The M18A1 antipersonnel mine was standardized in 1960, and replaced the M18 antipersonnel mine. Both mines are similar in appearance and functioning. The M18A1 claymore mine is a fragmentation munition that contains 700 steel balls and 682 grams of composition C4 explosive. It weighs 1.6 kilograms and can be detonated by command It is activated by electric or nonelectric blasting caps that are inserted into the detonator well. When employed in the controlled role, it is treated as a one-shot weapon. It is primarily designed for use against massed infantry attacks; however, its fragments are also effective against light vehicles. The M18A1 mine is equipped with a fixer plastic slit-type sight (knife-edge sight on later model), adjustable legs, and two detonator wells. The number of ways in which the Claymore may be employed is limited only by the imagination of the user. The Claymore is used primarily as a defensive weapon, but has its application in the offensive role. It must be emphasized that when the Claymore is referred to as a weapon, this implies that it is employed in the controlled role. In the uncontrolled role, the Claymore is considered a mine or boobytrap. When detonated, the M18A1 mine will deliver its spherical steel fragments over a 60? fan-shaped pattern that is 2 meters high and 50 meters wide at a range of 50 meters. These fragments are moderately effective up to a range of 100 meters and can travel up to 250 meters forward of the mine. The optimum effective range (the range at which the most desirable balance is achieved between lethality and area coverage) is 50 meters.