Operation Chenla I

Background

Following the overthrow of the Cambodian head of state, Prince Norodom Sihanouk, in a coup d'état in March 1970 and its replacement by a pro-US Republican government, the re-christened Khmer National Armed Forces (FANK) focused on expelling all North Vietnamese Army (NVA) and Viet Cong (VC) forces from their border sanctuaries in eastern Cambodia after the new President of the Khmer Republic, Marshal Lon Nol, issued an ultimatum. However, from May 1970, the ill-prepared FANK was quickly placed at a strategic disadvantage following the seizure of the northeastern areas of the country (the provinces of Stung Treng, Ratanakiri, Kratie, and Mondulkiri) by the NVA in response to the ultimatum and the loss to the Khmer Rouge insurgents of several peripheral eastern and southwestern Cambodian provinces (Kampot, Koh Kong, Kampong Cham, Preah Vihear, plus portions of Siem Reap, Oddar Meanchey, Kampong Thom, Prey Veng, and Svay Rieng Provinces) during that same year.

In July 1970, the FANK High Command decided to take advantage of a lull in NVA/VC activity as an opportunity to regain the strategic initiave and raise the morale of the Cambodian Army (ANK) troops by retaking large expanses of rich rice-growing areas in northeastern Cambodia not under the Khmer Republic government control. President Lon Nol made preparations for an offensive plan codenamed 'Chenla' to be launched in late August of that same year. An ANK task-force consisting of a dozen infantry battalions – which included several 'repatriated' Khmer Krom volunteer battalions recruited in South Vietnam – supported by armour and artillery was assembled for the operation, which relied on limited ground and air support from the Army of the Republic of Vietnam (ARVN) and the South Vietnam Air Force (VNAF).

The operation

Initially, Operation Chenla I went on as planned. The offensive began in late August, when the ANK task-force under the command of Brigadier-General Um Savuth converged on Route 6 and its objectives were two-fold: firstly, sweep away NVA and VC forces along the road and recapture the rice paddies around Kampong Cham. Secondly, clear Route 7, which was repeatedly attacked by Communist forces, in order to reconnect Skoun and Kampong Thom. The ANK task-force succeeded in catching the enemy by surprise, retaking Tang Kauk during early September with ease and opened 15 miles of Route 6 for a short time; the Cambodian troops then helped resettle refugees and raised local self-defense forces.

In response to this offensive, the NVA/VC forces mounted a series of counter-attacks along Route 7, intended to block the advance of the Cambodian Army units; the areas around Kompong Cham and Prey Totung saw significant fighting during the closing months of 1970. As a result of the pressure exerted by the NVA's 9th Division, the Cambodian army couldn't advance further beyond Tang Kauk. South Vietnamese ARVN units then linked with the Cambodian task-force east of the Mekong River in December, allowing the Cambodian army to reopen Route 7 without making contact with enemy troops.

However, on the night of 21–22 January 1971, a hundred or so-strong NVA (Vietnamese: Dac Cong or 'Sappers') 'Commando' force managed to pass undetected through the defensive perimeter of the Special Military Region (RMS) set by the ANK around Phnom Penh and carried out a spectacular raid on Pochentong airbase, virtually annihilating the then Khmer National Aviation (AVNK) on the ground. The surrounding areas around the airbase were also targeted. President Lon Nol extended the 'State of Emergency' for another six months as some Cambodian Army units fighting at Tang Kauk were recalled and redeployed to protect Phnom Penh, effectively bringing Chenla I to an end.

Consequences

Despite early gains, the Cambodian military only achieved a limited strategic success, with the cost of sacrificing some of the more experienced Khmer Krom battalions; the North Vietnamese and Viet Cong still controlled a large portion of territory east of Phnom Penh. Lon Nol was evacuated by U.S. aircraft for treatment at the Tripler General Hospital in Hawaii after suffering a severe stroke.