CHAPTER 3

The Cambodia Invasion and Continued Redeployment Planning, April-July 1970

The War Spreads Into Cambodia-Redeployment Planning Accelerates: Keystone Robin Alpha Plans for the 3d MAB

The War Spreads into Cambodia

While the day-to-day war absorbed the full attention of most of the officers and men of III MAF, commanders and staff officers at MAF, division, and wing headquarters, besides directing current operations, had to keep track of developments elsewhere in the war and plan for events and contingencies as much as a year away. During the spring and early summer of 1970, the attention of these officers centered on three problems: the probable effects in 1 Corps of the allied invasion of Cambodia; plans and preparations for major new troop withdrawals; and the organization of the Marine air and ground forces that would be left in Vietnam after most of III MAF redeployed.

During the spring, the allies opened a new theater of war in Cambodia, South Vietnam's neighbor to the west- They acted in response to the collapse of Cambodia's long maintained but increasingly precarious neutrality. In March, the Cambodian premier. General Lon Nol, led a successful coup d'etat against the country's ruler, Prince Norodom Sihanouk. When the new government tried to expel the North Vietnamese and Viet Cong from the extensive base areas they had built up on the Cambodian-Vietnamese border, righting broke out between government troops and the NVA and VC, who were assisted by the growing forces of the Communist-inspired Khmer Rouge movement.

The American and South Vietnamese high commands had long wanted to strike at the border base areas only 35 miles from Saigon. Taking advantage of the Cambodian upheaval, the allies, beginning on 29 April, sent division and brigade-size task forces slashing into what had been enemy sanctuaries. During May, the U.S. Army and the ARVN carried on search and destroy operations in a dozen base areas adjoining the II, III, and IV Corps areas of South Vietnam. A U.S.-Vietnamese naval task force* commanded by Rear Admiral Herbert S. Matthews, Deputy Commander Naval Forces Vietnam (ComNavForV) at the same time swept up the Mekong River to open a supply line to Cambodia's besieged capital, Pnomh Penh. The fighting continued through June. At the end of that month, in accord with a promise by President Nixon that this would be a limited attack for the sole purpose of preventing enemy offensives against South Vietnam, all U.S. ground troops left Cambodia. ARVN units continued to range the base areas, however, and American arms and supplies flowed to the ill-trained and hard-pressed forces of General Lon Nol.

While bitterly controversial in American politics, the invasion of Cambodia seriously weakened the enemy. By early July, MACV estimated that the Communists had lost as a result of the invasion 10, 000 men, over 22, 000 weapons, 1, 700 tons of munitions, and 6, 800 tons of rice. According to allied intelligence, the attack had forced COSVN Headquarters to displace, causing the enemy to lose command and control of many of their units in South Vietnam. Destruction of the base areas combined with Lon Nol's crackdown on pro-Communist elements in Cambodia had left the NVA and VC in southern South Vietnam temporarily without sufficient supplies for a major offensive. Replenishment of the Cambodian caches with material brought down the Ho Chi Minh Trail through Laos would require much time and the commitment to supply operations of thousands of additional troops and laborers. Further weakening their position, the NVA now had to use their own soldiers to control a large portion of northeastern Cambodia as well as to support Khmer Rouge units.1

The invasion of Cambodia had little immediate impact on conditions in I Corps. Of the allied forces there, only Marine aviation units participated in the invasion. During May and June, jets from MAGs-11 and -13 flew 26 missions over Cambodia, most of them in support of the U.S. Army's 4th Division and the ARVN 22d Division as they swept an enemy base area about 40 miles west of Pleiku. Other Marines, advisors to the Vietnamese Marine brigades, accompanied the Mekong River task force.**2

* According to Admiral Matthews, the supply line up the Mekong River to Pnomh Penh remained open until January 1971 when heavy interdiction by the VC necessitated a second Vietnamese task force 10 reopen it. RAdm Herbert S. Matthews, Comments on draft ms, 3Mar83 (Vietnam Comment Files).

**for details of air operations, see Chapter 15. and for the Marine advisory role see Chapter 21.