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Vietnam War Articles
The Green Beret Affair: A Factual Review
The "Green Beret Affair"
America's Paradoxical Trinity
The Cambodian Incursion
Dien Bien Phu: A Battle Assessment
The Effects of Vietnamization
The Battle for Hue
Dien Bien Phu 50 Years Later
The Wild Weasels
Role of Airpower in Vietnam

Jeremiah Boenisch Articles
The Cambodian Incursion

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Recommended Reading

Incursion: From America's Chokehold on the Nva Lifelines to the Sacking of the Cambodian Sanctuaries

Vietnam Battle Chronology: U.S. Army and Marine Corps Combat Operations, 1965-1973

The Vietnam War Almanac

Jeremiah Boenisch Books

Continuity Management

The Cambodian Incursion: A Hard Line for Change
The Cambodian Incursion: A Hard Line for Change
by Jeremiah S. Boenisch


On 1 May 1970, United States and South Vietnamese units launched a ground and air offensive into neutral Cambodia to eliminate North Vietnamese sanctuaries used for frequent raids into South Vietnam. Dubbed the Cambodian Incursion by President Nixon, the U.S. ground operation took place over a 60-day period from 1 May to 29 June and was overlapped by Allied air strikes and a 75 day South Vietnamese incursion.[1] By combining the efforts of the South Vietnamese, devastating air power, and army ground forces, the Allied Forces overwhelmed enemy positions and supply points resulting in thousands of enemy killed and an unprecedented recovery of enemy materiel. Although the incursion is sometimes portrayed as a strategic failure, it was not. This paper will illustrate that the campaign, though unpopular, was actually the key event necessary for severing the enemy's lines of communications and logistics in Cambodia, aiding the successful withdrawal program, saving U.S. credibility, and showing the success of Vietnamization.

Strategic Setting

To set the stage for this operation, it is necessary to understand the relevant events leading up to the Cambodian Incursion, plus the strategic and political situation in the Spring of 1970. In 1969, the peace talks between the U.S. and the North Vietnamese government were stalled in Paris and the Nixon administration's hopes of reaching a quick end to hostilities had faltered. Henry Kissinger's secret visits with North Vietnamese leaders to attempt to establish a negotiated peace had been deadlocked by the intransigence of an unbending foe. The North Vietnamese were demanding, "America's unconditional withdrawal coupled with the overthrow of Nguyen Van Thieu's government in Saigon."[2] This was an untenable position for President Nixon since he believed that a unilateral withdrawal of American Forces from Vietnam would not only be destructive and demoralizing to the South Vietnamese, but would damage U.S. credibility around the world. The President believed, "If, when the chips are down, the most powerful nation, The United States of America, acts like a pitiful, helpless giant, the forces of totalitarianism and anarchy will threaten free nations and free institutions throughout the world."[3] Faced with the dilemma of how to withdraw U.S. forces while still giving the South Vietnamese a fighting chance to defend themselves, Nixon chose a broad U.S. policy designed to bolster the South Vietnamese with substantial American aid and training called Vietnamization.

The North Vietnamese Army (NVA) and Viet Cong (VC) strategy leading up to the incursion had been to maintain pressure on the Americans while negotiations were continuing in Paris. Led by Gen. Vo Nguyen Giap, the northern leaders wanted and needed success on the battlefield to show that the American goal of Vietnamization was not going to save South Vietnam. Only three weeks after Nixon was inaugurated the NVA launched a campaign designed to strike at American positions throughout South Vietnam. Over the ensuing months NVA forces would kill an average of 1000 Americans a month.[4]

In direct response, Nixon authorized secret air strikes against NVA outposts in Cambodia and dropped a half million tons of bombs in a counter NVA campaign called "Menu."[5] At the same time U.S. and Army of the Republic of Vietnam (ARVN) troops advanced to the Cambodia border in an effort to push the NVA and VC out of South Vietnam. Having been pushed back, NVA troops continued to use the Cambodian border and its neutrality for frequent attacks and as sanctuary from ground attacks.

