Vietnamization was a policy of the Richard M. Nixon administration, to "expand, equip, and train South Vietnam's forces and assign to them an ever-increasing combat role, at the same time steadily reducing the number of U.S. combat troops." This referred to U.S. combat troops specifically in the ground combat role, but did not reject combat by U.S. air forces, as well as the support to South Vietnam, consistent with the policies of U.S. foreign military assistance organizations.
After Nixon's election in 1968, this became the policy of the United States. While it was a deliberate policy, the name was rather accidental. At a January 28, 1969, meeting of the National Security Council, GEN Andrew Goodpaster, deputy to GEN Creighton Abrams, commander of the Military Assistance Command, Vietnam, said the Army of the Republic of Viet Nam (ARVN) had been steadily improving, and the point at which the war could be "de-Americanized" was close. Melvin Laird, the Secretary of Defense, agreed with the point, but not with the language: "what we need is a term like 'Vietnamizing' to put the emphasis on the right issues." Nixon immediately liked Laird's word. 
Vietnamization fit into the broader Nixon Administration detente policy, in which the United States no longer regarded its fundamental stategy as containment of Communism, but a cooperative world order in which Nixon and his chief adviser Henry Kissinger were basically "realists" in world affairs, interested in the broader constellation of forces, and the biggest powers.  Nixon had ordered Kissinger to negotiate basic U.S.-Soviet policy between the heads of state via Kissinger and Dobrynin, with the agreements then transferred to diplomats for implementation. In like manner, Nixon opened high-level contact with China. U.S. relations with the Soviet Union and China were seen as far more important than the fate of South Vietnam, which certainly did not preclude South Vietnam maintaining its own independence.
Nixon said Vietnamization had two components. The first was "strengthening the armed force of the South Vietnamese in numbers, equipment, leadership and combat skills. The second component is the extension of the pacification program in South Vietnam." The first was achievable, but it would take time. For the U.S., it was trivial to have a U.S. helicopter pilot fly in support, but helicopter operations were too much part of ground operations to involve U.S. personnel. As observed by LTG Dave Palmer, to qualify an ARVN candidate for U.S. helicopter school, he first needed months of English language training to be able to follow the months-long training, and then additional field time to become proficient. In other words, adding new capabilities to the ARVN would often take two or more years. Palmer did not disagree that the first component, given time and resources, was achievable. "Pacification, the second component, presented the real challenge...it was benevolent government action in areas where the government should always have been benevolently active...doing both was necessary if Vietnamization were to work."
Nixon Administration analysis of options
Kissinger, earlier, had asked asked the Rand Corporation to provide a list of policy options, prepared by Daniel Ellsberg. On receiving the report, Kissinger and Schelling asked Ellsberg about the apparent absence of a victory option; Ellsberg said "I don't believe there is a win option in Vietnam." While Ellsberg eventually did send a withdrawal option, Kissinger would not circulate something that could be perceived as defeat. .
According to a record, prepared by Soviet Ambassador to the United States Anatoliy Dobrynin, of discussions between Dobrynin and Kissinger, the crux of the U.S. position, was progress still must be made at the Paris talks and, for domestic political reasons, Nixon “simply cannot wait a year for Hanoi to decide to take some new step and take a more flexible position.” Dobrynin expressed the Soviet position that the U.S.needed to stop trying to divide the Paris Peace Talks into two parts:
- discussion of military issues between the U.S. and the DRV
- resolution of political issues by placing them, "for all practical purposes, entirely
in the hands of Saigon, which does not want to resolve them and is unable to do so, since it is unable to soberly assess the situation and the alignment of forces in South Vietnam."Dobrynin, however, misunderstood the extent to which the U.S. was willing to apply military force not involving ground troops, culminating in Operation LINEBACKER II. 
Preparation under Johnson
Contrary to what some people suggested, Lyndon Johnson did not intend to keep escalating until his last day in office. Given his major interests were domestic, and that the war interfered with his domestic focus, he was eager to free his programs from the war — if he could find a way that he considered politically acceptable. Coincidentally, in 1967, Kissinger attended an Pugwash Conference of scientists interested in nuclear disarmament. Two participants approached Kissinger and offered a disavowable means of communicating American thoughts to the Communist leadership. In particular, Raymond Aubrac, an official of the World Health Organization, knew Ho Chi Minh and would carry a message to him.
