mind of their own on occasion. During one operation in the T-10 area of the Rung Sat Special Zone, a squad of SEALs had laid out an ambush for a number of VC thought to be operating in the area. As a group of 10 to 15 armed VC walked into the kill zone of the ambush, the SEAL officer in charge prepared to trigger the ambush.

“Whispering, I said, “Claymore!” The VC were right there, 30 feet away. We would have had them cold. We wouldn’t have had to fire a shot. Only the damned Claymores didn’t go off. We cranked them two or three more times and they still didn’t go off. I couldn’t believe it. Still on all fours, I said, “Open up,” to the Stoner man and the whole squad started shooting...

... we called in slicks and left in style, guns blazing and the Seawolves hosing the place down. We tried the Claymores one last time before the helos came in. The damned things went off. Lesson: explosives can be unreliable so you’d better have a backup plan.”

Captain Rick Woolard USN (Ret.) Excerpted from “Hunters and Shooters,” Edited by Bill Fawcett. Avon Books: New York. 1995. Page 238

Even with the occasional disappointment, the M18A1 Claymore mine earned itself a solid place in the US arsenal. Use of the mine was only limited by the operator’s imagination. Claymore’s were used as boobytraps, base defense, and as a counter-ambush device when a group of US forces were trying to break contact with an pursuing enemy force. For this kind of use, a prepared Claymore would be carried by the squad, outfitted with a non-electric firing system and a 30-second time delay.

The chased squad could quickly emplace the Claymore to cover the path behind them. Pulling the fuse igniter on the Claymore would start the delay and the squad would pull out. As the pursuing VC would come after the squad, they would often run right into the killing area of the mine as the Claymore detonated. The simple act of setting up the Claymore and pulling the fuse actually takes longer to describe than to do.

Some applications of the Claymore worked better than others, Some just never worked at all. One young officer had the idea of lining the sides of a truck with Claymore mines, just the thing to break up a VC ambush. But even with a heavy lining of sandbags, and an armored cab, the truck would only stand up to one such firing before being turned into a twisted pile of junk. And it was very hard to find a soldier who was willing to sit, even in an armored cab, and allow a bunch of Claymore mines to go off all around him.

Probably the biggest compliment to the efficiency of the Claymore mine is the fact that it is the most copied directional mine in the world. Even the Viet Cong worked hard in their jungle workshops to turn out their versions of the Claymore. The VC DH-10 directional fragmentation mine was around a foot in diameter and weighed over 30 pounds. But it could blast its cut-up steel rod fragmentation out to over 200 meters and take out personnel. Closer in, the DH-10 could destroy vehicles and even bring down helicopters.

M18A1 Claymore mine

TYPE: Directional antipersonnel fragmentation mine


CONTAINER MATERIAL: Fiberglass filled polystyrene plastic


METHOD OF ACTUATION: Military blasting cap or primacord; Command detonated with the M57 firing device and M4 electric blasting cap; Remote detonated with a military blasting cap or primacord and a suitable firing device

EFFECTS: Blast drives 700 10.5 grain (0.68 g) steel spheres out in a 60 degree fan-shaped sheaf (arc) from the point of detonation

AREA OF EFFECT: (16 m) Blast radius from C4 explosion; Highly effective fragmentation in an area 55 yds (50 m) wide by 2.7 yds (2.5 m) high, 55 yds (50 m) in front of the point of detonation

LENGTH: 8.5 (21.6 cm) M18A1 Mine; 4 in (10.2 cm) M57 Firing device; 100 feet (30.48 m) firing wire M4 blasting cap

WIDTH (DIAMETER): 1.38 in (3.5 cm) M18A1 Mine; 1.35 in (3.4 cm) M57 Firing device

HEIGHT: 3.25 in (8.3 cm) M18A1 Mine w/legs folded; 3.25 in (8.3 cm) M57 Firing device

EFFECTIVE RANGE: 109 yds (100 m)

MAXIMUM RANGE: 273 yds (250 m) Forward danger radius; USE Local defense of fixed installations and forward areas. Antipersonnel/antivehicular ambushes and directional minefields


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