Air operations Campaign 139 (14 September 1969–25 April 1970) was a major military offensive of the People's Army of Vietnam, launched against its Royalist enemies during the Laotian Civil War.

They overran the nearby refugee center at Sam Thong on 18 March 1970, and temporarily occupied the high ground overlooking the Lima Site 20A airstrip at Long Tieng used for resupplying the guerrillas.

[2] As the Laotian Civil War flared, it became apparent that the People's Army of Vietnam would be opposed by Lao guerrilla forces backed by air power.

Manning newly supplied 155 mm howitzers, and reinforced by PT-76 amphibious tanks captured from the communists, BV 26 retook Xieng Khouangville on 27 November 1969.

On 2 December, Dac Cong sappers bombarded the position with about 300 rounds of mortar fire, followed by a night assault using improvised Bangalore torpedoes.

He did pull in the ADC militia and their dependents from the last advanced guerrilla outpost at Houei Tong Ko near the Pathet Lao headquarters at Xam Neua.

On 9 January, sappers of the 27th Dac Cong Battalion thrust at Phou Nok Kok from two directions while foul weather precluded tactical air strike support of the Royalists.

Special Guerrilla Unit 1, (SGU 1), a battalion newly arrived from Military Region 4, initially held their ground despite their unfamiliarity with the position and its surrounding terrain.

On 15 January, 183 Royalist soldiers from BV 26 were landed on a ridge directly across Route 7 from Phou Nok Kok in an abortive effort to retake it.

The Royalist irregulars retreated and exfiltrated, opening the way for two PAVN combat engineer regiments to move in and begin improving Route 72 for an advance on Xieng Khouangville.

On the 23rd, American ambassador G. McMurtrie Godley requested supporting Arc Light strikes by B-52 Stratofortresses to bomb an opposing enemy concentration along Route 7.

[25] Meanwhile, Vang Pao decided to use his guerrilla army's air superiority to hopscotch over the opposing communist forces and occupy a mountain top behind them.

By 7 February, a 155 mm howitzer and Royalists from BV 26 occupied a 1,394 meter peak in the rear of the communists, overlooking the 7/71 junction and capable of interdicting PAVN lines of communication by fire.

The following day, the 148th and 174th PAVN Regiments infiltrated under cover of a fog bank to overrun the 7/71 road fork and captured the 155 mm howitzer abandoned there.

Approved personally by President Richard M. Nixon, the three plane strike was aimed at a suspected North Vietnamese headquarters at the eastern limits of the Plain of Jars.

Air strikes were called in to destroy abandoned Royalist equipment, including five captured communist tanks, 12 recoilless rifles, two 105 mm howitzers, and seven trucks.

The Royalist Special Guerrilla Unit 2 moved 18 kilometers southwest under air cover and set up a defensive position blocking a southern exit from the Plain.

On one axis, both the 866th Independent and 165th Regiments bypassed Xieng Khouangville to attack the Royalist Special Guerrilla Unit 4 stronghold at Khang Kho.

The PAVN regiments then penetrated further into Royalist territory, fetching up one ridgeline short of the main guerrilla base at Lima Site 20 Alternate.

Prime Minister Souvanna Phouma, who was a Neutralist, used private channels to let it be known the RLG would halt their military operations against the Ho Chi Minh Trail if the communists agreed to a ceasefire in northern Laos.

[18] On 13 March 1970, contingency planning began for evacuation of noncombat personnel from Long Tieng and Sam Thong, as Vang Pao again mulled moving his Hmong community toward the Thai border.

On 17 March, emergency evacuation of Royalist wounded, Laotian civilians, and Americans from Sam Thong began despite continuing wretched flying weather.

As the weather broke, a Royal Thai Artillery battalion of 300 trained regulars, Special Requirement 9 (SR 9), flew in to set up their guns on high ground southwest of the strip, near Sisavang Vatthana's villa.

RLAF Thai mercenary pilots also attacked, using the Lima strip at Moung Kassy as an improvised forward base as it was nearest to the Plain except Muang Soui.

[36] On 22 March, stragglers from the Ban Na outpost began to regroup on Skyline Ridge as 122 mm rockets continued to bombard Long Tieng.

By 26 March, having advanced with steadily increasing tactical air support as weather cleared, they were perched on hilltops south of Sam Thong.

The two battalions imported from MR 3 had completed their ranks; they now moved north from Long Tieng and swept the communists from the top of Phou Phasai.

On 3 April, CIA case agent Will Greene promised his 3 Special Guerrilla Battalion $3 per day combat pay for moving into the attack.

[37] Although PAVN had failed in its effort to eliminate the Royalist guerrilla army from Military Region 2, it had left the RLG irregulars in sad shape.

Worse yet, some of the ad hoc units hastily formed for defending MR 2 consisted of mixed ethnicities, with inevitable inter-group tensions.