The history of Cambodia is intricately linked to both Laos and Vietnam. In modern times Cambodia was part of the French Colonial empire, taken over by the Japanese during World War II. After the war, the French returned but granted Cambodia independence in 1953, with Prince Norodom Sihanouk as Chief of State in the capital at Phnom Penh. The Geneva Accords of 1954, that ended the First Indochina War with the French, divided Vietnam at the 17th parallel and also confirmed the status of Cambodia and Laos as independent states.
Engineers clear mines from a trail in Cambodia, 1970.
The U.S. and Cambodian Chief of State Prince Norodom Sihanouk cooperated in the development of a Cambodian military, both intending for Cambodia to be an independent buffer state, free of Communist insurgency. A U.S. Military Assistance and Advisory Group for Cambodia was established and funded with over $85 million to aid in the training of the Cambodian Army. Unlike Laos, there was no indigenous element in Cambodia trying to establish a Communist government but North Vietnam threatened the border regions and used them in the Ho Chi Minh Trail complex.
In 1958, Cambodia opened diplomatic channels to Communist China, increasing doubts about the country's reliability as a U.S. ally. By 1960 the NVA were making overt use of Cambodian territory for logistical support of their operations in South Vietnam. Although Sihanouk continued to accept U.S. aid, he feared Cambodian involvement in Vietnam and did not use his Army to interfere with the NVA activity even when it was publicly known. On the other hand, when U.S. or S. Vietnamese troops chased NVA/VC across the Cambodian border, such incursions were protested as violations of the 1954 Geneva Accords. By 1965, Sihanouk was convinced the CIA was fomenting plots to oust him. He severed relations with the U.S., all advisors were ejected, and Cambodia began accepting aid from Communist countries.
Sihanouk soon had reasons to regret closer ties to the Communists. In 1967 a Communist-backed peasant revolt created a Communist insurgency called the Khmer Rouge under Pol Pot. These developments were reason enough for the U.S. to dispatch Special Forces teams into Cambodia on "Daniel Boone" missions to discover and monitor NVA/VC base areas along the border. By late 1968 the North Vietnamese were moving most of their supplies by a sophisticated network of truck, pipeline, and river barge facilities that terminated at depots within and adjacent to South Vietnam. As the U.S. policy of Vietnamization took hold, the Communist forces had less support within South Vietnam and came to rely on the Ho Chi Minh Trail and cross-border sanctuaries. The neutralization of the Cambodian bases became a more urgent issue since they were key to the NVA/VC strength that the S. Vietnamese would be resisting alone. The bulk of the Communist installations were located in the "fishhook" and "parrot’s beak" salients, the latter only about 35 miles from Saigon. From the relative security of these sanctuaries, the North Vietnamese and Viet Cong forces were able to mount periodic forays across the border into the III Corps area of South Vietnam.
U.S. Bombing Raids in Cambodia
U.S. President Richard M. Nixon during the press conference on Vietnam and Cambodia, 30 April 1970.
In March 1969, in violation of the Geneva Accords and without informing Congress, the Nixon administration began the secret B-52 bombing of North Vietnam's Cambodian bases, the "Menu Series" of raids. Sihanouk did not object to these raids since he had his own worries with the rise of Communist power within Cambodia. The B-52s flew 3,630 sorties over Cambodia during Menu Series using various deceptions and false reports to maintain the fiction that only S. Vietnam was being bombed.
Although the raids were effective in suppressing activity that affected S. Vietnam, the fleeing Communist forces clashed with the Cambodian Army as they retreated from border regions. By that time an estimated 35,000 to 60,000 Communist troops were in Cambodia, located principally in eastern Cambodia adjacent to South Vietnam. The resulting turmoil culminated in a military coup that deposed Sihanouk and brought pro-U.S. General Lon Nol to power in Cambodia on 18 March 1970. It has been suggested that the U.S. backed the coup, but there is no evidence of U.S. intervention.
