Known to the Vietnamese as the Truong Son Strategic Supply Route – after the Truong Son mountain range that forms the border between Vietnam and Laos – the Ho Chi Minh Trail was a network of paths, roads, rivers and oil pipelines that the North Vietnamese used to carry troops and supplies to battlefields in South Vietnam. Initially a series of walking tracks on the Vietnamese side of the border, US air power forced much of the trail network to cross into the jungles of Laos. US forces began an air campaign to reduce the flow of men and materiel along the trail in Laos, dropping bombs, listening devices and even chemicals designed to make the mud stickier. By 1973, the US scaled back its involvement in the war and the trail became a two-lane paved road on the Vietnamese side of the border that was instrumental in the fall of Saigon in 1975. In the 2000s, the Vietnamese began work on the Ho Chi Minh Highway, a major new road following sections of the former HCM Trail. The highway sticks close to the mountains along the Lao border and offers some of the best motorcycling routes in Vietnam.