The Hồ Chí Minh trail (also known in Vietnam as the "Trường Sơn trail") was a logistical system that ran from the Democratic Republic of Vietnam (North Vietnam) to the Republic of Vietnam (South Vietnam) through the kingdoms of Laos and Cambodia. The system provided support, in the form of manpower and materiel, to the National Front for the Liberation of South Vietnam (called the Viet Cong or "VC" by its opponents) and the People's Army of Vietnam (PAVN), or North Vietnamese Army, during the Vietnam War.
It was named by the Americans after North Vietnamese president Hồ Chí Minh. Although the trail was mostly in Laos, the communists called it the Trường Sơn Strategic Supply Route (Đường Trường Sơn), after the Vietnamese name for the Annamite Range mountains in central Vietnam. According to the United States National Security Agency's official history of the war, the Trail system was "one of the great achievements of military engineering of the 20th century".
|Hồ Chí Minh Trail|
Ho Chi Minh Trail, 1967
|Controlled by||National Liberation Front|
|Battles/wars||Operation Barrel Roll
Operation Steel Tiger
Operation Tiger Hound
Operation Commando Hunt
Operation Lam Son 719
Ho Chi Minh Campaign
Operation Left Jab
Operation Honorable Dragon
Operation Diamond Arrow
Operation Thao La
Operation Black Lion
Phan Trọng Tuệ
Đồng Sỹ Nguyên
Hoàng Thế Thiện
Parts of what became the trail had existed for centuries as primitive footpaths that facilitated trade. The area through which the system meandered was among the most challenging in Southeast Asia: a sparsely-populated region of rugged mountains (500–2,400 metres (1,500–8,000 ft)), triple-canopy jungle and dense primeval rainforests. During the First Indochina War the Việt Minh maintained north/south communication using this system of trails and paths.
In 1959, Hanoi established the 559th Transportation Group under the command of Colonel (later General) Võ Bẩm to improve and maintain a transportation system to supply the NLF uprising against the South Vietnamese government. Originally, the North Vietnamese effort concentrated on infiltration across and immediately below the Demilitarized Zone that separated the two Vietnams.
As early as May 1958 PAVN and Pathet Lao forces had seized the transportation hub at Tchepone, on Laotian Route 9. This had been accomplished due to the results of elections in May that had brought a right-wing government to power in Laos, its increasing dependence on U.S. military and economic aid, and an increasingly antagonistic attitude toward North Vietnam. The 559th Group "flipped" its line of communications to the western side of the Trường Sơn mountains.
By 1959, the 559th had 6,000 personnel in two regiments alone, the 70th and 71st, not including combat troops in security roles or North Vietnamese and Laotian civilian laborers. In the early days of the conflict the trail was used strictly for the infiltration of manpower. This was due to the fact that Hanoi could supply its southern allies much more efficiently by sea.
After the initiation of U.S. naval interdiction efforts in coastal waters, known as Operation Market Time, the trail had to do double duty. Materiel sent from the north was stored in caches in the border regions that were soon retitled Base Areas, which, in turn, became sanctuaries for NLF and PAVN forces seeking respite and resupply after conducting operations within South Vietnam.
There were five large Base Areas (BAs) in the panhandle of Laos (see map). BA 604 was the main logistical center during the Vietnam War. From there, the coordination and distribution of men and supplies into South Vietnam's Military Region I and BAs further south was accomplished.
The notion of barefoot hordes pushing heavily-loaded bicycles, driving oxcarts, or acting as human pack animals, moving hundreds of tons of supplies in this manner was quickly supplanted by trucks (especially Soviet, Chinese, or Eastern Bloc models), which quickly became the main method of supply transportation. As early as December 1961, the 3rd Truck Transportation Group of PAVN's General Rear Services Department had become the first motor transport unit fielded by North Vietnamese to work the trail and the use of motor transport escalated.
