In late 1971, the People's Army of Vietnam launched Campaign 'Z' into northern Laos, escalating the war in Laos with the aim of defeating the last Royal Lao Army troops. The NVA troops numbered 27,000 and brought with them 130mm field guns and T-34 tanks, while the North Vietnamese air force launched MiG-21s into Lao air space. General Giap's specific orders to this task force were to kill the CIA army under command of the Hmong war lord Vang Pao and occupy its field headquarters in the Long Tieng valley of northeast Laos. They faced the rag-tag army of Vang Pao, fewer than 6,000 strong and mostly Thai irregulars, recruited by the Thai army to fight for the CIA in Laos. By the time the NVA launched their first attack, 4,000 Tahan Sua Pran had been recruited, armed, trained and rushed in position in Laos to defend against the impending NVA invasion. They reinforced Vang Pao's indigenous army of 1,800 Lao hillstribe guerrillas. Despite the odds being overwhelmingly in the NVA's favour, the battle did not go to plan. It raged for more than 100 days, the longest in the Vietnam War, and it all came down to Skyline Ridge. As at Dien Bien Phu, whoever won Skyline, won Laos. Against all odds, against all WDC expectations, the NVA lost, their 27,000-man invasion force decimated. James Parker served in Laos. Over many years he pieced together his own knowledge with CIA files and North Vietnamese after-action reports in order to tell the full story of the battle of Skyline Ridge.