Although North Vietnam’s Le Duc Tho signed the Paris Peace Accords in January 1973, he and his colleagues on the North Vietnamese Politburo remained committed to toppling the Saigon regime. Evidence of Hanoi’s intentions toward South Vietnam were not hard to discern – they were easily visible across the South Vietnamese landscape.
Immediately after the cease-fire went into effect, North Vietnam began a massive road-building program in the territories under its control in South Vietnam. The North also moved a huge amount of supplies into the South in preparation for future hostilities. Both of these actions were designed to give the Communists the capability of starting a major offensive on short notice, with the added bonus of being able to rapidly reinforce and resupply its forces engaged in combat.
The Communists initially focused their construction efforts on a road that the Americans called Corridor 613 or Ho Chi Minh Trail East. Corridor 613 ran entirely through former South Vietnamese territory that had fallen to the Communists prior to the Paris Accords. The route was not entirely new. Rather, much of it was pieced together from the South’s existing road network.
Corridor 613 began at the Demilitarized Zone (DMZ) north of Khe Sanh, passed by the old U.S. Marine base and then linked up with Route 9, which ran east to west from Dong Ha on the coast to the Laotian border. After briefly following Route 9 eastward, Corridor 613 turned south at today’s Dakrong Bridge. From there it cut a path through the mountains to the Ashau Valley. Once through the high-walled Ashau, Corridor 613 linked up with former French colonial Route 14, which connected Kham Duc, Dak Pek, and Dak To. Continuing south, the road skirted to the west of Kontum, Pleiku, and Ban Me Thuot, eventually terminating at Loc Ninh.
This new branch of the Ho Chi Minh Trail reduced travel times between North Vietnam and the far southern front lines in South Vietnam by several weeks.
By spring 1974, Corridor 613 possessed an extensive system of offshoots running to the east and southeast toward the populated South Vietnamese coastal plain. For instance, Route 547 tied the Communist logistical base in the Ashau Valley to the North Vietnamese combat troops of the 324B NVA Division stationed only a few miles southwest of Hue. Another side road ran down from the Central Highlands to the Que Son Valley, where the 711th NVA Division stood poised to strike at Danang, only twenty-five miles to the northwest. A third branch passed from Kham Duc through Quang Tin and Quang Ngai provinces. According to the CIA, “…this last route now extends more than 100 miles and is motorable into Binh Binh Province….” Binh Dinh had long been one of the central coast’s most populous and productive provinces; thus, both sides in the conflict desperately wanted control over the province’s abundant rice supplies and large peasant population. Additional branches of Corridor 613 entered War Zone C, the Iron Triangle, the area around Tay Ninh, and Binh Duong Province – the province immediately north of Saigon.
A little over a year after the signing of the Paris Accords, the North Vietnamese road system enabled Communist forces to move rapidly from North Vietnam to within thirty miles of Saigon. U.S. intelligence analysts stated that “…corridor  has about 500 miles of feeder roads extending out at strategic locations into the South Vietnamese countryside.” Those same officials remarked that “…Saigon’s advantage in mobility is gradually being offset by what officials call “Hanoi’s amazing road-building program.”
The CIA, Defense Department, and Nixon White House understood the military implications of the Communist’s road construction program. In a National Intelligence Estimate, CIA analysts reported, “The forward positioning of Communist forces and supplies and the improved road system give Hanoi the capability to kick off a major military campaign with little additional preparation, perhaps less than a month.”
That the Communists had the capability of launching a major military offensive against South Vietnam so soon after the Paris Accords went into effect attested to the feverish pace of their military activities across South Vietnam in 1973 and early 1974. It also indicated that the losses sustained by the North Vietnamese and Vietcong in personnel, supplies, weapons, and equipment during the 1972 Linebacker I and II air campaigns had been quickly replaced.
Although the Vietcong and North Vietnamese could have struck quickly and with great force against South Vietnam in 1974, they chose not to do so.
The CIA concluded in May 1974, “A major Communist offensive in South Vietnam is unlikely during 1974. The picture for the first half of 1975, however, is less clear…”
Why did the Communists forego a major offensive against the South in 1974? There are a number of possible explanations.
First, Hanoi recognized that the South Vietnamese still possessed impressive military capabilities. During operations Enhance and Enhance Plus, the Americans turned over to the South Vietnamese a tremendous amount of equipment, weaponry, and ammunition. In April 1974, the CIA observed that, “The South Vietnamese still hold an edge in firepower assets over the Communists on a countrywide basis.”
