The Trường Sơn Trail (better known as the Hồ Chí Minh Trail) was a logistical system that ran from the Democratic Republic of Vietnam (DRV) of North Vietnam, along the Annamite range mountains, through the kingdoms of Laos and Cambodia, to the Republic of Vietnam (RVN) of South Vietnam. Work on the Trail started in 1959 by Group 559, a logistical and transport unit of the People’s Army of Vietnam (PAVN), followed by Group 759 and Group 959 later that same year. The system provided support in the form of manpower, equipment and supplies to the PAVN, the National Liberation Front (NLF)and its Việt Cộng guerilla components during the Second Indochina War (1955-1975) against RVN and America. The Trail in the Annamite range is the site of the single most intense bombing campaign in history, with bombs dropping on average every seven minutes.