The Ho Chi Minh trail was a supply route that ran from North Vietnam, through Laos and Cambodia, and into South Vietnam. It provided a means to move men and materiel to the battle fronts in the South. According to the U.S. National Security Agency’s official history of the war, the Trail system was “one of the great achievements of military engineering of the 20th century.” Although the Ho Chi Minh trail was the target of incessant American bombing, it was continuously rebuilt.