Two types of units served under the 559th Group: "Binh Trams" and commo-liaison units. A "Binh Tram" was the equivalent of a regimental logistical headquarters and was responsible for securing a particular section of the network. While separate units were tasked with security, engineer, and signal functions, a "Binh Tram" provided the logistical necessities. Usually located one days march from one another, commo-liaison units were responsible for providing food, housing, medical care, and guides to the next way-station. By April 1965, command of the 559th Group devolved upon General Phan Trọng Tuệ, who assumed command of 24,000 men in six truck transportation battalions, two bicycle transportation battalions, a boat transportation battalion, eight engineer battalions, and 45 commo-liaison stations. The motto of the 559th became "Build roads to advance, fight the enemy to travel."
The system developed into an intricate maze of 5.5-metre-wide (18 ft) dirt roads (paved with gravel and corduroyed in some areas), foot and bicycle paths, and truck parks. There were numerous supply bunkers, storage areas, barracks, hospitals, and command and control facilities, all concealed from aerial observation by an intricate system of natural and man-made camouflage that was constantly expanded and replaced. By 1973, trucks could drive the entire length of the trail without emerging from the canopy except to ford streams or cross them on crude bridges built beneath the water's surface.
The weather in southeastern Laos came to play a large role both in the supply effort and in U.S./South Vietnamese efforts to interdict it. The southwest monsoon (commonly called the rainy season) from mid-May to mid-September, brought heavy precipitation (70% of 3,800 mm (150 in) per year). The sky was usually overcast with high temperatures. The northwest monsoon (the dry season), from mid-October to mid-March was relatively drier and with lower temperatures. Since the road network within the trail system was generally dirt, the bulk of supply transportation (and the military efforts that they supported) were conducted during the dry season. Eventually, the bulk of the trail was either asphalted or hard packed, thus allowing large quantities of supplies to be moved even during the rainy season.
In 1961 U.S. intelligence analysts estimated that 5,843 enemy infiltrators (actually 4,000) had moved south on the trail; in 1962, 12,675 (actually 5,300); in 1963, 7,693 (actually 4,700); and in 1964, 12,424. The supply capacity of the trail reached 20 to 30 tonnes per day in 1964 and it was estimated by the U.S. that 12,000 (actually 9,000) North Vietnamese regulars had reached South Vietnam that year. By 1965 the U.S. command in Saigon estimated that communist supply requirements for their southern forces amounted to 234 tons of all supplies per day and that 195 tons were moving through Laos.
U.S. Defense Intelligence Agency (DIA) analysts concluded that during the 1965 Laotian dry season the enemy was moving 30 trucks per day (90 tonnes) over the trail, far above the Saigon estimate, demonstrating a key problem which arose when discussing the North Vietnamese supply effort and U.S. attempts to halt it.
United States officials had only estimates of its enemy's capabilities; intelligence collection agencies often conflicted with each other. Thanks to improvements to the trail system (including opening new routes that would connect to the Sihanouk Trail in Cambodia), the amount of supplies transported during 1965 almost equaled the combined total for the previous five years. During the year interdiction of the system had become one of the top American priorities, but operations against it were complicated by the limited forces available at the time and Laos's ostensible neutrality.
The intricacies of Laotian affairs, and U.S. and North Vietnamese interference in them, led to a mutual policy of each ignoring the other, at least in the public eye. However, this didn't prevent the North Vietnamese from violating Laos's neutrality by protecting and expanding their supply conduit, and by supporting their Pathet Lao allies in their war against the central government. U.S. intervention came in the form of building and supporting a CIA-backed clandestine army in its fight with the Communists and constantly bombing the trail. They also provided heavy support for the Laotian government.
On 14 December 1964, the U.S. Air Force's "Operation Barrel Roll" carried out the first systematic bombardment of the Hồ Chí Minh trail in Laos. On 20 March 1965, after the initiation of Operation Rolling Thunder against North Vietnam, President Lyndon B. Johnson gave approval for a corresponding escalation against the trail system. "Barrel Roll" continued in northeastern Laos while the southern panhandle was bombed in "Operation Steel Tiger".
