Air operations Campaign 74B (2 February–30 April 1971) was a major combined arms offensive by the People's Army of Vietnam (PAVN) during the Laotian Civil War.

The PAVN 316th Division—reinforced by artillery, tanks, and sappers—attacked during a period of slackened tactical air support for General Vang Pao's guerrilla army; Operation Lam Son 719 was being waged at the same time.

Having captured the highly strategic Plain of Jars during Operation 74B, the Communists attackers managed to penetrate deeply enough to fire upon the main guerrilla base at Long Tieng.

Using aerial mobility to outmaneuver the Communists, the Royalists managed to stave off defeat until the Vietnamese had to withdraw due to lack of supplies.

As the Communist offensive wilted, Vang Pao was pressured by his backers in Washington, D.C. to ramp down operations to encourage peace talks to settle the war.

The Hmong general compromised by staging an "active defense" of limited spoiling counterattacks to regain ground in the aftermath of Campaign 74B.

There Royalist Hmong guerrillas trained by the Central Intelligence Agency (CIA) and backed by air power fought it out with People's Army of Vietnam (PAVN) regulars.

Hmong General Vang Pao directed a series of offensives dependent on air superiority blasting a way for his guerrillas.

[6] The Communists retaliated with the massive combined arms Campaign 139, running from 13 September 1969 to 25 April 1970, which nearly won them the war.

[7] The aptly named monarchist Operation Counterpunch, fought from 26 September 1969 through 7 January 1971, barely kept the Royal Lao Government in the war.

Bataillon Infanterie 17 (BI 17) from the allied Forces Armee Neutralistes (FAN) garrisoned the forward fighter base at Muang Soui.

Groupement Mobile 21 (GM 21) had been stationed at the old Project Momentum base at Ban Padong to recuperate from service in Operation Counterpunch.

To discourage close air support for the Thais, the North Vietnamese moved in heavy machine guns ringing the site for antiaircraft defense.

Beginning at midnight 13 February, Dac Cong commandos took the major guerrilla base at Long Tieng under fire with a DK-82 recoilless rifle.

The chaotic situation was not helped by Vang Pao's overnight absence in Udorn, Thailand; the Hmong partisans of L'Armee Clandestine depended upon his orders.

[9] If the paucity of air support were not problematic enough, on 14 February,[15] an F-4 Phantom II inadvertently dropped cluster munitions on civilian dependents.

Landed on 28 February 1971, Groupement Mobile 31 (GM 31) was tasked with sweeping north from Skyline Ridge overlooking Long Tieng.

The newly arrived battalions were directed against Phou Tham Seh, a high point three kilometers north of Skyline Ridge.

[13] On 1 April, GM 31 was withdrawn from its quiet sector on the bank of the Nam Ngum; its new position was eight kilometers east of Sam Thong, protecting its flank.

As a result of this accident, which aborted the relief expedition, it was decided to attach a forward air guide to each Thai battalion.

However, instead of fleeing to Hill 1663, they moved south toward Bataillon Infanterie 14 (BI 14) atop Phou Long Mat, suffering middling casualties in the process.

His American backers were urging him to go on the defensive as a means of aiding peace negotiations to end the Laotian Civil War.

[18] On 18 April 1971, two battalions from two Hmong Groupement Mobiles (GMs) pushed 15 kilometers southeast from Ban Pa Dong to settle upon Pha Phai.

The two guerrilla regiments were now poised to move on the Lat Sen airstrip and to link up with GM 23 to take the mountaintop positions at Phou Seu, in a repeat of Kou Kiet.

Vang Pao knew that his hodge podge irregular army of tribal guerrillas and Thai mercenaries were the last Royalist fighting forces in the Kingdom.

And with a decade of experience in trying to hold fixed positions with guerrillas, he knew there was little chance L'Armee Clandestine could stand off a combined arms assault by PAVN regulars.

[25] On 24 June, BC 609 was transferred via air from Hill 1663 to Phou Theung, freeing GM 22 to move eastward to interdict Route 4.

The newly formed Groupement Mobile 24 (GM 24), accompanied by CIA adviser George Bacon, was committed and ended its sweep by occupying Phou Seu on 29 June 1971.

[25] Phou Theung had been captured without seeking agreed upon advance approval from Henry Kissinger; he was informed that Vang Pao had only given notice of that offensive move after it was in progress.

Nevertheless, both the State Department and CIA Headquarters were uneasy about King Sisavang Vatthana and Prime Minister Souvanna Phouma pushing Vang Pao into an unacceptably risky offensive.