During this same time the Cambodian Prime Minister, Lon Nol, ousted longtime Cambodian leader, Prince Norodom Sihanouk. From the American perspective, the coup was welcome because Prince Sihanouk had secretly allowed the NVA use of his country for logistical bases and infiltration routes into South Vietnam (Reference Appendix B and C).[6] However, an unsympathetic Lon Nol would pursue both the NVA and the Cambodian insurgents (the Khmer Rouge); touching off a messy civil war. Without adequate forces to defeat or defend his country Lon Nol called out to the international community for assistance.[7] Thus, the U.S. was presented with an opportunity to move into the Cambodian strongholds.

On 20 April 1970, eleven days prior to the Cambodian Incursion, President Nixon addressed the nation on the situation in Vietnam and announced the withdrawal of 150,000 American troops. He stated, "We have now reached a point where we can move…to a longer range program for the replacement of Americans by South Vietnamese."[8] In what seemed to be a taunting response to Mr. Nixon's speech, the days leading up to the incursion would be marked by an escalation of NVA hostilities in Cambodia.

Responding to this apparent provocation, Nixon authorized the Commander of American forces, General Creighton Abrams, to execute an incursion into Cambodia. Beyond eliminating the communist sanctuaries, the President's objectives for the campaign were outlined in his speech on 30 April 1970:

1) Show the success of Vietnamization
2) Buy time for the success of the withdrawal program
3) Uphold U.S. ideals and credibility[9]

General Abrams' operational plan to accomplish these objectives was simple: destroy the sanctuaries and you remove the ability of the enemy "to raise or lower the level of combat at will."[10] His method was to use air strikes followed by South Vietnamese (led by Lt. General Do Cao Tri) and U.S. ground forces in an attack against sanctuaries and the major port facility, Sihanoukville (Reference Appendix D for operations into Cambodia). The enemy forces in the region included the 5th and 7th NVA Divisions as well as the 5th Viet Cong Division.[11]

Abrams' strike forces would include: U.S. Air Force B-52s, F-4s, RF-4s, O-2s, etc.; U.S. Army's 1st Cavalry Division, 4th Infantry Division, 25th Infantry Division, 9th Infantry Division, 11th Armored Cavalry Regiment, 199th Light Infantry Brigade; South Vietnam's 5th, 9th, 21st, 22d and 23d ARVN infantry divisions, 1st ARVN Airborne Division and 2d ARVN Armored Brigade.[12]

The Time for Payback

The time for payback had come. North Vietnamese and Viet Cong forces had been using Cambodia and its neutrality for over five years to capture and kill American and South Vietnamese troops. The U.S. had respected the neutrality of Cambodia but had paid a heavy price for doing so. American soldiers lamented that, "We had lost many men in combat assaults near the Cambodian border while the gooks would go back into Cambodia, sit there and laugh at us."[13] Coupled with the payback was the fact that large amounts of supplies and several divisions of NVA and VC were in the area in preparing for massive strikes against South Vietnam that would start by taking down Lon Nol and the Cambodian government (Reference enemy estimates in Appendix D).[14]

An enthusiastic General Abrams would commence the operation to clean out the sanctuaries on 24 April 1970 with tactical air strikes designed to soften NVA targets.[15] Five days later, the South Vietnamese ground forces moved into action, followed by the Americans two days later. The primary operational objective of the Allied forces was to conduct "search and destroy operations to find and eliminate NVA and VC sanctuaries in Cambodia and the troops defending them."[16] The Campaign would span 75 days and have 12 operations of which only 2 would be led by U.S. ground forces (Reference Appendix D for operations).[17]

The Objectives

Cambodia could no longer be used as a safe haven for the NVA and VC. Allied forces had pushed the enemy out of their strongholds along the border and the port city of Sihanoukville with relative ease while simultaneously capturing an incredible amount of materiel (Reference Appendix A for map). More importantly their tactical and operational efforts achieved most of President Nixon's strategic objectives for the campaign. To better judge the impact of the Cambodian Incursion it is helpful to investigate the tactical and operational effects of the campaign to determine if they met the strategic objectives.

