Week of May 3

Week of May 3

The end of April and the beginning of May 1970 was a volatile time in Vietnam as well as the United States. On April 28, 1970—despite the misgivings of Secretary of Defense Laird and Secretary of State Rogers—President Richard Nixon gave the final assent for United States and South Vietnamese forces to make a temporary incursion into Cambodia. The forces involved included approximately 30,000 U.S. troops and 50,000 South Vietnamese troops. It became one of the most significant operations of the war and the largest since 1967. To minimize the expected public backlash in the United States, Nixon insisted that no American troops be allowed to penetrate more than 19 miles into Cambodia, and that all of them must return to South Vietnamese territory by June 30.

The incursion had multiple objectives. Primarily, the U.S. and South Vietnam hoped to disrupt and destroy supplies and bases along the Ho Chi Minh Trail in eastern Cambodia, from where the bulk of Communist arms and troops infiltrated South Vietnam. But other goals included relieving Communist military pressure on Phnom Penh and the pro-U.S. Lon Nol regime in Cambodia, increasing Washington’s leverage in ceasefire negotiations with Hanoi, and demonstrating the ostensible progress of Vietnamization and the competence of the South Vietnamese armed forces.

Finally, Nixon hoped that with luck, allied forces could locate and destroy the supposed headquarters of the Viet Cong insurgency, known as the “Central Office for South Vietnam” (COSVN). Allied intelligence agents believed COSVN was a large headquarters element and a communications and logistics hub, possibly staffed by hundreds of personnel. They traced its location to a southeastern part of Cambodia known as the “Fishhook” region just northwest of Saigon. The Nixon administration and MACV believed that finding and destroying COSVN would strike a critical blow to Hanoi’s ability to wage war in South Vietnam.

The Cambodian operation began with barrages of B-52 Stratofortress and ground artillery strikes on April 29. Then, U.S. and South Vietnamese forces crossed the border with a two-pronged assault into the “Fishhook” and the “Parrot’s Beak,” looking to destroy supply caches and to engage Viet Cong or North Vietnamese troops if encountered. They also made a series of airmobile assaults to cut off any possible Communist retreats, as well as a riverine incursion up the Mekong River.

As allied troops advanced, they encountered only sporadic resistance, mostly in the form of short firefights, harassing fire, small-scale ambushes, and snipers. They eventually found that the vast majority of Communist forces had already retreated westward, deeper into Cambodia, carrying what supplies they could while abandoning the rest. With no major enemy units to engage, the incursion became focused on locating these supply caches and destroying them. All U.S. troops complied with Nixon’s imposed deadline, crossing back into South Vietnam by June 29. Some South Vietnamese units remained in Cambodia for longer.

North Vietnamese supply bases and caches stretched along the entire length of the Ho Chi Minh Trail. One located by U.S. soldiers sprawled for well over a mile and consisted of at least 18 structures, including a mess hall, barracks, training facility, and hospital. In the final accounting after the incursion, MACV reported that the amount of supplies captured or destroyed in Cambodia was 10-times greater than the amount of supplies captured during all of the previous year. The list included, among other things, 18 million rounds of ammunition, 435 vehicles, and 700 tons of rice. The allies also claimed that 11,350 Communist troops had been killed and 2,300 had been captured or had defected.

The United States argued at the time that the Cambodia operation was a tremendous success and that, given the supplies captured and damage done to the Ho Chi Minh Trail logistics network, it bought at least another year for the Saigon government to prepare to defend itself after American withdrawal. But the incursion also resulted in losses. Casualties included 338 dead American servicemen and more than 1,500 wounded. The South Vietnamese lost 638 killed and more than 4,000 were wounded. The infamous COSVN headquarters was never found.

There was also a tremendous domestic political cost to the incursion for the White House. Despite Nixon’s assurances that the incursion was limited and temporary, it set off a political firestorm. Many people viewed it as an invasion of a new country and an escalation of the war that Nixon repeatedly promised was winding down. It prompted some members of Congress to draft legislation meant to check executive authority over the United States’ Vietnam policy.

In response to the news of the Cambodia operation, protests and sporadic violence broke out throughout the country and on over 400 college campuses, perhaps most memorably at Kent State University, Ohio (where National Guardsmen shot 13 protestors, killing four), and Jackson State College, Mississippi (where two more students were shot and killed by police), in May. The shootings at Kent State became a flash point that perhaps triggered as much outrage as the incursion itself, spurring the spread of more demonstrations. Protests continued to break out nationwide over the following weeks, reinvigorating the antiwar movement.

