one of many programs under Trail Dust. The aircrews charged with spraying the defoliant used a sardonic motto-"Only you can prevent forests"-a shortening of the U.S. Forest Services famous warning to the general public "Only you can prevent forest fires". The United States and its allies officially claims that herbicidal and incendiary agents like napalm fall outside the definition of "chemical weapons" and that Britain set the precedent by using them during the Malayan Emergency. Ranch Hand started as a limited program of defoliation of border areas, security perimeters, and crop destruction. As the conflict continued, the anti-crop mission took on more prominence, and (along with other agents) defoliants became used to compel civilians to leave Viet Cong-controlled territories for government-controlled areas. It was also used experimentally for large area forest burning operations that failed to produce the desired results. Defoliation was judged in 1963 as improving visibility in jungles by 30–75% horizontally, and 40–80% vertically. Improvements in delivery systems by 1968 increased this to 50–70% horizontally, and 60–90% vertically. Ranch Hand pilots were the first to make an accurate 1:125,000 scale map of the Ho Chi Minh trail south of Tchepone, Laos by defoliating swaths perpendicular to the trail every half mile or so. Use of herbicides in Vietnam caused a shortage of commercial pesticides in mid-1966 when the Defense Department had to use powers under the Defense Production Act of 1950 to secure supplies. The concentration of herbicides sprayed in Operation Ranch Hand was more than an order of magnitude greater than that in domestic use. Approximately 10% of the land surface of South Vietnam was sprayed—about 17,000 square kilometers. About 85% of the spraying was for defoliation and about 15% was for crop destruction. War on drugs in South America and Afghanistan Types of herbicides The United States had technical military symbols for herbicides that have since been replaced by the more common color code names derived from the banding on shipping drums. The US further distinguished between tactical herbicides, which were to be used in combat operations and commercial herbicides, which used in and around military bases, etc. In 1966 the United States Defense Department claimed that herbicides used in Vietnam were not harmful to people or the environment. In 1972 it was advised that a known impurity precluded the use of these herbicides in Vietnam and all remaining stocks should be returned home. In 1977