When the United States replaced the French in Vietnam, it supplemented the Vietnamese forces with American armed forces and equipment. The most influential area of ​​the military armed forces was the Air Force, as it had the greatest impact on the war effort. Due to the condition of the Vietnamese Air Force, the U.S. Army provided the South Vietnamese Army with the equipment they needed. Between the years 1961 and 1965, the Vietnamese Air Force contingent grew from 68 to 6,600 men and from a few liaison aircraft to 84 different types of aircraft. In Vietnam, the Air Force played an important role in the war effort, as it was able to provide significant assistance to deployed ground troops. At the start of the war effort, the Air Force was not a large enough force to be effective. In 1964, the reconnaissance squadrons used in Laos were disbanded, due to a shortage. During the conflict, the region's tropical climate provided cover for North Vietnamese forces that would make it difficult to locate and engage in combat. As a result, the military had to develop a method to destroy dense vegetation located in combat zones. Another obstacle that American forces in Vietnam faced during the conflict was the inability to identify enemy forces since there were North Vietnamese forces in both North and South Vietnam. As it was common for men in Vietnam to survive by gathering food from the land, the military also had to develop a method that could be used to destroy crops and food sources accessible to enemy forces. Because of these many requirements and obstacles, the military developed the herbicide Agent Orange to target both heavy foliage and present enemy food sources, such as rice.