The April 1970 Cambodian Incursion
The rise of Lon Nol, a U.S. ally, was highly destabilizing. Lon Nol ordered the NVA out of the country when they rejected a compromise proposal, but they refused and civil war broke out between Lon Nol's government and the Communist forces, both NVA and Khmer Rouge. The new Cambodian government denied use of the port of Sihanoukville to the Communists, meaning that their logistics now depended on the long overland route from North Vietnam south through Laos to their sanctuaries. The Communists immediately moved to ensure the safety of this route by consolidating and expanding their separate pockets of strength throughout eastern Cambodia. The 600 mile border between Cambodia and S. Vietnam was becoming one large Communist base. In addition, such a massive presence of Communist forces in Cambodia threatened the existence of the Lon Nol regime as the civil war went on. In early April 1970, the Cambodian government sought military assistance from the United States and South Vietnam. In the last two weeks of April, the U.S. supported ARVN in a series of successful small operations in Cambodia, without U.S. troops crossing the border. The success of those raids encouraged larger action.
Feeling forced to act, both to support Lon Nol and to reduce the threat to Vietnamization, on 29 April 1970, with U.S. air and logistic support, South Vietnamese forces attacked Communist forces just across the border in the "parrot’s beak" area of Cambodia. On 1 May, US and ARVN forces entered the "fishhook" region. The Cambodian Incursion, named Operation Toan Thang 43, was led by the US 1st Cavalry Division, 11th Armored Cavalry Regiment, and 25th Infantry Division, along with the ARVN units. In both "fishhook" and "parrot’s beak," the main NVA forces were warned by the earlier raids, and withdrew without decisive contact. Large quantities of supplies and major base camp areas were captured and Communist logistics were disrupted, more so than had been anticipated.
On 9 May, a fifty-ship combined U.S.-Vietnamese naval force under Sealords entered Cambodia with the objective of clearing the Mekong River all the way to Phnom Penh. The force, augmented by air cover, destroyed all Communist craft that were met. South Vietnamese forces reached Phnom Penh while the U.S. units were politically constrained to an area south of the Neak Luong transit point which was successfully assaulted and cleared. S. Vietnamese units remained in the area, permanently disrupting Communist logistics and base camps.
Pres. Nixon placed Gen. Abrams under strict rules of engagement designed to keep casualties low and to limit the scope of the operation. A line was drawn 19 miles inside Cambodia and U.S. forces could not advance past it, allowing NVA units who reached the limit to escape unscathed. A time limit was also imposed -- all U.S. forces out of Cambodia by 30 June, publicly announced by Pres. Nixon on 7 May. These limits were strictly observed. South Vietnamese forces continued the fight and in fact remained in Cambodia for the next 18 months.
By the end of June U.S. and ARVN forces in Cambodia had captured or destroyed almost ten thousand tons of materiel and food. In terms of enemy needs this amount was enough rice to feed more than 25,000 troops a full ration for an entire year; individual weapons to equip 55 full-strength battalions; crew-served weapons to equip 33 full battalions; and mortar, rocket, and recoilless rifle ammunition for more than 9,000 average attacks. In all, 11,362 enemy soldiers were killed and over 2,000 captured. ARVN units involved in Cambodia fought well and were often led well. ARVN units returned to S. Vietnam to resume pacification of the Mekong Delta, a goal which had suddenly come much closer to realization. In general in S. Vietnam, large VC and NVA attacks almost ceased for over a year because of the setbacks imposed on them in Cambodia.
In the United States, the aftermath of the 1970 Cambodian Incursion was severely negative. War protests reached new peaks over fears that Nixon was widening the war instead of winding it down. The tragic shooting of students at Kent State University in Ohio occurred 4 May 1970 during a protest over Cambodia. In Cambodia itself, the retreating NVA conquered much of the northeastern sector of the country and turned it over to the Khmer Rouge, thereby strengthening the Communist insurgency.