By mid-year the number of sorties being flown had grown from 20 to 1,000 per month. In January 1965, the U.S. command in Saigon requested control over bombing operations in the areas of Laos adjacent to South Vietnam's five northernmost provinces, claiming that the area was part of the "extended battlefield". The request was granted by the Joint Chiefs of Staff. The area fell under the auspices of "Operation Tiger Hound".
Political complications were not the only factors seriously hampering aerial operations. The seasonal monsoons that hindered communist supply operations in Laos also hampered the interdiction effort. These efforts were complicated by morning fog and overcast, and by the smoke and haze produced by the slash-and-burn agriculture practiced by the indigenous population. During 1968 the U.S. Air Force undertook two experimental operations that it hoped would exacerbate the worst parts of the above-mentioned weather patterns. "Project Popeye" was an attempt to indefinitely extend the rainy monsoon weather over southeastern Laos by cloud seeding. Testing on the project began in September above the Kong River watershed that ran through the Steel Tiger and Tiger Hound areas. Clouds were seeded by air with silver iodide smoke and then activated by launching a fuse fired from a flare pistol. 56 tests were conducted by October; 85% were judged to be successful. President Johnson then gave authorization for the program, which lasted until July 1972.
Testing on "Project Commando Lava" began on 17 May. Scientists from Dow Chemical had created a concoction that, when mixed with rainwater, destabilized the materials that made up soil and created mud. There was enthusiasm from the military and civilian participants in the program, who claimed they were there to "make mud, not war." In some areas it worked, depending on the makeup of the soil. The first mission was flown from Udorn Royal Thai Air Base by three C-130A aircraft from the 41st Tactical Airlift Squadron, Naha Air Base, Okinawa, Japan.
On the previous day, the three airmen from the squadron had scouted the target area south of Tchepone in a two engine CIA aircraft piloted by a civilian employee. The pilot had failed to load enough fuel on the reconnaissance aircraft and had to refuel at a Laotian base on the return trip to Udorn. Since United States armed forces personnel were never officially acknowledged as being in Laos, the United States Ambassador to Laos became enraged that U.S. personnel had been spotted in uniform at the remote refueling field in Laos.
The following day, the three aircraft departed from Udorn filled with tons of a mixture of nitrilotriacetic acid and sodium tripolyphosphate stuffed into cloth bags designed to break apart at impact. The aircraft flew above 5,000 feet (1,500 m) until near the target area, then let down to tree top level for the run-in to the target, flying an in-trail formation with 1,000 feet (300 m) between aircraft. Two A-1E Skyraider aircraft provided air cover to the mission. The target itself was a road cut sharply into a hillside on a long traverse.
The drop itself went as planned, with good coverage over the road for about 800 metres (1⁄2 mi). Later on in the day, the forecast rain activated the "soap" and the initial reports were that the entire road had washed into the valley. That night at a party at one of the local CIA watering holes, the C-130 crews and the CIA operatives celebrated the successful mission. Two other missions were flown by the same aircrews, operating out of Cam Ranh Air Base in South Vietnam. The targets on those two missions were at the northern end of A Shau Valley, in South Vietnam, but were unsuccessful.
The crews had been told that the North Vietnamese would rush hundreds of personnel to the drop site and remove the "soap" before the rainfall that was necessary to activate the chemicals. On the last mission, the third aircraft, commanded by Captain John Butterfield, was seriously damaged by ground fire. Although he managed to land at Chu Lai, the aircraft was a total loss due to a warped wing spar. For his actions on that day, Capt. Butterfield received the Silver Star medal. It was decided that the experiment didn't justify the risk, and the mission was officially cancelled.