Second, Le Duc Tho and his colleagues on the Politburo preferred to take the South through political means rather than an outright military conquest. A political victory in the South would be more palatable to the North’s two major Communist allies – the Soviet Union and People’s Republic of China – both of which sought closer relations with the United States. On the other hand, a military defeat of the South would humiliate the United States and potentially sour U.S. relations with the two Communist giants.
Third, a major Communist offensive held the possibility of bringing the U.S. back into the war; while continued small-scale attacks and a protracted war strategy reduced the likelihood of American re-intervention. The North Vietnamese feared President Nixon. The president’s unpredictability, as expressed in the Madman Theory of leadership, and his violent response to the 1972 Easter Offensive, made the Communists cautious about carrying out another major offensive against the South while Nixon still occupied the White House. The last thing Hanoi wanted was the reappearance of American B-52s in the skies above North and South Vietnam.
Fourth, it is possible that the Communists did not strike a blow against South Vietnam in 1974 because they wanted to give the United States, and particularly Nixon, a decent interval before taking the South. In his military response to the Easter Offensive, Nixon had made it clear to the North Vietnamese that he wanted an interval between a U.S. military withdrawal from Vietnam and the collapse of the Saigon regime. The North Vietnamese appear to have learned their lesson during the Easter Offensive, when they lost an estimated 100,000 troops to U.S. firepower. Those losses, and the failure of the Easter Offensive in toppling the South Vietnamese government, may have persuaded Hanoi to give Nixon his interval.
But the most likely reason for delaying a major offensive in 1974 was that there was no imperative to launch such an offensive. The protracted war strategy was working. South Vietnam was being steadily weakened by political, economic, and military warfare. South Vietnam’s Nguyen Thieu faced increasing opposition from his Catholic base, peace activists, and Vietcong sympathizers. The South Vietnamese economy suffered from corruption, sky-high inflation, rising oil prices resulting from the Arab Oil Embargo, and Communist sabotage. Meanwhile, the North Vietnamese and Vietcong continued to nibble away at South Vietnamese territory and military strength through small-scale attacks. So the North Vietnamese did not need to go all-out for victory in 1974. They were steadily weakening the Saigon regime; and they recognized that if they simply bided their time, they might gain South Vietnam without a major, potentially bloody, offensive.
So 1974 passed without a big Communist military campaign. But that did not stop the North Vietnamese from continuing to prepare for a large-scale attack.
By December 1974, South Vietnam’s vulnerability to a major Communist offensive had increased substantially. During the preceding year, the Communists further strengthened their military position in the South by increasing their troop numbers, upgrading the quality and quantity of their weaponry, and by enhancing their mobility through a combination of road construction and the deployment of more tanks, armored personnel carriers, and trucks. In an end of the year report, the CIA concluded, “The Vietnamese Communists now have their strongest military force in South Vietnam in the history of the war.” However, the South Vietnamese military still packed a punch. The CIA noted in that same report, “There has been some decline in RVNAF [Republic of Vietnam Armed Forces] effectiveness in recent months, but this decline has not reached significant proportions.”
In late 1974, the CIA’s Vietnam experts at Langley did not believe the North Vietnamese would resort to a large-scale offensive in the near term. Nevertheless, they cautioned that if the opportunity to conquer South Vietnam with such an offensive presented itself, the Communists might be tempted to take it. The CIA concluded, “It is even possible, in response to a major opportunity, that the Communists would move to an all-out offensive…But our best judgment now is that they will not do so.”
Less the a month after the CIA dismissed the likelihood of a major offensive in the near term, the North struck against the South in what would become the final Communist offensive of the war.
On January 6, 1975, Communist forces took the province of Phuoc Long, located along the Cambodian border north of Saigon. The loss of this province, the first to be entirely lost to the Communists since the Paris Accords, demoralized the South Vietnamese. The former South Vietnamese Ambassador to the United States, Buu Vien, remarked that the South Vietnamese public became very dismayed after the defeat in Phuoc Long, “People began to lose confidence in what the government said and lost faith in the capability of the armed forces to protect the country.” This loss of confidence spread like a contagion through the ranks of the South Vietnamese military and government.
Emboldened by the ease with which they had taken Phuoc Long, and no longer worried about Nixon, who resigned the presidency in August 1974, the North Vietnamese decided the time had come to launch an all-out offensive against the South.
