The four years between the assassination of Ngo Dinh Diem in November 1963 and the Tet Offensive in January 1968 are the period of the principal American military escalation. The American troop commitment in South Vietnam rose from approximately 16,000 advisers in late 1963 to approximately 540,000 combat troops at peak in mid-1968 — a 30-fold expansion in five years and the largest American military mobilisation since the Korean War. The escalation was conducted under President Lyndon Johnson, who had inherited the Diem-era situation from Kennedy and who, across 1964-65, took the political decisions that converted an advisory-and-counterinsurgency commitment into a full conventional war. The political reasoning was the so-called domino theory — that the loss of South Vietnam to Communist forces would produce sequential Communist political gains across south-east Asia — combined with the Johnson administration's substantial fear that a perceived failure of American resolve would damage Johnson's domestic political position and his Great Society legislative agenda. The military reasoning was that conventional American firepower could compensate for the substantial political weakness of the post-Diem South Vietnamese government, which proved unable to consolidate a stable political authority through the post-coup period.
The post-coup chaos
The period between November 1963 and June 1965 was the most politically unstable in South Vietnamese history. Eight governments came and went in nineteen months: Big Minh (November 1963 – January 1964), Nguyen Khanh (January 1964 – February 1965), three further military caretaker governments, the brief premiership of Phan Huy Quat (February-June 1965), and the eventual stabilisation under the military junta of Nguyen Cao Ky and Nguyen Van Thieu in June 1965. The political instability substantially weakened the South Vietnamese state's capacity to conduct the counterinsurgency war; the NLF expanded its operational areas; the ARVN suffered an increasing number of tactical reverses (the Battle of Binh Gia in late December 1964 destroyed an ARVN regiment in three days; the Battle of Dong Xoai in June 1965 inflicted heavy casualties on a US-supported ARVN force). The American military advisers' assessments through this period concluded, increasingly, that the South Vietnamese state could not survive without substantial direct American combat involvement.
The Gulf of Tonkin
The Gulf of Tonkin incident of August 1964 provided the political pretext for the substantial expansion of American operational authority. On the 2nd of August the destroyer USS Maddox, conducting electronic-intelligence operations off the North Vietnamese coast in support of CIA-organised South Vietnamese commando raids on the coast, was attacked by three North Vietnamese torpedo boats. The Maddox returned fire and damaged the attacking craft without sustaining significant damage itself. On the 4th of August, the Maddox and a second destroyer, the USS Turner Joy, reported a second attack that — on the substantial documentary evidence later assembled, particularly the NSA Vietnam-period archives declassified in 2005 — almost certainly did not occur: the radar and sonar contacts that the destroyer commanders reported were probably false echoes generated by atmospheric conditions and the destroyers' own evasive manoeuvres. The Johnson administration, treating both incidents as confirmed attacks, requested and obtained from Congress on the 7th of August the Gulf of Tonkin Resolution authorising "all necessary measures to repel any armed attack against the forces of the United States and to prevent further aggression". The resolution passed the House 416-0 and the Senate 88-2 (the only opposing votes from Senators Wayne Morse and Ernest Gruening). It became the legal foundation of the substantial American military commitment that followed.
Rolling Thunder and the Marines
Operation Rolling Thunder — the sustained American strategic bombing campaign against North Vietnamese industrial, transport and infrastructure targets — opened on the 2nd of March 1965 and ran, with periodic pauses for negotiating overtures, until the 1st of November 1968. The campaign dropped approximately 864,000 tons of bombs on North Vietnamese territory across forty-four months — more than the American tonnage dropped in the entire Pacific theatre of the Second World War. The campaign's strategic effects were substantially less than its planners had hoped: the North Vietnamese economy was substantially less industrialised than European or Japanese economies, and its critical resources (Chinese-Soviet logistical support, rice agriculture, manpower replacement) were not vulnerable to strategic bombing in the way that the German or Japanese war economies had been. The North Vietnamese leadership, in retrospect, regarded the Rolling Thunder bombing as an annoyance rather than as an effective coercive measure; the population mobilisation that the bombing produced (the substantial volunteer labour mobilised to repair bomb damage, the political solidarity that the bombing reinforced) may, on the balance of subsequent scholarly assessment, have strengthened rather than weakened the North Vietnamese war effort.
The deployment of the Marines to Da Nang on the 8th of March 1965 — initially as airfield-protection forces — was the first commitment of American combat troops to South Vietnam. The escalation was rapid: 75,000 by July 1965, 184,000 by year-end, 385,000 by the end of 1966, 485,000 by the end of 1967, 540,000 by mid-1968. The American combat operations across 1965-67 — Operation Starlite (the first divisional-scale American operation, August 1965), the Ia Drang campaign (November 1965, the first major engagement between American forces and PAVN regulars), Operation Cedar Falls (the Iron Triangle clearance, January 1967), Operation Junction City (the largest American operation of the war, February-May 1967) — produced substantial tactical successes (inflicting heavy casualties on the NLF and PAVN forces involved) without producing strategic decisiveness (the insurgent forces could regenerate from the population and from northern reinforcement faster than American firepower could destroy them).
The pacification programme
The complementary pacification programme — the attempt to rebuild South Vietnamese political authority in the countryside through a combination of land reform, village-level government, civic action, and counter-NLF operations against political-network targets — was reorganised across 1966-67 as Civil Operations and Revolutionary Development Support (CORDS) under Robert Komer's direction. CORDS achieved substantial measurable improvements in the rural security indices across 1967-68, though the metrics were notoriously vulnerable to political-administrative manipulation and the substantive question of whether the pacification was producing durable political loyalty rather than merely surface compliance remained contested. The most controversial element of the pacification programme — the Phoenix Programme of selective targeting of NLF political cadres, conducted from 1967 onward under CIA direction — produced approximately 26,000 NLF deaths and 28,000 detentions across its operational lifetime (the figures are themselves contested), substantial collateral damage, and a lasting reputation problem for the American war effort.
The eve of Tet
By the end of 1967 the American Westmoreland command had publicly indicated that the war was being won — that the "crossover point" at which NLF and PAVN losses exceeded their replacement capacity was approaching. The substantive intelligence picture was less optimistic. The MACV's order-of-battle estimates were known internally to be politically constrained — a controversy that would surface in 1968 in the Sam Adams CIA dispute and again in 1982 in the CBS broadcast that became the subject of the Westmoreland v. CBS libel suit. The Tet Offensive of January 1968 would substantially confirm the more pessimistic internal assessments and would, more importantly, transform American public opinion of the war. Tet is the next chapter.
End of Chapter IV