On the ground, the CIA and the Royal Lao Army had initially been given the responsibility of stopping, slowing, or, at the very least, observing the enemy's infiltration effort. In Laos the agency began Operation Pincushion in 1962 for that reason. The operation evolved into Operation Hardnose, in which CIA-backed Laotian irregular reconnaissance team operations took place.
In October 1965, General Westmoreland received authorization to launch a U.S. military cross-border recon effort. On 18 November 1965, the first mission was launched "across the fence" and into Laos by the MACV-SOG. This was the beginning of an ever-expanding reconnaissance effort by MACV-SOG that would continue until the operation was disbanded in 1972. Another weapon in the American arsenal was unleashed upon the trail on 10 December 1965, when the first B-52 Stratofortress bomber strike was conducted in Laos.
A commonly occurring historical perspective concerning the interdiction effort tends to support the campaigns (regardless of their failure to halt or slow infiltration) due to the enemy material and manpower that it tied down in Laos and Cambodia. This viewpoint pervaded some official U.S. government histories of the conflict. John Schlight, in his A War Too Long, said of the PAVN's logistical apparatus:
"This sustained effort, requiring the full-time activities of tens of thousands of soldiers, who might otherwise have been fighting in South Vietnam, seems proof positive that the bombing of the Ho Chi Minh Trail had disrupted the North Vietnamese war effort."
The same historians would not consider the immense logistical effort fielded by the U.S. to sustain its military in Southeast Asia as a waste of manpower and resources, even if only one American soldier in four assigned to South Vietnam served in the combat arms.
Despite anti-infiltration efforts of the U.S. the estimated total of PAVN infiltrators for 1966 was between 58,000 and 90,000 men, including five full enemy regiments. A June 1966 DIA estimate credited the North Vietnamese with 1,000 km (600 mi) of truckable roads within the corridor, at least 300 km (200 mi) of which were good enough for year-round use. 1967 saw a change in command of the 559th Group as Senior Colonel (later General) Đồng Sỹ Nguyên assumed command. In comparison to the above DIA estimate, by the end of the year the North Vietnamese had completed 2,959 kilometers of vehicle capable roads, including 275 kilometers of main roads, 576 kilometers of bypasses, and 450 entry roads and storage areas.
It was learned by U.S. intelligence that the enemy was using the Kong and Bang Fai rivers to facilitate food, fuel, and munitions shipments by loading the materiel into half-filled steel drums and then launching them into the rivers. They were later collected downstream by systems of nets and booms. Unknown to the Americans the enemy had also begun to transport and store more than 81,000 tonnes of supplies "to be utilized in a future offensive". That future offensive was launched during the lunar new year Tết holiday of 1968, and to prepare for it, 200,000 PAVN troops, including seven infantry regiments and twenty independent battalions made the trip south.
Throughout the war, ground operations by conventional units were somewhat limited to brief incursions into border sanctuaries. One notable operation was Dewey Canyon which took place from 22 January to 18 March 1969 in I Corps. During the operation, the 9th Marine Regiment attempted to interdict NVA activity in the Da Krong River and A Shau Valleys. Ground units briefly entered the border areas of Laos during fighting with elements of the 9th NVA Regiment.
OPERATION TOLLROAD In November 1968 elements of the 4th Infantry Division, including Infantry and Combat Engineers, embarked from the Plei Trap Valley in Vietnam and proceeded to follow the Ho Chi Minh Trail into Cambodia and North into Laos, where they were extracted by helicopter on December 1. The mission was accomplished in two sections, the first in Cambodia, and the second when replacements were provided as the operation was crossing the Laotian border. The purpose of the mission was to render the trail unusable by creating abitis, destroying bunkers and bridges, and cratering the road. The incursion started on 25 November and ended December 1. The replacement units arrived on November 29. All personnel were removed by December 1. It is to be noted that on Thanksgiving evening a traditional Thanksgiving turkey dinner was delivered by helicopter to the troops in Laos per order of then-President Lyndon Johnson. The operation began at coordinates YA 747922 and the final extraction in Laos was at coordinates YB 726078. 