The first objective of the campaign was to show success of the Vietnamization Program. A major campaign with ARVN forces, taking a major role, presented just such an opportunity. From the outset the campaign plan would maximize the use of South Vietnamese forces which according to Nixon, "would be a major boost to their morale as well as...demonstrate the success of Vietnamization."[18] With an 8,700 man force, South Vietnamese troops would officially start their incursion with Operation Toan Tang 42 (Total Victory) on 29 April 1970.[19] This operation, into the Parrots Beak area, would be a difficult one against fortified enemy positions (Reference Appendix F for map). U.S. commanders would watch closely to judge the performance of the South Vietnamese. Some had argued that they did not fight well and could not survive without American support. Yet after its first major test, the South Vietnamese forces would engage in hand to hand combat, out kill, and otherwise outperform the enemy.[20] Before the Cambodian Incursion was concluded ARVN forces would lead 10 of the remaining 12 operations. The South Vietnamese Army's performance in the operation seemed to indicate that the Vietnamization of the war was a success. As Samuel Lipsman, the author of The Vietnam Experience: Fighting for Time, stated, "If the Parrots Beak was a test of the feasibility of America's Vietnamization policy, the ARVN's aggressive mobility and thorough searching was an encouraging sign."[21]

The second objective, to buy time for the success of the withdrawal program, was met by using overwhelming force against the sanctuaries. Before going into Cambodia, American and South Vietnamese forces expected to encounter fierce resistance. Intel had estimated that at least three divisions of the enemy awaited the invasion force.[22] However, in most cases the enemy had withdrawn under fierce bombing and the presence of Allied forces massing along the border. In fact, one of the primary targets Mr. Nixon mentioned in his 29 April 1970 speech, the Central Office for South Vietnam (COSVN) headquarters, had to move west of the Mekong River for security (Reference Appendix G for map).[23] With its radio networks unable to operate, the command and control of enemy forces broke down causing significant confusion to subordinate enemy forces.[24]

The Allied air forces, in many cases, were the principal antagonists in creating this chaos for the enemy. They would fly over 14,000 attack sorties that obliterated supply caches and enemy positions.[25] U.S. B-52s, based out of Guam, would fly 653 sorties in 6 of the 12 ground operations.[26] The planes outfitted for carrying dozens of conventional 750lb bombs, were controlled by Strategic Air Command, but General Abrams could call up to 60 a day for his use.[27]

In conjunction with the air forces were four U.S. Army Divisions (1st, 4th, 9th, 25th) who would join in operation Toan Thang 43 and 44 (Total Victory) to hit areas in Fish Hook (Reference Appendix G for map) and other sanctuaries. They delivered a knockout punch to enemy forces in the region. As one General put it, "This Cambodian operation is pure blitzkrieg, like something from World War II Panzer Division book of tactics."[28]

The combined tactical and operational effect was truly remarkable. In the span of 75 days the allied missions had resulted in 11, 562 enemy killed and the capture of an extraordinary amount of materiel (Reference Appendix I).[29] To put it in perspective, the allied forces captured enough armament to outfit 54 battalions of 450 men each, enough ammunition to sustain the NVA army for a year, and enough rice to feed the enemy forces for 6 months (Reference Appendices H and I).[30] Headquarters Military Assistance Command Vietnam (MACV) estimated, "It would take the enemy a minimum of 9 months to reorganize his logistics and…up to 6 months to replace the men lost."[31]

It has been speculated that the incursion could have been decisive, if given the freedom of maneuverability and the time to pursue NVA forces. However, in response to pressure from the media, the tragic Kent State shootings, and a public outcry, the President put an operational restriction on the duration and penetration of the U.S. forces. Although this hampered U.S. forces, the outcome of the Cambodian Incursion would be seen as one of the most successful campaigns in the Vietnam War.

By the end of the campaign Allied forces would disrupt a planned NVA offensive, buy time needed for Vietnamization, and enable the continuation of the withdrawal of U.S. forces. Within seven months of the Cambodian Incursion over 115,000 troops would come home.[32] For those still stationed along the Cambodian border things would be quiet for many months to come.

In order to appreciate the third objective of upholding U.S. ideals and credibility, it is meaningful to look at the Cambodian Incursion in the context of its influence and outcome. Within three years of the campaign Nixon and Kissinger extracted the United States from the protracted Vietnam War. They would be featured for their success as men of the year on the front cover of Time Magazine. The caption would read "Triumph and Trial" underscoring the long and difficult struggle to achieve peace in Vietnam.[33] Although not readily apparent at the time of the Cambodian Incursion, their success began by taking a hard line with the enemy by backing rhetoric with force. The Incursion was not an easy choice for the administration, but it represented an opportunity to reestablish the credibility of the United States and achieve Nixon's goal to leave Vietnam with honor.

