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No factor loomed as large in the war as keeping North Vietnam’s men and materiel from rolling down the Ho Chi Minh Trail.

The Vietnam War was contested in ten thousand places, from the U Minh Forest in the Mekong Delta to the Ia Drang Valley in the Central Highlands, from Tay Ninh Province near the Cambodian border to the rugged mountains framing Khe Sanh on the Laotian frontier. And for the millions of combatants—whatever their allegiance—every battle played out differently, each experience proved to be unique. Except for the ubiquitous fighting and dying, the 1964 guerrilla clashes in the rice paddies of the Delta bore little resemblance to a 1969 head-to-head slugfest in the A Shau Valley known as “Hamburger Hill.” Disparate as their experiences were, one constant emerged: Every soldier, every guerrilla, every general was personally affected by the Ho Chi Minh Trail.

Originally nothing more than a series of primitive footpaths meandering through the primordial rain forests of the southern panhandle of Laos, what was to become the Ho Chi Minh Trail initially served as a crude conduit for moving Viet Minh troops and supplies against French forces during the early 1950s. But in 1959, North Vietnam’s ruling Lao Dong Party adopted Resolution 15, calling for support of the Viet Cong movement in South Vietnam. With that watershed decision, Colonel Vo Bam of the People’s Army of Vietnam (PAVN) was assigned the task of “organizing a special communication line to send supplies to the revolution in the South.” From that moment on, the crux of the entire Vietnam War hinged on Hanoi’s efforts to sustain the vital logistics supply line down the trail, and American attempts to interdict and cut it.

In the beginning, Colonel Vo Bam could only manage a few tons of supplies carried down the trail on bicycles, pack animals or on the backs of porters. Within a decade, however, a honeycomb network of 12,000 miles of roads, rivers and highspeed trails was operating through Laos, beginning at Mu Gia Pass in the North and crossing into South Vietnam at the A Shau Valley or into the Central Highlands provinces of Pleiku and Kontum. An extension through northern Cambodia also channeled troops and supplies into Tay Ninh Province northwest of Saigon.

There were major sections of the trail that U.S. forces never knew about. Where naturally thick vegetation didn’t conceal it from above, North Vietnamese engineers and support forces constructed elaborate bamboo trellises along the road network to hide all traces of the trail. While late in the war the PAVN even moved tanks undetected all the way south, the primary U.S. interdiction effort focused on trucks. Conservative intelligence estimates put the North Vietnamese truck inventory in Laos at 2,500 to 3,000 during the 1970-71 dry seasons, with from 500 to 1,000 moving per night—each capable of carrying about four tons of supplies.

The North Vietnamese crusade to overthrow the Saigon government depended on the Ho Chi Minh Trail. The process by which supplies and men moved south was labor-intensive and extremely complex, requiring numerous transfers of cargo in and out of vehicles to camouflaged storage caches along the network. Colonel Vo Bam’s 559th Transportation Group conducted virtually all movement at night in a series of brief shuttles from one way station to the next, rather than by long-distance hauling. Truck drivers took their vehicles over the same routes night after night, becoming thoroughly familiar with their segments. Periods of full moon light, which allowed travel without headlights,and low cloud cover were exploited to avoid detection from overhead aircraft. Truck movement typically began shortly after dusk. Traffic normally began trailing off between 3 and 6 a.m., to allow time for unloading and concealing supplies and vehicles before the arrival of the first wave of fighter-bombers. The system may have been cumbersome and inefficient, but it worked.

When a few North Vietnamese units along the trail endeavored to speed up the pace in 1968-69 by running small convoys during daylight, they got a rude shock when forward air controllers (FACs) flying in the newly introduced OV-10 Bronco pressed the attack. One defector, whose unit tried a dash in broad daylight, confessed that his comrades were stunned by the accuracy of this new FAC aircraft.“After this strike,”he said, “we were afraid of the OV-10s,” a fear that convinced them to return to the tried-and-true nighttime regimen.

By late in the war, the Ho Chi Minh Trail was a far cry from the primitive hodgepodge of jungle paths of a decade earlier. Troops and supplies moving south used 18-foot-wide camouflaged highways “dotted with truck rest and service areas, oil tanks, machine shops, and other installations, all protected by hilltop antiaircraft emplacements,” wrote Vietnam historian Stanley Karnow.

As a way to leverage vast U.S. technological superiority, the notion of an electronic battlefield first took root early in January 1966, when Harvard Law School professor Roger Fisher suggested the idea of an “infiltration barrier” to stop the flow of men and equipment into South Vietnam. That summer, four distinguished scientists from Harvard and MIT approached the Department of Defense about arranging a “summer study” of technical alternatives in Vietnam. Referred to as the Jason Group, it concluded that the bombing campaign against the North was having no real effect on the fighting in the South.

Beginning in March 1965, the principal American interdiction effort had focused on Operation Rolling Thunder, an aerial bombardment campaign against targets in North Vietnam intended to force Hanoi to end the war. Secretary of Defense Robert McNamara came to the conclusion that the United States could not “bomb the North sufficiently to make a radical impact on Hanoi’s political, economic and social structure.” He went on to correctly predict that continued bombing“would not be stomached either by our own people or by world opinion.” There had to be another way.

