During the Korean War (1950-53), United Nations (UN) forces came under constant infantry attacks from the Chinese and North Korean armies that were reminiscent of the mass charges that the Japanese military had conducted during the Second World War. One counter measure considered was how anti-personnel mines could direct its explosion to address these threats.
The Canadian military first developed a weapon dubbed the “Phoenix,” which contained five pounds of Composition B explosives and quarter-inch steel cubes that could be launched towards an enemy. With a range of just twenty to thirty yards it was considered ineffective given its weight.
Meanwhile Norman A. MacLeod of the Explosive Research Corporation working for the United States military conceived a smaller system that had a longer range and weighed a bit less. Named for a large medieval Scottish sword, the M18 Claymore proved to be the first directional fragmentation mine.
The fan-shaped M18 measured eight and a half inches long by just an inch and three-eighths thick and three and a quarter inches high, weighing only three and a half pounds. The system was compact and could be carried in a bandoleer.
Yet, it packed a serious punch—as it contained 700 steel spheres and a pound and a half of composition C-4 explosive. It was initiated by a number two electric blasting cap, and while originally electrically-actuated, the system was refined so that it could be detonated either in an electrical or non-electrical fashion.
The fragments were moderately effective up to a range of 110 yards/100 meters when employed with obstacles and on approaches against a dismounted infantry attack. The optimal effective range was about half that distance, while wounding has been reported from as far away as 270 yards.
The platform was designed to be somewhat “idiot proof” in that the “active” side was embossed with the words “Front Toward Enemy,” whereas the rear was embossed with “Back” to help keep the M18 Claymore’s operator from making a lethal mistake during setup! However, as MilitaryFactory.com noted even when properly employed the Claymore could be dangerous to anyone in extreme close proximity as up to 20 percent of the internal steel ball projectiles could still blow back toward a friendly line when detonated. The backblast area of around sixteen meters to the rear and sides of the munition was generally considered unsafe.
As such, in the field it was common for the Claymore to be set up with the back facing mounds or other obstacles to help eliminate or at reduce the risk of friendly-fire. Additionally, friendly personnel within 100 meters to the rear and sides were required to note that they should be in a covered position to be safe from secondary missiles.
The improved M18A1, which also featured a peek sight to help the operator determine the “field of vision” when setting up the device, was widely used in the Vietnam War. It proved adaptable for covering the ranges between maximum hand grenade throwing distance the minimum safe distance of a mortar and artillery fire.
Peter Suciu is a Michigan-based writer who has contributed to more than four dozen magazines, newspapers and websites. He regularly writes about military small arms, and is the author of several books on military headgear including A Gallery of Military Headdress, which is available on Amazon.com.