As the Americans withdrew, South Vietnam's combat capability declined. The United States furnished its allies the heavier M48 tank to match the NVA's T54 tank and heavier artillery to counter North Vietnamese 130mm guns, though past experience suggested that additional arms and equipment could not compensate for poor skills and mediocre leadership.
In fact, the weapons and equipment were insufficient to offset the reduction in U.S. combat strength. In mid-1969, for example, an aggregate of fifty-six allied combat battalions were present in South Vietnam's two northern provinces; in 1972, after the departure of most American units, only thirty battalions were in the same area. Artillery strength in the northern region declined from approximately 400 guns to 169 in the same period, and ammunition supply rates fell off as well.
Similar reductions took place throughout South Vietnam, causing decreases in mobility, firepower, intelligence support, and air support. Five thousand American helicopters were replaced by about 500. American specialties -- B-52 strikes, photo reconnaissance, and the use of sensors and other means of target acquisition -- were drastically curtailed.
Such losses were all the more serious because operations in Cambodia and Laos had illustrated how deeply ingrained in the South Vietnamese Army the American style of warfare had become. Nearly two decades of U.S. military involvement were exacting an unexpected price. As one ARVN division commander commented, "Trained as they were through combined action with US units, the [South Vietnamese] unit commander was used to the employment of massive firepower." That habit, he added, "was hard to relinquish."
By November 1971, when the 101st Airborne Division withdrew from the South, Hanoi was planning its 1972 spring offensive. With ARVN's combat capacity diminished and nearly all U.S. combat troops gone, North Vietnam sensed an opportunity to demonstrate the failure of Vietnamization, hasten ARVN's collapse, and revive the stalled peace talks. In its broad outlines and goals, the 1972 offensive resembled Tet 1968, except that the North Vietnamese Army, instead of the Viet Cong, bore the major burden of combat. The Nguyen-Hue offensive or Easter offensive began on 30 March 1972. Total U.S. military strength in South Vietnam was about 95,000, of which only 6,000 were combat troops, and the task of countering the offensive on the ground fell almost exclusively to the South Vietnamese.
Attacking on three fronts, the North Vietnamese Army poured across the demilitarized zone and out of Laos to capture Quang Tri, South Vietnam's northernmost province. In the Central Highlands, enemy units moved into Kontum Province, forcing Saigon to relinquish several border posts before government forces contained the offensive.
On 2 April, Viet Cong and North Vietnamese forces struck Loc Ninh, just south of the Cambodian border on Highway 13, and advanced south to An Loc along one of the main invasion routes toward Saigon.
A two-month-long battle ensued, until enemy units were driven from An Loc and forced to disperse to bases in Cambodia. By late summer the Easter offensive had run its course; the South Vietnamese, in a slow, cautious counteroffensive, recaptured Quang Tri City and most of the lost province. But the margin of victory or defeat often was supplied by the massive supporting firepower provided by U.S. air and naval forces.
The tactics of the war were changing. Communist forces now made extensive use of armor and artillery. Among the new weapons in the enemy's arsenal was the Soviet SA-7 hand-held antiaircraft missile, which posed a threat to slow-flying tactical aircraft and helicopters. On the other hand, the Army's atfack helicopter, the Cobra, outfitted with TOW antitank missiles, proved effective against NVA armor at stand-off range. In their anti-tank role, Army attack helicopters were crucial to ARVN's success at An Loc, suggesting a larger role for helicopters in the future as part of a combined arms team in conventional combat.
