Operation Chenla II or Chenla Two was a major military operation conducted by the Khmer National Armed Forces (FANK) during the Cambodian Civil War. It began on August 20 and lasted until December 3, 1971.
During the days of Prince Norodom Sihanouk's rule in Cambodia in the 1960s, the North Vietnamese Army (NVA) and their Viet Cong (VC) allies were able to use base areas in Cambodian territory in order to provide logistical support for their combat troops within South Vietnam. Following the March 1970 coup led by the pro-U.S. General Lon Nol, the North Vietnamese aggressively expanded their control over the provinces of northeastern Cambodia, coming dangerously close to the capital Phnom Penh.
Initially, the small, largely untrained and poorly-equipped Cambodian Army (ANK) was not up to the challenge, especially against the larger and more experienced VC and North Vietnamese forces. However, by the summer of 1971, and with massive American and South Vietnamese assistance, the ANK grew into a force of more than one-hundred thousand men.
During the period between September 1970 and June 1971, the ANK won its first victories after they successfully dislodged elements of the NVA's 9th Division along Route 13 and in some parts of the Mekong Delta.
By April 1971, Marshal Lon Nol decided to renew the offensive against the Communist forces, taking advantage of the high morale among the Cambodian Army troops following the partial success of Operation Chenla I. For the Khmer National Armed Forces (FANK) everything was at stake, as many reserves and prestige were invested in the operation. The FANK High Command's main objective was to reopen all of Route 6 and to secure the road between Kampong Cham and the isolated garrison at Kampong Thom. A ANK task-force of ten infantry battalions – again including a large percentage of Khmer Krom troops – gathered into three brigade groups supported by armour and artillery was assembled for the operation, which relied heavily on U.S. air support to soften an estimated two NVA divisions in the region.
Operation 'Chenla II' was launched on 20 August 1971, again catching the enemy by surprise. Initially, the ANK task-force commanded by Brigadier-General Hou Hang Sin achieved their objective, as the Cambodians were able to retake Barai on August 26 and Kompong Thmar on September 1. But as ANK formations were advancing towards enemy-held territory along Route 6, they were heavily exposed to enemy attacks without adequate protection from the flank. There was heavy fighting as the ANK 5th Brigade Group advanced towards Phnom Santuk while Tang Krasang was retaken on September 20. On October 5, three ANK brigades were committed to capture the areas around Phnom Santuk. The fighting there grew in intensity as the Cambodians and the NVA engaged in heavy hand-to-hand combat. Phnom Santuk was eventually retaken, and the first phase of Chenla II was declared officially concluded on October 25, although real military success had not yet been secured.
Victory celebrations had hardly started at Phnom Penh when on the night of October 26, barely hours upon the conclusion of the consolidation efforts of the second phase of the operation, the North Vietnamese 9th Division, reinforced by the 205th and 207th VC Regional Regiments, launched an all-out assault on the Cambodian positions located along Route 6 from the Chamkar Andong rubber plantation. At the same time, the ANK 14th Battalion at Rumlong was encircled and isolated. During the following days, the 118th, 211th and 377th Battalions were forced to retreat to Tang Kauk, while the 61st Infantry Brigade pulled back to Treal, held by the 22nd Battalion.
The Cambodian army launched an unsuccessful counter-attack on October 27, and the Cambodian corridor along Route 6 was crushed by Communist troops after weeks of heavy fighting. The elements of the NVA 9th Division then launched a final attack which ripped apart several ANK and Khmer Krom battalions, causing the disorganized Cambodian troops to abandon several key positions on December 1. The operation was terminated two days later.
For the Communist forces the battle ended with a decisive victory, as North Vietnamese and Vietcong troops were able to secure their strongholds in northeastern Cambodia without having to expand their control inside Cambodian territory. As usual, another battlefield victory for the North Vietnamese meant another propaganda opportunity. On December 8, 1971, North Vietnamese propaganda boasted that "By October, that is, in two months, the operation was stalemated and 4,500 enemy troops were annihilated and hundreds more captured. The 2nd and 43d Brigades were badly battered. Ten battalions and seven companies of infantry and a tank company were mauled, 39 combat vessels were sunk or set afire, nine aircraft were downed and seven 105mm artillery pieces, many vehicles and large quantities of military equipment were destroyed".2
Indeed, the final attack on Cambodian Army positions during the month of December virtually wiped out ten infantry battalions (including the sacrifice of the best Khmer Krom battalions) and resulted in the loss of another ten battalions-worth of equipment, which included two howitzers, four tanks, five armoured personnel carriers, one scout car, ten jeeps, and about two dozen other vehicles. Militarily and psychologically, the damage suffered during Operation Chenla II was a big one from which the Cambodians would never recover. From then on, the Republican government focused on consolidating its hold over the key urban centers, the main garrisons and the lower Mekong-Bassac river corridors, thus leaving most of the countryside virtually open to Khmer Rouge recruiting drives.