After discussing the matter with Assistant Secretary of State William Bundy and Secretary of Defense Robert McNamara, a message was sent. After a ritualized condemnation, Ho said he would be willing to negotiate if the U.S. Operation ROLLING THUNDER bombing of the North ceased. Mai Van Bo, Hanoi's diplomatic representative in Paris, was named a point of contact. Since Hanoi would not communicate with an American official without a bombing halt, Kissinger served as an intermediary. Johnson made a speech, in San Antonio on September 29, offering the possibility of talks. They were rejected, although brought it up again in 1967. 
While the true strategic intent of the Tet Offensive of January 1968 is still debated, it clearly had an impact om American politics. In February, Walter Cronkite, then the most respected newsman in the U.S., announced he saw potential for nothing better than a stalemate. Other members of the press added to the call to retrench. Johnson announced a bombing halt on March 31, simultaneously announcing he would not run for re-election.
Nixon policy direction
Nixon directed the Joint Chiefs of Staff to prepare a six-step withdrawal plan. he Commandant of the Marine Corps General Leonard F. Chapman remembered, "I felt, and I think that most Marines felt, that the time had come to get out of Vietnam." Leading the ground force withdrawals, Marine redeployments started in mid-1969, and by the end of the year the entire 3d Marine Division had departed. 
While not all of the U.S. support, for reasons of domestic politics, was public, it included air attack on the North Vietnamese movements into the South, and combat service support including intelligence.
1969, for some South Vietnamese units, was a very good year. Palmer cites Sir Robert Thompson as the "year where there was accelerated pacification in the countryside. He points out that by mid-1971, all but three remote highways were safe to travel. Palmer agreed that by late 1969, the Viet Cong could be reduced to "but a nuisance." Doing so, however, did not remove the threat of PAVN units in sanctuaries within range of Saigon, continuing to present a threat of conventional invasion. Both the South and North Vietnamese planners looked at that threat; the decision was made to help the ARVN attack the sanctuaries in Cambodia.
For other South Vietnamese units, it was the beginning of a long slide into unsustainable situations.
After the Tet Offensive, ARVN units in areas where most of the enemy strength had been to NLF-VC, the ARVN were able to take an initiative. The Tet objectives were beyond our strength, concluded General Tran Van Tra, the commander of Vietcong forces in the South:
We suffered large sacrifices and losses with regard to manpower and materiel, especially cadres at the various echelons, which clearly weakened us. Afterwards, we were not only unable to retain the gains we had made but had to overcome a myriad of difficulties in 1969 and 1970.
Some ARVN units, especially that had been operating closely with U.S. troops or using facilities, could quickly move into a dominant role in their areas.
Others faced more of a challenge. For example, the ARVN 5th Division was directed to move from its existing base camp, Phu Cuong, to that of the U.S. 1st Infantry Division (U.S.) in Lai Khe while the U.S. division moved to southeast to Di An, nearer to Saigon. Both locations are districts in Binh Duong Province. This was not a simple replacement of the U.S. 1st ID by the ARVN 5th; the ARVN unit retained its previous operational responsibility. Also in the new area for the ARVN 5th had been the 1st Cavalry Divsion (Airmobile), far better equipped with helicopters than a standard U.S. division. In other words, one division was to take over the area covered by three, one of which had exceptional mobility.  At Phu Cong, MG Nguyen Van Hieu, the 5th Division commander, was able to use a local Popular Force battalion for base security. Popular Force battalions, however, did not move away from the area in which they were formed.
Joint operations against Cambodian sanctuaries
In 1969, Nixon ordered B-52 strikes against PAVN bases and supply routes in Cambodia. The orders for U.S. bombing of Cambodia were classified, and thus kept from the U.S. media and Congress. In a given strike, each B-52 normally dropped 42,000 pounds of bombs, and each strike consisted of of 3 or 6 bombers. Surviving personnel in the target area were apt to know they had been bombed, and, since the U.S. had the only aircraft capable of that volume, would know the U.S. had done it.
The "secrecy" may have been meant to be face-saving for Sihanouk, but there is substantial reason to believe that the secrecy, in U.S. military channels, was to keep knowledge of the bombing from the U.S. Congress and public. Actually, a reasonable case could be made that the bombing fell under the "hot pursuit" doctrine of international law, where if a neutral (Sihanouk) could not stop one country from attacking another from the neutral sanctuary, the attacked country(ies) had every right to counterattack.
Cambodian change of government
Much of North Vietnamese infiltration went through Cambodia. As well as unacknowledged bombing in Cambodia, Nixon authorized, while U.S. ground troops were still in South Vietnam, a large-scale ground attack into the Cambodian sanctuary. General Lon Nol had overhthrow Prince Norodom Sihanouk in March 1970; Sihanouk presented himself as a neutralist while aware of the PAVN use of his country.