Instead of bombing North Vietnam, the Jason Group scientists recommended the creation of an “air-supported barrier” concentrating on choke points outside the North. McNamara agreed and authorized the development of weapons and techniques needed for systematically attacking infiltration traffic on the Ho Chi Minh Trail. On Nov. 11, 1968, the Seventh Air Force in Saigon initiated the new campaigns, code-named “Commando Hunt.”These campaigns each lasted roughly six months, corresponding to the wet and dry seasons in Laos. In all, U.S. aerial interdiction forces engaged in seven Commando Hunt campaigns from 1968 to 1972.

In late 1970, FAC pilots were noticing unusually heavy truck traffic moving south along the trail. The “night fighter” Cessna O-2 jocks witnessed the traffic on almost every mission, but they also received invaluable data from 20,000 electronic“snoopers.” A sophisticated network of battery-powered acoustic and seismic sensors, code-named“Igloo White,”dotted the entire length of the trail, monitoring enemy traffic. The network consisted of three parts: sensors, orbiting aircraft to relay the signals and the 200,000-square-foot Infiltration Surveillance Center at Nakhon Phanom Air Base in Thailand, operated by Task Force Alpha.

Fast-moving jets such as F-4 Phantoms usually dropped the sensors during high-speed, low-altitude dashes—500 feet above the ground at 550 knots—along selected trail segments. On occasion, helicopters, Studies and Observation Group (SOG) reconnaissance teams or even Marine OV-10s planted various types of sensors. There were also chemical sniffers, engine-ignition detection devices and simple radio relays that could actually hear each truck pass a given point along the trail. Specially equipped orbiting aircraft, such as the EC-121 “Batcat” and the QU-22B“Pave Eagle,”picked up the signals and relayed them to Task Force Alpha at Nakhon Phanom. There, intelligence analysts studied the raw data, aided by the most powerful computer at the time, IBM’s 360/65. Using visual and electronic tools, task force members plotted numbers, times and locations as enemy trucks motored south each night.As one analyst noted, “We wired the Ho Chi Minh Trail like a drugstore pinball machine and we plugged it in every night.” Predictably, the lights, bells and whistles on their consoles earned them the somewhat disparaging nickname of “pinball wizards.” Task Force Alpha could track individual trucks as they passed consecutive sensors, but more important the analysts could tell when the traffic pulled off the road before reaching the next sensor. The interruption generally meant one thing: a truck park. And that’s when the FACs went to work, calling in airstrikes against suspected truck staging areas or transshipment points.

The entire Igloo White network, part of the so-called McNamara Line, was a high-tech solution to the problem of disrupting Hanoi’s vital logistics and supply line. Hanoi responded with a variety of inventive low-tech countermeasures. To fool the seismic sensors, NVA road crews drove herds of animals up and down the paths and roads. To limit the effectiveness of the chemical sensors, they hung buckets of urine from tree branches. And when they could find sound sensors, road crews simply moved them to some useless location. The battle of the trail literally became what historian John Prados called a contest between “technology and ingenuity.”

Though Igloo White gave the Americans a remarkable advantage on the electronic battlefield, it still had its limitations. As Air Force Maj. Gen.William J. Evans, responsible for the electronic battlefield in Southeast Asia, explained in 1971: “We are not bombing a precise point on the ground—we can’t determine each truck’s location that accurately with ground sensors, which are listening—not viewing—devices. Since we never actually‘see’ the trucks as point targets, we use area-type ordnance to cover the zone we know the trucks to be in.”

Those“listening devices”—acoubuoy acoustic sensors—used in Igloo White managed to provide a few lighter moments for a Senate committee reviewing the tapes. In one instance, a North Vietnamese NCO was heard telling a trooper to climb a tree to get a parachute from a three-foot-long acoubuoy caught in the top branches. It seems he wanted to give the material to his girlfriend to make a dress. In another instance, the sound of axes could be heard as a bungling work crew chopped down a tree to obtain a sensor caught in its foliage. That was followed by the sound of a crash and screaming as the tree apparently fell on them.

How successful were Igloo White and the Commando Hunt campaigns against the trail? To this day researchers and historians still debate, often heatedly, about claims versus results and execution at odds with policy. From the beginning, historians have emphasized that the piecemeal, confusing interdiction policy percolated at the very heart of the debate, adding to bureaucratic discord. Even former Secretary of Defense McNamara conceded as much. In subscribing to the military strategy of thwarting Hanoi’s supply efforts through aerial interdiction, McNamara confessed that he and the Joint Chiefs of Staff never fully assessed “the probability of achieving the objectives, how long it might take or what it would cost in lives lost, resources expended, and risks incurred.”In other words, there was never any plan or mechanism in place to measure success. Consequently, Seventh Air Force planners devised one yardstick while the CIA came up with another. Controversy was bound to ensue.

In part, the argument simmered because the stated objectives of Commando Hunt were actually more limited than the currently held construct. While many historians accept as a matter of faith that the mission was to shut down the Ho Chi Minh Trail, the goal of the Commando Hunt campaigns was not to halt infiltration, but rather to make the North Vietnamese pay too heavy a price for their effort.

