The Cambodian Campaign (also known as the Cambodian Incursion and the Cambodian Invasion) was a series of military operations conducted in eastern Cambodia during mid-1970 by the United States and the Republic of Vietnam (South Vietnam) during the Vietnam War. These invasions were a result of the policy of President Richard Nixon. A total of 13 major operations were conducted by the Army of the Republic of Vietnam (ARVN) between 29 April and 22 July and by US forces between 1 May and 30 June.
The objective of the campaign was the defeat of the approximately 40,000 troops of the People's Army of Vietnam (PAVN) and the National Front for the Liberation of South Vietnam (NLF, also known as Viet Cong) who were ensconced in the eastern border regions of Cambodia. Cambodia's official neutrality and military weakness made its territory effectively a safe zone where Vietnamese communist forces could establish bases for operations over the border. With the US shifting toward a policy of Vietnamization and withdrawal, the US sought to shore up the South Vietnamese government's security by eliminating the cross-border threat.
A change in the Cambodian government allowed a window of opportunity for the destruction of the base areas in 1970 when Prince Norodom Sihanouk was deposed and replaced by pro-US General Lon Nol. Allied military operations failed to eliminate many communist troops or to capture their elusive headquarters, known as the Central Office for South Vietnam (COSVN), but the haul of captured material in Cambodia prompted claims of success.
In the III Corps Tactical Zone, Operation Toan Thang 44 (Operation Bold Lancer), was conducted by the 1st and 2nd Brigades of the U.S. 25th Infantry Division between 6 May and 30 June. The targets of the operation were Base Areas 353, 354, and 707 located north and northeast of Tay Ninh, South Vietnam. Once again, a hunt for COSVN units was conducted, this time around the Cambodian town of Memot and, once again, the search was futile. During its operations, the 25th Infantry killed 1,017 PAVN and NLF troops while losing 119 of its own men killed.
Another main objective was to locate and destroy COSVN. Central Office for South Vietnam (abbreviated COSVN /'k??zv?n/; Vietnamese: Van pḥng Trung uong C?c mi?n Nam), officially known as the Central Executive Committee of the People's Revolutionary Party from 1962 until its dissolution in 1976, was the American term for the North Vietnamese political and military headquarters inside South Vietnam during the Vietnam War. It was envisaged as being in overall command of the communist effort in the southern half of the Republic of Vietnam (South Vietnam), which included the efforts of both People's Army of Vietnam (PAVN), the Viet Cong, and the People's Revolutionary Party.
The campaign was touted a success, with about a quarter of the opposition destroyed (12,354 KIA'd and 1,177 captured) the rest having escaped further into Cambodia. Losses for the US forces, 338 KIA'd and 809 for the ARVN's. On the bright side, stores of weapons, ammunition and food supplies was uncovered and turned over to the Cambodian and ARVN forces that were located in staging areas within the areas of operations. The CIA disputes the figures used to account for enemy losses as including civilian casualties.