In the wake of the Tet Offensive, the North Vietnamese showed signs of expanding and modernizing their logistical effort. The number of supply and maintenance personnel had fallen, mainly due to increased use of motor/river transportation and mechanized construction equipment. The CIA estimated during the year that the 559th Group was using 20 bulldozers, 11 road graders, three rock crushers, and two steamrollers for maintenance and new road construction.
As many as 43,000 North Vietnamese or Laotians (most of whom were pressed into service) were engaged in operating, improving, or extending the system. In 1969, 433,000 tonnes of ordnance fell on Laos. This was made possible by the close-out of "Operation Rolling Thunder" and the commencement of "Operation Commando Hunt" in November 1968. U.S. aircraft were freed for interdiction missions and as many as 500 per day were flying over Laos. By the end of 1968, bombing missions over southern Laos had climbed 300 percent, from 4,700 sorties in October to 12,800 in November.
This round-the-clock aerial effort was directed by "Operation Igloo White", run out of Nakhon Phanom, Thailand. It was composed of three parts: strings of air-dropped acoustic and seismic sensors collected intelligence on the trail; computers at the Intelligence Collection Center (ICS) in Thailand collated the information and predicted convoy paths and speeds; and an airborne relay and control aircraft which received the signals from the sensors and routed aircraft to targets as directed by the ISC.
This effort was supported by MACV-SOG recon teams, who, besides carrying out recon, wiretap, and bomb damage assessment missions for "Commando Hunt", also hand-emplaced sensors for "Igloo White". Personnel interdiction was abandoned by early 1969. The sensor system was not sophisticated enough to detect enemy personnel, so the effort was given up until "Operation Island Tree" in late 1971. A revelation for U.S. intelligence analysts in late 1968 was the discovery of a petroleum pipeline running southwest from the northern port of Vinh.
Early in 1969, the pipeline crossed the Laotian frontier through the Mu Gia Pass and, by 1970, it reached the approaches to the A Shau Valley in South Vietnam. The plastic pipeline, assisted by numerous small pumping stations, managed to transfer diesel fuel, gasoline, and kerosene all through the same pipe. Due to the efforts of the PAVN 592nd Pipelaying Regiment, the number of pipelines entering Laos increased to six that year.
The 559th Group was made the equivalent of a Military Region in 1970 and again placed under the command of General Đồng Sỹ Nguyên. The unit was reorganized into five divisional headquarters: the 470th, 471st, 472nd, 473rd, and the 571st. The group consisted of four truck transportation regiments, two petroleum pipeline regiments, three anti-aircraft artillery (AAA) regiments, eight engineer regiments, and the 968th Infantry Division. By the end of 1970 the 559th was running 27 "Binh Trams", which transported 40,000 tonnes of supplies with a 3.4% loss rate during the year.
These supplies traveled in convoys from North Vietnam in relays, with trucks shuttling from only one way-station to the next. The vehicles were then unloaded and reloaded onto "fresh" trucks at each station. If a truck was disabled or destroyed, it was replaced from the assets of the next northern station and so on until it was replaced by a new one in North Vietnam. Eventually, the last commo-liaison station in Laos or Cambodia was reached and the vehicles were unloaded. The supplies were then cached, loaded onto watercraft, or man-portered into South Vietnam.
Due to the increased effectiveness of "Commando Hunt", North Vietnamese transportation units usually took to the roads only at dusk with the peak in traffic coming in the early hours of the morning. As American aircraft came on station, traffic would subside until just before dawn, when fixed-wing gunships and night bombers returned to their bases. The trucks then began rolling again, reaching another peak in traffic around 06:00 as drivers hurried to get into truck parks before sunrise and the arrival of the morning waves of U.S. fighter bombers. By the last phase of "Commando Hunt" (October 1970–April 1972), the average daily number of U.S. aircraft flying interdiction missions included 182 attack fighters, 13 fixed-wing gunships, and 21 B-52s.
