Operation Momentum was a guerrilla training program during the Laotian Civil War. This Central Intelligence Agency operation raising a guerrilla force of Hmong hill-tribesmen in northeastern Laos was planned by James William Lair and carried out by the Thai Police Aerial Reinforcement Unit. Begun on 17 January 1961, the three-day Auto Defense Choc (Self Defense Shock) course graduated a clandestine guerrilla army of 5,000 warriors by 1 May, and of 9,000 by August. It scored its first success the day after the first ADC company graduated, on 21 January 1961, when 20 ADC troopers ambushed and killed 15 Pathet Lao.

The Momentum technique of parachuting in equipment to train guerrillas was so successful it would be copied widely by the Americans during the Vietnam War. The United States Special Forces used the Momentum pre-palleted equipment and their own cadre of instructors for such copycat programs as Operation Pincushion, and for organizing the Degars of South Vietnam.

The success of Operation Momentum brought about more extensive training for the Hmong and other hill tribes recruits such as the Lao Theung. Further training of Special Operating Teams of ADC graduates was begun in August 1961, with the aim of gradually replacing foreign trainers with Lao instructors. In July 1962, the International Agreement on the Neutrality of Laos put a damper on Momentum operations until the following April. During this lull, Colonel (later Major General) Vang Pao gathered five ADC companies into a battalion-sized Special Guerrilla Unit. In later years, he would take the next step of organizing makeshift regiments of SGUs.

Even as Operation Momentum expanded and spread throughout Laos, the burgeoning war in Vietnam became the focus of the American effort; the Laotian Civil War was subordinated to it. The change in emphasis can be judged by the fact that in 1967, the U.S. sank 431,000 troops into the Vietnam theater, at a fiscal cost about 700 times as great as the budget for the Lao war. As the Hmong irregulars joined the Royal Lao Army regulars in joint operations, the role of the hill tribes guerrillas began to mutate into that of light infantry defending fixed positions. The Momentum Hmong guerrillas suffered irreplaceable casualties as a result. By 1973, the Hmong had suffered 18,000 to 20,000 soldiers killed in action, with an additional civilian Hmong death toll nearing 50,000. On 14 and 15 May 1975, a belated U. S. aerial evacuation removed 2,500 Hmong to Thailand; however, the majority of the surviving pro-American Hmong were abandoned by the Americans.