 During the Vietnam War and the Laotian Civil War, Phou Pha Thi mountain was an important strategic outpost which had served both sides at various stages of the conflict.In 1966, the United States Ambassador to Laos William H. Sullivan approved a plan by the USAF to construct a TACAN site atop Phou Pha Thi; at the time they lacked a navigation site with sufficient range to guide US bomber aircraft to their targets in North Vietnam.In 1967 the site was upgraded with the air-transportable all-weather AN/TSQ-81 radar bombing control system.