The North Vietnamese also responded to the American aerial threat by the increased use of heavy concentrations of anti-aircraft artillery. By 1968 this was mainly composed of 37 mm and 57 mm radar-controlled weapons. The next year, 85 mm and 100 mm guns appeared, and by the end of Commando Hunt, over 1,500 guns defended the system.
Of all the weapons systems used against the trail, according to the official North Vietnamese history of the conflict, the AC-130 Spectre fixed-wing gunship was the most formidable adversary. The Spectres "established control over and successfully suppressed, to a certain extent at least, our nighttime supply operations". The history claimed that allied aircraft destroyed some 4,000 trucks during the 1970–1971 dry season, of which the C-130s alone destroyed 2,432 trucks.
A countermeasure to the Spectre came on 29 March 1972, when a Spectre was shot down on a night mission by a surface-to-air SA-7 missile near Tchepone. This was the first U.S. aircraft shot down by a SAM that far south during the conflict. PAVN responded to U.S. nighttime bombing by building the 1,000 kilometer-long Road K ("Green Road") from north of Lum Bum to lower Laos. During "Commando Hunt IV" (30 April through 9 October 1971), U.S., South Vietnamese, and Laotian forces began to feel the North Vietnamese reaction to General Lon Nol's coup in Cambodia and the subsequent closure of the port of Sihanoukville to its supply shipments. As early as 1969 PAVN had begun its largest logistical effort of the entire conflict.
The Laotian towns of Attapeu and Saravane, at the foot of the Bolaven Plateau were seized by the North Vietnamese during 1970, opening the length of the Kong River system into Cambodia. Hanoi also created the 470th Transportation Group to manage the flow of men and supplies to the new battlefields in Cambodia. This new "Liberation Route" turned west from the trail at Muong May, at the southern end of Laos, and paralleled the Kong River into Cambodia. Eventually this new route extended past Siem Prang and reached the Mekong River near Stung Treng.
During 1971 PAVN took Paksong and advanced to Pakse, at the heart of the Bolaven Plateau region of Laos. The following year, Khong Sedone fell to the North Vietnamese. PAVN continued a campaign to clear the eastern flank of the trail that it had begun in 1968. By 1968, U.S. Special Forces camps at Khe Sanh and Khâm Đức, both of which were used by MACV-SOG as forward operations bases for its reconnaissance effort, had either been abandoned or overrun. In 1970, the same fate befell another camp at Dak Seang. What had once been a 30-kilometre-wide (20 mi) supply corridor now stretched for 140 km (90 mi) from east to west.
In early February 1971, 16,000 (later 20,000) ARVN troops rolled across the Laotian border along Route 9 and headed for the PAVN logistical center at Tchepone. "Operation Lam Son 719", the long-sought assault on the Ho Chi Minh trail itself and the ultimate test of the American policy of Vietnamization, had begun. Unfortunately for the South Vietnamese, U.S. ground troops were prohibited by law from participation in the incursion, and the U.S was restricted to providing air support, artillery fire and helicopter aviation units.
At first the operation went well, with little resistance from the North Vietnamese. By early March 1971 the situation was changing. Hanoi made the decision to stand and fight. It began to muster forces which would eventually number 60,000 PAVN troops as well as several thousand allied Pathet Lao troops and Lao irregulars, outnumbering the ARVN by almost three to one.
The fighting in southeastern Laos was unlike any yet seen in the Vietnam War, since the PAVN abandoned its old hit-and-run tactics and launched a conventional counterattack. The PAVN first launched massed infantry attacks supported by armor and heavy artillery to crush ARVN positions on the flanks of the main advance. Coordinated anti-aircraft fire made tactical air support and resupply difficult and costly, with 108 helicopters shot down and 618 others damaged.