In the first week of March, Communist units isolated Ban Me Thout, a strategic town that anchored the South Vietnamese defense of the Central Highlands. On March 10, Ban Me Thout fell to Communist troops. Four days later, President Thieu ordered his forces out of the Central Highlands. The South Vietnamese withdrawal from the Central Highlands quickly turned into a rout. At Pleiku, panicked ARVN troops abandoned over 100,000 tons of ammunition, and millions of dollars worth of helicopters, artillery, tanks, armored personnel carriers, and planes to the advancing North Vietnamese. Of the estimated 60,000 South Vietnamese troops stationed across the Central Highlands, only about 20,000 made it down to the coastal plain, the rest either deserted, became POWs, or became casualties. In an obvious understatement, the CIA concluded that the “…redeployments [from the Highlands] have been generally disorderly.” An ARVN general offered a more frank assessment, “…[the pull-out from the Highlands] must rank as one of the worst planned and worst executed withdrawal operations in the annals of military history.”
Smelling blood, the Communists, aided by their previous prepositioning of troops and supplies, as well as their extensive road network, accelerated the timetable of their offensive. On March 14, they took Kontum and Pleiku without a fight, followed by Hue on March 25, and Danang on March 30.
Had they wanted to take Saigon in early April, the North Vietnamese could have done it. But the leaders in Hanoi decided to give the Americans and their South Vietnamese allies time to evacuate Saigon before they seized it.
On April 30, 1975, after waiting patiently for the last Americans to helicopter out of Saigon, the North Vietnamese and Vietcong rolled into the capital. The war was over.
The rapid success of the Communist offensive against South Vietnam was made possible in large part by the Communist road network that existed within South Vietnam. In a post-war analysis of the offensive, the commander of North Vietnamese forces in South Vietnam in 1975, General Van Tien Dung, admitted, “Our old and new communication lines (highways and pipelines) resembled endless lengths of sturdy hemp ropes being daily and hourly slipped around the neck and limbs of the monster who would be strangled with one sharp yank when the order was given.”
A former South Vietnamese general agreed with Dung, he said, “Communist strategy, very simple in nature, had not really changed in 1975, but the execution had been made easier and more effective, thanks to the new sophisticated net of roads.
South Vietnamese Lieutenant General Ngo Quang Truong, who commanded forces in Military Region 1, or what had been known as I Corps under the Americans, believed the Communists triumphed in 1975 because of their roads, which enabled North Vietnamese mechanized units to move so rapidly against cities such as Hue and Danang that South Vietnamese troops did not have enough time to organize an effective defense.
South Vietnam collapsed in a heap in the spring of 1975, not because of a lack of U.S. military aid or the neglect of the U.S. Congress, but because of war weariness amongst the South Vietnamese public, poor South Vietnamese military leadership, low ARVN troop morale, the disastrous decision by Thieu to withdraw from the Central Highlands, and, most importantly, the North Vietnamese Army’s road warriors, who, aided by an elaborate system of roadways, quickly overwhelmed South Vietnam’s defenses.
 Central Intelligence Agency, “South Vietnam: A Net Military Assessment,” Document: iim 74-003, April 2, 1974, page 3.
 New York Times, “U.S. Officials See a Vietnam Stalemate,” Leslie Gelb, May 7, 1974; New York Times, “Shaky Vietnam Accords,” David K. Shipler, January 17, 1975.
 Central Intelligence Agency, NIE 53/14.3.73, “Short-term Prospects for Vietnam,” October 12, 1973, page 2.
 Central Intelligence Agency, NIE 53/14.3 – 1 – 74, “The Likelihood of a Major North Vietnamese Offensive Against South Vietnam Before June 30, 1975,” May 23, 1974, page 1.
 Central Intelligence Agency, “South Vietnam: A Net Military Assessment,” Document: iim 74-003, April 2, 1974, page A-12.
 Central Intelligence Agency, NIE/14.3 – 2 – 74, “Short-term Prospects for Vietnam,” December 23, 1974, page ?
 Ibid., 6.
 Ibid., 2.
 Rand Corporation, “The Fall of South Vietnam: Statements by Vietnamese Military and Civilian Leaders,” (Santa Monica: Rand Corporation, December 1978), 81.
 Ibid., pages 94-96.
 Central Intelligence Agency, SNIE 53/14.3 – 75, “Assessment of the Situation in South Vietnam, 27 March 1975, page 2.
 Rand, “The Fall of South Vietnam,” page 96.
 Ibid., page 73.
 Ibid., page 79.
 Ibid., pages 111-114.