Being essentially a continuation of the old Royal armed forces under a new name, the FANK played a more partisan role in the Cambodian Civil War that escalated following the deposition as Head of State of Prince Norodom Sihanouk by a coup d’état in March 1970 orchestrated by his own Prime-Minister General Lon Nol and cousin Sirik Matak.

Under the terms of the Geneva Accords signed the following year which ended the Indochina War, French Army and Vietnamese Vietminh guerrilla units still operating in Cambodia were obliged to withdraw from its territory and that a new defense force was to be raised.

Meanwhile, Cambodia was admitted as a protocol state member of the US-sponsored SEATO alliance and under his command the FARK became a bastion of American influence on the Sihanouk regime, particularly because US military aid constituted 30% of the armed forces’ budget until August 1964, when it was renounced by the Cambodian government.

Lon also knew that Sihanouk's balancing appeasement of the US from 1968 onwards by allowing B-52 aerial bombings and ‘hot pursuit’ cross-border raids against NVA/VC base areas within Cambodia would be ineffective in stopping the wider, home-grown communist insurgency.

On March 17, 1970, while Sihanouk was absent from the country on a state visit to China and the USSR, Lon Nol assumed power when the National Assembly in Phnom Penh unanimously voted the Prince out of office.

Lon Nol automatically succeeded the latter as Head of State on August 18, and although he claimed that the move was constitutionally legal, it quickly ran afoul of the conservative mentality of the Cambodians, many of whom believed that the Prince ruled through divine favour.

To further aggrieve matters, Prince Sihanouk, who had sought refuge in China after being deposed, established a political base in Beijing and entered into an alliance with the increasingly Maoist-oriented Khmer Rouge leadership and other leftist opposition groups.

By contrast, new recruits were readily available from the ranks of the far-right Khmer Serei, a US-backed anti-communist guerrilla group led by the hardline Nationalist Son Ngoc Thanh which had fought against Sihanouk's regime during the 1960s and who always viewed him as a communist crony.

In reality, the newly created Khmer Republic and its ill-prepared armed forces were soon caught off-guard in the early 1970s by the aggressive reaction of the NVA, which had previously limited its actions to providing support to Vietcong units operating at South Vietnam even after its devastating defeat in the January 1968 Tet Offensive.

[5][6][7] The creation of the Chinese-sponsored FUNK coalition by Sihanouk and the lending of his popular support to the anti-Republican insurgency gave it greater legitimacy in the eyes of the pro-Sihanoukist Cambodian peasantry, many of whom began to flock into its ranks.

In the wake of the January 1973 Paris Peace Accords, Lon Nol proved unable to halt the illegal build-up of North Vietnamese forces in the lower Mekong-Bassac area in preparation for a renewed offensive in neighbouring South Vietnam.

After mid-1971, the Republican government focused on consolidating its hold over the key urban centers, the main garrisons and the lower Mekong-Bassac corridors, thus leaving most of the countryside virtually open to Khmer Rouge recruiting drives.

While the CPNLAF was far smaller, the FANK High Command was always faced with the problem of how to provide adequate equipment for the swelling number of volunteers who flocked to fight the NVA and the Khmer Rouge from their dwindling stocks.

[10] Even though their government had surrendered, FANK soldiers continued to fiercely hold their ground for nearly a month after the fall of Phnom Penh against several unsuccessful attempts by Khmer Rouge forces to reduce this last holdout.

Their roles were defined as follows: to guarantee the sovereignty of the nation and that of the King; to ensure internal security by maintaining the social order and the rule of law; and to defend the newly independent Kingdom of Cambodia from external threats.

The FANK comprised the following branches: The Air Force Academy was transferred from Pochentong to the provincial capital of Battambang whilst the Officer Candidate School was moved from Phnom Penh to Longvek in Kampong Chhnang Province, just north of Oudong.

[22] Special Forces' (SF) courses were undertaken at the LLDB Training Center at Dong Ba Thin Base Camp near Cam Ranh Bay, South Vietnam,[23] but also in Thailand, at the Royal Thai Army (RTA) Special Warfare Center at Fort Narai, Lopburi province, while Guerrilla and 'Commando' techniques were taught by the Royal Thai Police (RTP) Police Aerial Resupply Unit (PARU) at their Phitsanulok and Hua Hin training camps.