Operation Cuu Lorry 44-02 January 1971
One more S. Vietnamese operation in Cambodia was conducted in 1971, staged because the North Vietnamese had cut Route 4, the only supply road in Cambodia between Phnom Penh, the capital, and the port of Kampong Som. The Cambodian government requested South Vietnamese assistance in reopening the route. The penetration into Cambodia, the deepest of the war, was politically sensitive so the operation, although successful, has not been widely publicized.
Operation Cuu Lorry 44-02 began on 13 January 1971, as the 4th Armor Brigade with the 12th and 16th Armored Cavalry Regiments, three Ranger battalions, an artillery battalion, and an engineer group, moved 300 kilometers from Can Tho to Ha Tien in fourteen hours. For the next two days, the brigade pushed north along Routes 3 and 4 performing very well as they encountered ambushes and other attacks along the way. On 17 January Cambodian forces, with Vietnamese Marine Corps support, fought to the outskirts of the Pich Nil Pass and secured it, while the armor brigade secured Route 4 as far north as Route 18. After helping the Cambodians set up strongpoints, the 4th Armor Brigade withdrew toward South Vietnam, arriving by 25 January.
Final Stages of U.S. Involvement in Cambodia
After the Paris Peace Accords were signed in January 1973, ending the U.S. involvement in Vietnam, the Lon Nol government requested U.S. aid to resist increased attacks by the Cambodian Communists. Ground troops were out of the question, but Pres. Nixon was not prepared to write off Cambodia. Arms, ammunition, and essential commodities were sent through airlift and Mekong River convoy. Arc Light B-52s from Guam were authorized to bomb Khmer Rouge strongholds throughout Southeast Cambodia -- the Air Force dropped an estimated 140,000 tons of ordnance from March though May of 1973. When the Communists launched a massive offensive on 30 June, in order to isolate the capital from the sea, President Nixon authorized a step-up in American bombing to break the impact of that offensive. Fighter bombers from Thailand conducted over 200 missions a day, and B-52s from Thailand and Guam flew some 40 missions a day over Cambodia.
President Nixon, under pressure from Congress and weakened by the Watergate scandal, ordered a halt to US military action in Southeast Asia after 15 August 1973, as required by the 19 June 1973 Case-Church Amendment. By then, the air strikes had dropped an unprecedented tonnage of bombs and forced the Khmer Rouge to retreat. Cambodian casualties, many innocent civilians, were estimated as high as 100,000 and the Cambodian economy was permanently disrupted. Lon Nol was able to hang on in Phnom Penh, but the bombing devastation turned the country into a basket case. It took the Khmer Rouge until early 1975 to recover enough strength to try again to take Phnom Penh, this time confident that the U.S. would not intervene.
On 1 April 1975, President Lon Nol resigned and left the country. On 12 April 1975 the last American operation in Cambodia, Eagle Pull, was the helicopter evacuation rescue of 82 U.S., 159 Cambodian, and 35 other nationals as Communist forces closed on the capital city. The Communists under Pol Pot took over Phnom Penh and began a killing spree against all known and suspected enemies. At least 1.5 million Cambodians died from execution, forced hardships, or starvation during the Khmer Rouge regime.
USS Mayaguez Postscript
On 11 May 1975, Khmer Rouge forces armed with AK-47s boarded and captured the U.S. Merchant Ship, Mayaguez in waters off Cambodia and Vietnam. The ship was taken to enforced anchorage off Koh Tang, a tiny island in Cambodian coastal waters. U.S. President Ford wanted a forceful response to the act of piracy, signalling the world that the American withdrawal from Vietnam did not mean U.S. interests would not be defended. On 15 May, a Marine Task Force under the command of Colonel John M. Johnson launched an assault on Koh Tang, recovering the Mayaguez and her crew.
It was a costly effort. During staging for the rescue mission, a helicopter from the USAF 56th Security Police Squadron crashed, killing 18 Security Policemen and 5 crew members aboard. In the Marine operation, an additional fifteen U.S. personnel were killed and fifty wounded.