PAVN forces began to squeeze in on the main line of the advance. Although a heliborne assault managed to seize Tchepone, it was a useless victory, since the South Vietnamese could only hold the town for a short period of time before being withdrawn due to attacks on the main column. The only way the invasion force managed to extricate itself from Laos was through the massive application of American airpower. By 25 March 1971 the last ARVN troops recrossed the border, closely followed by their enemy. As a test of Vietnamization, "Lam Son 719" failed; one-half of the invasion force was lost during the operation.
South Vietnamese troops were poorly led and the elite Ranger and Airborne elements had been decimated. "Lam Son 719" did manage to postpone a planned PAVN offensive against the northern provinces of South Vietnam for one year. By spring 1972 the Americans and South Vietnamese realized that the enemy was planning a major offensive, but they did not know where or when. The answer came on 30 March 1972 when 30,000 PAVN troops, supported by more than 300 tanks crossed the border and invaded Quảng Trị Province. The "Nguyen Hue Offensive" (better known as the "Easter Offensive") was underway.
As South Vietnamese forces were on the verge of collapse, President Richard M. Nixon responded by increasing the magnitude of the American aerial assault (due to the withdrawal of U.S. aviation units from Southeast Asia, squadrons were flown into South Vietnam from Japan and the U.S. itself). The effort failed to halt the fall of Quảng Trị City on 2 May, seemingly sealing the fate of the four northernmost provinces. Due to the adoption of a conventional offensive (and the logistical effort needed to support it), PAVN placed itself squarely in the sights of U.S. air power and the casualties were high.
The situation was complicated for the Americans by the launching of two smaller attacks by the North Vietnamese: the first aimed to seize Kon Tum in the Central Highlands, and threatened to cut South Vietnam in two; the second prompted a series of savage battles in and around An Lộc, the capital of Bình Long Province. A total of 14 PAVN divisions were now committed to the offensive. On 13 May 1972, South Vietnam launched a counteroffensive with four divisions backed by massive U.S. air support. By 17 May, Quảng Trị City was retaken, but the South Vietnamese military ran out of steam. The PAVN thrusts against Kon Tum and An Lộc were contained. During these operations, the North Vietnamese suffered approximately 100,000 casualties while the South Vietnamese suffered 30,000 fatalities during the fighting.
The seizure of territory within South Vietnam itself allowed Hanoi to extend the trail across the border with Laos and into that country. The signing of the Paris Peace Accords seemed to bring the conflict in Southeast Asia to an end. The last U.S. forces departed in March 1973. Both North and South Vietnamese were to maintain control in the areas under their influence and negotiations between the two nations, possibly leading to a coalition government and unification, were to take place. Jockying for control of more territory, both sides flagrantly violated the cease-fire and open hostilities began anew.
By 1973, the PAVN logistical system consisted of a two-lane paved (with crushed limestone and gravel) highway that ran from the mountain passes of North Vietnam to the Chu Pong Massif in South Vietnam. By 1974 it was possible to travel a completely paved four-lane route from the Central Highlands to Tây Ninh Province, northwest of Saigon. The single oil pipeline that had once terminated near the A Shau Valley now consisted of four lines (the largest eight inches in diameter) and extended south to Lộc Ninh. In July 1973 the 259th Group as redesignated the Truong Son Command, the regimental sectors were converted to divisions, and the binh trams were designated as regiments. By late 1974 forces under the new command included AAA Division 377, Transportation Division 571, Engineering Division 473, the 968th Infantry Division, and sectoral divisions 470, 471, and 472.
Command then devolved upon Major General Hoàng Thế Thiện. In December 1974 the first phase of a limited PAVN offensive in South Vietnam began. Its success inspired Hanoi to try for an expanded but still limited, offensive to improve its bargaining position with Saigon. In March, General Văn Tiến Dũng launched "Campaign 275", the success of which prompted the general to push Hanoi for a final all-out offensive to take all of South Vietnam. After an ineffective attempt to halt the offensive, Saigon fell to North Vietnamese forces on 30 April 1975.