Joint ground operations
Responding to a Communist attempt to take Cambodia, Nixon in April 1970 authorized a large scale US-ARVN incursion into Cambodia to directly hit the PAVN headquarters and supply dumps. The area bordered ARVN III Corps tactical zone  He preannounced the operation in a speech on April 30.
In this campaign, beginning May 1, U.S. Task Force Shoemaker, of the 1st Cavalry Division operated in the Fishhook area of Cambodia, preceded by B-52 strikes. TF Shoemaker operated with the ARVN Airborne Brigade. Separate ARVN operations took place in the Parrot's Beak area.
The incursion prevented the immediate takeover of Cambodia by Pol Pot and his Khmer Rouge, and cost the PAVN the supply line from the port of Sihanoukville. The Khmer Rouge broke with its North Vietnamese sponsors, and aligned with China. This made American involvement visible to the U.S. population, and there were intense protests, including deaths in a confrontation between rock-throwing protesters and poorly-trained National Guardsmen at Kent State University.
Intelligence and security
The first American soldier to die in Vietnam was a member of a communications intelligence unit. The U.S. intelligence collection systems, a significant amount of which (especially the techniques) were not shared with the ARVN, and, while not fully declassified, examples have been mentioned earlier in this article. The Communist side's intelligence operations, beyond the spies that were discovered, are much less known.
While there had been many assumptions that the South Vietnamese government was penetrated by many spies, and there indeed were many, a December 1969 capture of a Viet Cong communications intelligence center and documents revealed that they had been getting a huge amount of information using simple technology and smart people, as well as sloppy U.S. communications security.  This specific discovery was by U.S. Army infantry, with interpretation by regular communications officers; the matter infuriated GEN Abrams — at the communications specialists. Before and after, there had been a much more highly classified, and only now available in heavily censored form, National Security Agency analysis of how the Communists were getting their information, which has led to a good deal of modern counterintelligence and operations security. 
Some of the material from Touchdown also gave insight into the North Vietnamese intelligence system. For example, the NVA equivalent of the Defense Intelligence Agency was the Central Research Directorate (CRD) in Hanoi. COSVN intelligence staff, however, disseminated the tactically useful material.  Their espionage was under the control of the Military Intelligence Sections (MIS), which were directed by the Strategic Intelligence Section (SIS) of CRD.
U.S. direct discussions with North Vietnam
Subsequent congressional action banned further U.S. ground intervention outside the boundaries of South Vietnam, so the next major drive, Operation Lam Son 719, would have to be based on ARVN ground forces, U.S. air and artillery support, and U.S. advisory and logistical assistance.
The Vietnamization policy achieved limited rollback of Communist gains inside South Vietnam only, and was primarily aimed at providing the arms, training and funding for the South to fight and win its own war, if it had the courage and commitment to do so. By 1971 the Communists lost control of most, but not all, of the areas they had controlled in the South in 1967. The Communists still controlled many remote jungle and mountain districts, especially areas that protected the Ho Chi Minh Trail.
Commanded by Hoang Xuan Lam, known more for loyalty to Nguyen Van Thieu than for military talent, Saigon's effort to strike against one of these strongholds, Operation Lam Son 719, failed in 1971. The SVN forces, with some U.S. air support, were unable to defeat PAVN regulars. While the operation is detailed in a separate sub-article, the key issues were that the ARVN were inexperienced in executing large operations. They underestimated the needed forces, and the senior officers had developed in a context that rewarded loyalty rather than competence. Let there be no doubt that there were individual ARVN commanders that would be credit to any military, but, Thieu, like those RVN leaders before him, was constantly concerned at preventing a military coup. "...promotions were won in Saigon, not in battle. And vital to advancement was the avoidance of risk,even at the price of defeat."
Thieu relieved the operational commander, head of I Corps tactical zone commander Hoang Xuan Lam with the most respected combat commander in the ARVN, Do Cao Tri. Tri died 2.5 hours later in his first helicopter crash of inspection. It is known the crash was at low altitude; it has been argued it crashed due to mechanical failure or enemy fire. Certainly, mechanical failure was less demoralizing.
By the beginning of 1972, over 400,000 U.S. personnel had been withdrawn, virtually all combat troops. Politically, this let Nixon negotiate with China and the Soviet Union without the suggestion he was compromising U.S. soldiers in the field. 
North Vietnam made a major conventional attack on the South, for which the U.S. provided major air support under Operation LINEBACKER I, which enabled the ARVN to regain substantial control. When North Vietnam, late in the year, left the negotiating table, Nixon authorized the intensive Operation LINEBACKER II campaign, which forced the North Vietnamese to negotiate; a peace treaty was signed and all U.S. combat forces withdrew.
