From 4 July 1964 until March 1973, battalions of Thai volunteers fought Communist Pathet Lao insurgents on the Plain of Jars in Military Region 2.
By December 1970, Unity battalions also began defensive operations against People's Army of Vietnam (PAVN) units pushing westward from the Ho Chi Minh trail in the southern Lao panhandle.
As an open effort would attract Chinese attention, the Thai government elected covert participation in the ongoing Laotian Civil War.
[1] As early as September 1958, the Royal Thai Army (RTA) began training Lao troops at Camp Erawan, Thailand.
[3] On 4 July 1964, to prepare for the Laotian offensive Operation Triangle, a Royal Thai artillery battalion of 279 men was flown from Korat, Thailand to the Plain of Jars, Laos.
[5] Succeeding Special Requirement units served as reinforcement of FAN forces stationed at the forward all-weather air strip at Muang Soui.
During Campaign Toan Thang, on 24 June 1969, when People's Army of Vietnam (PAVN) troops had scattered FAN, Special Requirement 8's 317 men manned its guns and held its ground.
[10] During the Vietnamese Campaign 139, which threatened the existence of Vang Pao's L'Armee Clandestine, 300 Thai artillerymen of Special Requirement 9 arrived at Long Tieng.
As the summer progressed, units that had been transferred in from other Military Regions rotated to their home bases, and the Thai infantry replaced them in their strongholds.
[11] In the wake of Lon Nol's ascension to the leadership of the Khmer Republic, in early June 1970 the Royal Thai Government (RTG) raised 5,000 volunteer recruits to serve there, and began training them.
When Lieutenant General Richard G. Stilwell claimed the U.S. budget for training and equipping those troops could pay for retraining the entire RTA instead, he was overridden.
[14] In June 1972, in an effort to boost recruitment for the Unity program, Thai volunteers without prior military training were accepted for service in Laos.
Operating under the code name Virakom, they were so successful that CIA case officers, noting the contrast with the Khmer troops of Project Copper, thought the Thais might recapture the Boloven Plateau for them.
[14] On 27 July 1971, Unity troops were committed to Operation Sayasila in a drive to recapture the vital air strip at Salavan.
[16] By December, the PAVN was pressuring the Royalists in operations designed to push them away from the Ho Chi Minh trail and backwards toward Thailand.
Fire Support Base Puncher, the Ban Na outpost of Long Tieng, was surrounded by PAVN infantry and sappers.
[13] Unity troops held the line through March; PAVN could not overrun Long Tieng and win the war before the rainy season quashed operations.
[22] By the end of 1971, when the North Vietnamese launched Campaign Z, the Thai troops in L'Armee Clandestine had largely replaced the original Hmong militia.
[24] By May 1972, the Hmong manpower pool was so diminished that a CIA paramilitary adviser noted that his newly recruited battalion of guerrillas contained over 100 youths under 17 years of age, with about a dozen being 12 or younger.
[27] When the ceasefire ended the war on 22 February 1973, Unity consisted of 27 infantry and three artillery battalions, along with six heavy weapon companies.