True, American planners hoped to destroy as many trucks as possible, to tie down enemy manpower and to test the effectiveness of the sensor system, but total strangulation from the air was never deemed feasible. For example, during the 1970-71 dry season, the Seventh Air Force estimated that Hanoi pumped some 60,000 tons of supplies down the trail, at least 10,000 tons of which actually made it to NVA troops in South Vietnam. According to William W. Momyer, former Seventh Air Force commander, that 16 percent arrival rate represented an acceptable return on investment for Commando Hunt.

Statistics were the name of the game during Commando Hunt. Since the Seventh Air Force had no easily definable criteria by which to measure success or failure, and since the chain of command demanded at least some gauge of achievement, “truck count”entered the lexicon to quantify events on the trail, as“body count”had for land battles. But confirming a truck kill wasn’t easy. Although only a few trucks were destroyed during daylight hours, FACs and photoreconnaissance could visually authenticate those destroyed vehicles. At night, however, most of the strikes were against unseen targets moving through jungle cover. Even when there were fires or explosions, it was difficult to determine the damage inflicted. Still, some Seventh Air Force generals believed the truck kill figures implicitly.

Historian Earl Tilford has offered a personal account of such an incident. While delivering the morning intelligence briefing at Seventh Air Force headquarters in Saigon, he recalled, “After I had briefed that over 300 trucks had been destroyed or damaged the previous night, the general leaned back in his chair and stated, ‘Gentlemen, what we have here is the end of North Vietnam as a viable fighting power.’” The next night the trail was as busy as ever. Reflecting on that briefing, Tilford came to the conclusion that“for all the perceived successes in that numbers game, the Air Force succeeded only in fooling itself into believing Commando Hunt was working.”

With pressure mounting to produce results, the truck kill numbers grew dramatically, soaring in 1970 to a high of 12,368. The CIA vigorously contested that figure, reporting that Air Force claims exceeded by 6,000 the total number of trucks believed to exist in all of North Vietnam! To the CIA, this was yet another demonstration of the foibles of military thinking. The Air Force’s credibility suffered even more when it published the final tally for all seven Commando Hunt campaigns: 46,000 trucks destroyed or damaged.

No doubt some inflation and error was present in the Air Force estimates, but as air power expert John Correll noted, if Air Force claims could be disputed, so could the critiques. He maintained that “political axe-grinding” was a prominent element in various reports to Congress, and that the “discount factor,”which apparently referred to methodology the CIA employed, “arbitrarily cut as much as 75 percent from any pilot claims that came their way.” Furthermore, Correll refuted CIA figures by pointing out that during Commando Hunt campaigns, Hanoi imported between 4,500 and 8,000 trucks a year from the Russians and Chinese. “That does not necessarily validate the Air Force claims,”he said,“but it does indicate they are more supportable than the ridicule of the [CIA] critics would suggest.”

The irrefutable truth is that the Ho Chi Minh Trail lay at the heart of the war—for both sides. For the North, the trail embodied patriotic aspirations, and the epic struggle to build and traverse it became the central experience for an entire generation. The amalgamation of the North’s stupendous efforts to open and sustain the trail, along with massive American aerial and technological attempts to shut it down, conveys a heroic yet tragic story.

From 1959 through early 1975, many thousands of NVA soldiers and workers perished along the trail, either from disease or as a result of air attacks. In spite of the losses, North Vietnam’s resolve never wavered. Hanoi, with focused national purpose, pushed 1.75 million tons of supplies down the trail, along with about a million soldiers. How much and how many actually arrived is still a matter of debate, but regardless the North Vietnamese experienced a fearsome loss in men and materiel.

By comparison, the U.S. efforts to interdict the trail cost billions of dollars annually. All told, American fighter-bombers flew 426,000 sorties over the roughly 2,000-square-mile sector of the trail running down the southern Laotian panhandle, with B-52s adding 30,000 more. The valor and dedication of the aircrews who flew those dangerous strike missions are legendary: 497 fixed-wing aircraft fell to NVA guns over Laos, at least 200 helicopters went down and almost 500 Americans are still missing in the Laotian jungles.

Yet despite all the airstrikes and the reams of statistics, and notwithstanding the spectacular results achieved at one-off locations such as the Covey Bomb Dump near Ban Bak, Laos, the Commando Hunt campaigns against the trail from Nov. 11, 1968, to March 29, 1972, never really succeeded. They ultimately became a protracted technological/ statistical crusade in which top military and civilian leaders interpreted the truck count to suit their own predetermined notions of victory. The bitter truth was that aerial interdiction against the Ho Chi Minh Trail failed to break the enemy’s will. In his memoir White House Years, Henry Kissinger perhaps came closest to explaining the failure when he observed,“It was a splendid project on paper.”


During his two tours as a forward air controller, Tom Yarborough flew more than 600 combat missions and earned numerous decorations, including the Silver Star. He currently teaches history at Northern Virginia Community College and is the author of the critically acclaimed book Da Nang Diary.

Originally published in the October 2013 issue of Vietnam. To subscribe, click here.