In Cambodia, the resulting movement of North Vietnamese troops deeper into the country to avoid the incursion inflamed simmering anti-Vietnamese sentiment, and a number of ethnic-Vietnamese Cambodians were murdered or had their property seized by the Cambodian government in the ensuing months.

In the immediate aftermath of the Cambodian incursion, observers largely agreed with the White House’s claims that it had been a military success. The administration argued—fairly persuasively at the time—that it not only critically damaged the Ho Chi Minh Trail network in Cambodia but also likely saved the Lon Nol government in Phnom Penh from a Communist takeover. Additionally, allied troops captured or destroyed a seemingly enormous amount of Communist supplies and arms, and Henry Kissinger argued that it had bought at least another year for the Saigon government to stabilize South Vietnam. This initial perception of success had important consequences.

While the incursion reinvigorated the antiwar movement and pushed new members of Congress to openly oppose the administration’s war policies, Nixon’s appeal to a “silent majority” again seemed to bear fruit. The president’s approval rating went from 53 percent in March, before the incursion, to 59 percent in May, after it had begun. The incursion also seemed to provide evidence that Vietnamization was progressing apace, since major units of the South Vietnamese Army reportedly performed well. Perhaps most importantly, the perceived success of the Cambodia operation heavily influenced the motivation for and the planning of a similar incursion into Laos in 1971, which turned into a military disaster from the allies’ perspective.

In the years after the Cambodian incursion, however, historians have mostly concluded that the operation’s seeming success was an illusion. Already by late 1970, analysts in the Pentagon determined that it had taken the North Vietnamese only about 75 days to replenish the supplies and men they had lost in the operation. The CIA’s analysis posited that estimates of Communist losses in excess of 11,000 men were likely much too high, and that disruptions to the Ho Chi Minh Trail were not permanent or critical. Most of the statistical measures of success used by the White House—the number of North Vietnamese casualties, the amount of captured supplies, etc.—later turned out to be exaggerations. Shortly after allied troops returned to South Vietnam, Communist forces reoccupied eastern Cambodia. Furthermore, in an effort to avoid open battle with American troops, the North Vietnamese moved deeper into Cambodia, actually resulting in Communist control of more territory.

The intelligence on COSVN had been mistaken. COSVN had been imagined as a major Communist headquarters, the destruction of which would be a crucial blow to Hanoi’s war aims. It turned out to be a small group of communicators, their equipment and trucks, and a minimal command staff, and it was easily moved deeper into Cambodia ahead of the arrival of allied troops. The ostensible progress of Vietnamization was also largely illusory, most scholars conclude, as the catastrophic Laos incursion of 1971 would reveal.

Some historians believe that the Cambodia operation may actually have hindered any momentum Vietnamization may have had by 1970. The incursion resulted in a flood of ethnic-Vietnamese refugees entering South Vietnam, who were fleeing Cambodia and persecution by both the Khmer Rouge and the Lon Nol government. This exodus increased the strain on an already-overburdened South Vietnamese security apparatus. Viet Cong attacks and infiltration of villages in South Vietnam measurably increased in 1970. The Khmer Rouge’s numbers increased as well. And the North Vietnamese Army had fully reoccupied all of the border regions within a month of the end of the incursion.

Within the United States, any political advantage Nixon gained from the Cambodian incursion was short-lived. The president’s frequent public assurances that America’s role in the war was winding down appeared to conflict with the strike into Cambodia, which increased distrust between the public and the administration. The perceived contradiction between the Nixon administration’s actions and its public statements encouraged insiders such as Daniel Ellsberg to leak classified information on the United States’ policies in Southeast Asia. Congress also became more assertive in putting forth legislation to check presidential authority and to limit the war going forward.

A small number of historians have argued that the Cambodian incursion was, in fact, successful in the sense that it was a “turning point” on the battlefield despite its political failings. They agree with official statistics for weapons captured and destroyed, intelligence gathered, and enemy casualties. They also believe that this campaign demonstrated that South Vietnamese forces had gained confidence, improved morale, and matured as an effective army given reports that a number of units performed bravely and well. Nixon’s only mistake, this group of writers has contended, was to limit the size and duration of the incursion, thereby preventing the campaign from being even more successful.