Vietnamization continued to show mixed results. The benefits of the South Vietnamese Army's newly acquired mobility and firepower were dissipated as it became responsible for securing areas vacated by American forces. Improvements of territorial and paramilitary troops were offset as they became increasingly vulnerable to attack by superior North Vietnamese forces. Insurgency was also reviving. Though their progress was less spectacular than the blitzkrieg-like invasion of the South, North Vietnamese forces entered the Delta in thousands between 1969 and 1973 to replace the Viet Cong--one estimate suggested a tenfold increase in NVA strength, from 3000 to 30,000, in this period. Here the fighting resembled that of the early 1960's, as enemy forces attacked lightly defended outposts and hamlets to regain control over the rural population in anticipation of a cease-fire. The strength of the People's Self-Defense Force, Saigon's first line of hamlet and village defense, after steady increases in 1969 and 1970, began to decline after 1971, also suggesting a revival of the insurgency in the countryside. Pursuing a strategy used successfully in the past, the North Vietnamese forced ARVN troops to the borders, exposing the countryside and leaving its protection in the hands of weaker forces.
Such unfavorable signs, however, did not disturb South Vietnam's leaders as long as they could count on continued United States air and naval support. Nixon's resumption of the bombing of North Vietnam during the Easter offensive and, for the first time, his mining of North Vietnamese ports encouraged this expectation, as did the intense American bombing of Hanoi and Haiphong in late 1972. But such pressure was intended, at least in part, to force North Vietnam to sign an armistice.
If Thieu was encouraged by the display of U.S. military muscle, the course of negotiations could only have been a source of discouragement. Hanoi dropped an earlier demand for Thieu's removal, but the United States gave up its insistence on Hanoi's withdrawal of its troops from the South. In early 1973 the United States, North and South Vietnam, and the Viet Cong signed an armistice that promised a cease-fire and national reconciliation. In fact, fighting continued, but the Military Assistance Command was dissolved, remaining U.S. forces withdrawn, and American military action in South Vietnam terminated. Perhaps most important of all, American advisers -- still in many respects the backbone of ARVN's command structure -- were withdrawn.
Decline
Between 1973 and 1975 South Vietnam's military security further declined through a combination of old and new factors. Plagued by poor maintenance and shortages of spare parts, much of the equipment provided Saigon's forces under Vietnamization became inoperable. A rise in fuel prices stemming from a worldwide oil crisis further restricted ARVN's use of vehicles and aircraft. South Vietnamese forces in many areas of the country were on the defensive, confined to protecting key towns and installations.
Seeking to preserve its diminishing assets, the South Vietnamese Army became garrison bound and either reluctant or unable to react to a growing number of guerrilla attacks that eroded rural security. Congressionally mandated reductions in U.S. aid further reduced the delivery of repair parts, fuel, and ammunition. American military activities in Cambodia and Laos, which had continued after the cease-fire in South Vietnam went into effect, ended in 1973 when Congress cut off funds. Complaining of this austerity, President Thieu noted that he had to fight a "poor man's war."
Vietnamization's legacy was that South Vietnam had to do more with less.
In 1975 North Vietnam's leaders began planning for a new offensive, still uncertain whether the United States would resume bombing or once again intervene in the South. When their forces overran Phuoc Long Province, north of Saigon, without any American military reaction, they decided to proceed with a major offensive in the Central Highlands. Neither President Nixon, weakened by the Watergate scandal and forced to resign, nor his successor, Gerald Ford, was prepared to challenge Congress by resuming U.S. military activity in Southeast Asia. The will of Congress seemed to reflect the mood of an American public weary of the long and inconclusive war.
What had started as a limited offensive in the highlands to draw off forces from populated areas now became an all-out effort to conquer South Vietnam. Thieu, desiring to husband his military assets, decided to retreat rather than to reinforce the highlands. The result was panic among his troops and a mass exodus toward the coast. As Hanoi's forces spilled out of the highlands, they cut off South Vietnamese defenders in the northern provinces from the rest of the country. Other NVA units now crossed the demilitarized zone, quickly overrunning Hue and Da Nang, and signaling the collapse of South Vietnamese resistance in the north. Hurriedly established defense lines around Saigon could not hold back the inexorable enemy offensive against the capital. As South Vietnamese leaders waited in vain for American assistance, Saigon fell to the Communists on 29 April 1975.
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