[3] Late that same year, the 200-strong CFM was amalgamated with 1,014 ex-Royal Khmer Army troops recently transferred to the MRK to form the nucleus of two new marine rifle battalions (French: Bataillons de Fusiliers-Marins – BFM).

With the outbreak of the Civil War in April 1970, plans were drawn by the rechristened Khmer National Navy (MNK) Fleet Command to rapidly expand the CFMK to ten battalions in October, but only four BFMs totalling 3,000 men were fully operational by the end of the year.

This situation lasted until early 1973, when the MNK was once again authorized to double the strength of its Marine Corps, including an ambitious expansion to thirty battalions though the actual number of BFMs never came close.

Due to budgetary restraints, the Marines received insufficient rice rations and were denied hazardous duty pay (French: Prime d'intervention) comparable to that paid by the ANK.

[12] It was to be the final amphibious operation of the Cambodian Marine Corps – despite their best efforts, the weakened BFMs posted in the Mekong Special Zone bore the brunt of the Khmer Rouge offensive and resistance crumbled, with desertions reportedly becoming rampant.

By February 17, the MNK Fleet Command abandoned any attempts to re-open the lower Mekong and Bassac corridors,[13] and with the loss of Neak Leung on April 1, the strangulation of the Cambodian Capital was completed.

Only a few Marines and their civilian dependents managed to escape on April 17 from Ream with the vessels of the MNK Sea Patrol Force that reached Subic Bay in the Philippines on May 9;[14][15] their comrades at the Chrui Chhangwar riverine base who surrendered to the Khmer Rouge were not so fortunate.

Instead, it answered directly to the MNK Chief of Naval Operations, Commodore (later, Rear Admiral) Vong Sarendy, who acted as the de facto Marine Corps' Commander throughout the War.