It wasn't an easy road and the fruits of the Cambodian Incursion were not readily apparent during or shortly after the campaign. The credibility of the U.S. would take a significant hit and a secret public opinion poll conducted in Europe and Asia would confirm a drop in American prestige.[34] Many in the press saw the move into Cambodia as a violation of that nation's neutrality and an expansion of the war. On college campuses protests and riots would break out in response to the Incursion and at Kent State University (on 4 May 1970) four students would be killed and nine wounded by National Guard troops trying to break up demonstrations.[35]

The events surrounding the Cambodian Incursion looked and felt terrible to many Americans. It was a miserable time in U.S. history that many want to forget. However, through the smoke of emotion it is evident that President Nixon had a clear plan to reestablish the credibility of the United States and he made it clear to his commanders, his administration, and ultimately the world. In his speeches on 20 and 29 April 1970, Nixon defended his position upholding the ideals of the U.S. making it clear that he would not tolerate an enemy that would "humiliate and defeat us."[36] The enemy would test the President's resolve by increasing their attacks and Mr. Nixon would make good on his promise to respond with force.

The path was set and the President was taking responsibility. In his speech on 29 April he put his presidency on the line stating, "Whether I may be a one-term President is insignificant compared to whether by our failure to act in this crisis the U.S. proves itself to be unworthy to lead the forces of freedom in this critical period in world history."[37] As evidenced in his memoirs and speeches, Nixon believed that the Cambodian Incursion was the best way to get Americans out of Vietnam while upholding their honor. He had grown tired of a non-capitulating enemy at the negotiating table and of an enemy who played a cat and mouse game from a neutral country. His commanders on the ground supported this notion and believed that the campaign would have a tremendous effect on the morale of the troops as well as buy the necessary time to get out. The world would come to understand that this President wasn't afraid to make the tough decisions.

With those tough decisions Nixon hoped to bring the enemy back to the negotiating table. The results were difficult to assess after the campaign because the enemy didn't immediately capitulate. However, two years later the enemy would concede to American terms at the Paris Peace talks. Henry Kissinger cited the Cambodian Incursion as a primary contributor to bringing the North Vietnamese back to the conference table. He believed that "a combination of factors brought Hanoi to the point of accepting U.S terms…including the attack on the Cambodian Sanctuaries in 1970."[38]

The conflict between the peace movement and the President's administration would continue unabated until the end of the war. However, the path to peace and retaining U.S. credibility started by both destroying the enemies ability to fight from a neutral country and by a outspoken President who wanted to leave Vietnam with honor.


In conclusion, the success of the Cambodian campaign was the result of more than just good tactics. It was a combination of tactical and operational effects that brought important strategic results. The well executed campaign would use a devastating combination of air and ground forces to overwhelm the Viet Cong and the North Vietnamese Army, who had long used the neutrality of Cambodia as a safe haven. The Allied forces would achieve stunning victories by killing thousands, crippling logistics and otherwise affecting the enemy's ability to strike for many months to come. In favor of a hard line approach, President Nixon used the campaign to take a stand against a non-capitulating enemy. He had made his promise to the American people to leave Vietnam, but he would not leave without honor, nor would he make peace at any price. Instead, the President used the tactical and operational capacity available to him to establish a hard line with the enemy that would have a positive effect on the strategic outcome of the campaign. His decision impacted the way the enemy would view the U.S. and the way the war was fought in the future. The combination of the President's leadership and the success of the Cambodian Incursion helped to reestablish U.S. credibility, allowed for a successful withdrawal program and demonstrated the success of Vietnamization.

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Show Footnotes and Bibliography

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Copyright © 2006 Jeremiah S. Boenisch.

Written by Jeremiah S. Boenisch.

About the author:
Jeremiah S. Boenisch is an officer in the US Air Force currently assigned to the Marine Corp Command and Staff College. He earned his B.S. degree in Environmental Science and his B.S. degree in Political Science with minors in Environmental Health and Aeronautical Science from Oregon State University and his M.A. in Organizational Management from The George Washington University. Jeremiah is a co-author of Continuity Management, John Wiley and Sons, 2002.

Published online: 12/16/2006.

* Views expressed by contributors are their own and do not necessarily represent those of MHO.
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