In addition to rifles and machine guns, U.S. infantry troops were armed with hand grenades (such as the Mark-2), which could be thrown or propelled using rifle-mounted launchers. Mines were used to guard the perimeter around campsites; they could be triggered by trip wires or exploded manually. In terms of chemical weapons, U.S. Air Force planes sprayed more than 19 million gallons of herbicides over 4.5 million acres of land in Vietnam from 1961 to 1972 as part of Operation Ranch Hand, a large-scale defoliation program aimed at eliminating forest cover for North Vietnamese and Viet Cong troops, as well as crops that might be used to feed them. The most commonly used defoliant, a mixture of herbicides containing the toxic dioxin and known as Agent Orange, was later revealed to cause serious health issues–including tumors, birth defects, rashes, psychological symptoms and cancer–among returning U.S. servicemen and their families as well as among large sections of the Vietnamese population.