1973 and Ceasefire
The Armed Forces of the Republic of Vietnam had some excellent ground combat units, but still had very serious problems of command, control, and communications at division level and above.
Many units had become overdependent on American air support, and, while the RVN Air Force had not developed large-scale interdiction capability, they were also of varied quality for close air support. Beyond the issue that the Air Force was always fragmented to the corps commanders, they also did not receive various expected equipment upgrades. Photoreconnaissance was extremely limited.
Armored units had developed the greatest confidence in their ability to fight without U.S. air support. Ground commanders also learned that armored units were not for infantry support and static defenses, but needed to be used as mobile reserves. Neither North nor South Vietnam, however, ever really learned large-scale combined arms methods, compared to a NATO or Warsaw Pact level of proficiency.
- United States Department of Defense, Melvin R. Laird (January 22, 1969 - January 29, 1973), Secretaries of Defense
- Henry Kissinger (2003), Ending the Vietnam War: a History of America's involvement and extrication from the Vietnam War, Simon & Schuster, pp. 81-82
- Burr, William, ed. (November 2, 2007), Kissinger conspired with Soviet Ambassador to keep Secretary of State in the Dark, vol. George Washington University National Security Archive Electronic Briefing Book No. 233
- Palmer, Dave R. (1978), Summons of the Trumpet, Presidio Press, pp. 219-220
- Gibbs, James William (1986), The Perfect War: Technowar in Vietnam, Atlantic Monthly Press, p. 170
- Burr, William, ed. (November 2, 2007), Document 8: Their First “One-on-One”: Dobrynin’s record of meeting with Kissinger, 21 February 1969, pp. 20-25 of Soviet-American Relations: the Détente Years, 1969-1972, Kissinger conspired with Soviet Ambassador to keep Secretary of State in the Dark, vol. George Washington University National Security Archive Electronic Briefing Book No. 233
- Kissinger, pp. 41-42
- Lyndon Baines Johnson (March 31, 1968), President Lyndon B. Johnson's Address to the Nation Announcing Steps To Limit the War in Vietnam and Reporting His Decision Not To Seek Reelection
- Shumlimson, Jack, The Marine War: III MAF in Vietnam, 1965-1971, 1996 Vietnam Symposium: "After the Cold War: Reassessing Vietnam" 18-20 April 1996, Vietnam Center and Archive at Texas Tech University
- Tran Van Tra (2 February 1983), Vietnam: History of the Bulwark B2 Theater, vol. Volume 5, Concluding the 30 Years of War, Joint Publications Research Service, Foreign Broadcast Information Service, online by U.S. Army Combat Studies Institute
- Nguyen Van Tin (April 12, 2002), "Why Did Vietnamization of The Vietnam War Fail?", Fourth Triennial Symposium, Vietnam Center, Texas Tech University
- Smith, Russell H. (September-October 1971), "The Presidential Decision on the Cambodian Operation: A Case Study in Crisis Management", Air University Review
- Nixon, Richard M. (April 30, 1970), Address to the Nation on the Situation in Southeast Asia
- Tolson, John J. (1973), Chapter XI: The Changing War and Cambodia, 1969-1970, Vietnam Studies: Airmobility 1961-1971, Office of the Chief of Military History
- "The Death of a Fighting General", Time, March 8, 1971
- Fulghum, David & Terrence Mailand, South Vietnam on Trial - The Vietnam Experience., Boston Publishing Company
- Fiedler, David (Spring, 2003), "Project touchdown: how we paid the price for lack of communications security in Vietnam - A costly lesson", Army Communicator
- Center for Cryptologic History, National Security Agency (1993), PURPLE DRAGON: The Origin and Development of the United States OPSEC Program, vol. United States Cryptologic History, Series VI, The NSA Period, Volume 2
- Purple Dragon, p. 64
- Donaldson, Gary (1996), America at War Since 1945: Politics and Diplomacy in Korea, Vietnam, and the Gulf War, Greenwood Publishing Group, pp.120-124
- Karnow, Stanley (1983), Vietnam, a History, Viking Press, p. 630
- Karnow, p. 628
- "The Invasion Ends", Time, April 5, 1971
- Karnow, p. 636
- Smith, Homer D. (30 May 1975), End of Tour Report, pp. 3-4, 8-11
- Starry, Donn A., Chapter VIII: The Enemy Spring Offensive of 1972, Vietnam Studies: Mounted Combat in Vietnam, Office of the Chief of Military History, United States Army, pp. 218-219