But most scholars disagree with this conclusion, responding that there is little credible evidence to support the notion that the incursion was a substantial military victory. Even in late 1970, they argue, available evidence showed that the North Vietnamese armed forces and the Viet Cong cadres were stronger after the incursion than before. In short, many informed observers in the early 1970s would have agreed with the conclusion reached by the majority of scholars in more recent years: that while the operation surely disrupted and delayed Hanoi’s plans for winning the war, only permanent occupation of Cambodia by U.S. troops could have made this achievement lasting. Given the intensity of the domestic backlash, such an occupation was always politically impossible. As former Assistant Secretary of State and author William P. Bundy puts it, aside from invading and permanently occupying Cambodia with thousands of American ground troops, it has never been clear exactly what the United States could have done to prevent the North Vietnamese and Khmer Rouge from controlling the Cambodian border regions.¹

¹Paul J. Scheips, The Role of Federal Military Forces in Domestic Disorders, 1945–1992 (Washington, D.C.: Center of Military History, United States Army, 2012), 401, 404; Richard A. Hunt, Melvin Laird and Nixon’s Quest for a Post-Vietnam Foreign Policy (Washington, D.C.: Historical Office, Office of the Secretary of Defense, 2014), 14; Spencer C. Tucker, ed., The Encyclopedia of the Vietnam War: A Political, Social, and Military History (2nd edition; Santa Barbara, CA: ABC-CLIO, 2011), 571–72; David L. Anderson, The Columbia Guide to the Vietnam War (New York: Columbia University Press, 2002), 131; George C. Herring, America’s Longest War: The United States and Vietnam, 1950–1975 (4th edition; New York and other cities: McGraw Hill, 2002), 293, 294; Stanley Karnow, Vietnam: A History (2nd revised edition; New York: Penguin, 1997), 626. William P. Bundy, A Tangled Web: The Making of Foreign Policy in the Nixon Presidency (New York: Hill and Wang, 1999), Chap. 3, Part 1; Gregory A. Daddis, Withdrawal: Reassessing America’s Final Years in Vietnam (New York: Oxford University Press, 2017), 123–33; Lien-Hang T. Nguyen, Hanoi’s War: An International History of the War for Peace in Vietnam (Chapel Hill, NC: University of North Caroline Press, 2012), 173–76; James H. Willbanks, ed., Vietnam War: The Essential Reference Guide (Santa Barbara, CA: ABC-CLIO, 2013), 23–29; Graham A. Cosmas, MACV: The Joint Command in the Years of Withdrawal, 1968–1973, United States Army in Vietnam (Washington, D.C.: Center of Military History, 2006), 279, 293, 296–98, 301–4 (for numbers see pp. 302–4). Spencer C. Tucker, ed., The Encyclopedia of the Vietnam War: A Political, Social, and Military History (2nd edition; Santa Barbara, CA: ABC-CLIO, 2011), 157–61; Edward J. Marolda, By Sea, Air, and Land: An Illustrated History of the U.S. Navy and the War in Southeast Asia (Washington, D.C.: Naval Historical Center, 1994), 284–85, 287; Thomas J. Cutler, Brown Water, Black Berets: Coastal and Riverine Warfare in Vietnam (Annapolis, MD: Naval Institute Press, 1988), 354–55. See, also, John M. Shaw, The Cambodian Campaign: The 1970 Offensive and America’s Vietnam War (Lawrence, KS: University Press of Kansas, 2005); Kenneth J. Conboy, The Cambodian Wars: Clashing Armies and CIA Covert Operations (Lawrence, KS: University Press of Kansas, 2013); Edward R. Drachman and Alan Shank, Presidents and Foreign Policy: Countdown to 10 Controversial Decisions (Albany, NY: State University of New York Press, 1997), 143–77; Ang Cheng Guan, Southeast Asia and the Vietnam War, Routledge Studies in the Modern History of Asia (London and New York: Routledge, 2010); Tran Dinh Tho, The Cambodian Incursion (Washington, D.C.: Center of Military History, 1979); Keith William Nolan, Into Cambodia: Spring Campaign, Summer Offensive, 1970 (Novato, CA: Presidio Press, 1990); Lewis Sorley, A Better War: The Unexamined Victories and Final Tragedy of America’s Last Years in Vietnam (New York: Harcourt, 1999), 208-16.

Map showing the location and routes followed in the Cambodian Incursion, May 1970. (U.S. Army Center of Military History)