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Surprise attacks by elite Communist units known as sappers were one of the most serious—and feared—threats to Americans in Vietnam.

In the fog-shrouded early morning hours of March 28, 1971, 50 members of a specially trained North Vietnamese Army assault force, their bodies covered with charcoal dust and grease that made them almost invisible in the dark, quietly approached Fire Support Base Mary Ann, a small U.S. Army encampment in Quang Tin province in the northern part of South Vietnam. The remote outpost with about 30 buildings, including bunkers and sleeping quarters, was defended by 231 Americans of the 196th Light Infantry Brigade, 23rd Infantry (Americal) Division, along with 22 South Vietnamese soldiers.

The garrison had become lax about basic security measures, partly because of infrequent contact with the enemy, according to a post-battle interview with John Patrick, an infantryman with C Company, 1st Battalion, 46th Infantry Regiment, attached to the 196th Brigade.

The intruders, from the 2nd Company of the 409th NVA Main Force Sapper Battalion, crouched low in three- and six-man teams, silently slipped through the barbed wire that marked the firebase’s outer defenses. Under an umbrella of NVA mortar fire, the sappers raced through the compound tossing gas grenades and canvas satchels loaded with explosives. They then directed automatic weapons fire at the demolished or burning targets. The infiltrators hit the battalion tactical operations center and C Company’s command bunker, killing Captain Richard V. Knight, the company’s leader. Grunts were shot down trying to escape their quarters or buried alive when enemy explosives were hurled into their hooches. The base “was a shambles…with things burning all over the place,” wrote the Americal commander, Maj. Gen. James L. Baldwin, in a letter to his family. After one hour of close-quarter combat, 30 Americans were dead and 82 wounded. A count of the enemy dead showed 15 NVA bodies in and around the camp.

The attack was a stark example of the effectiveness of the sapper force. The sappers who so devastatingly struck firebase Mary Ann—as well as hundreds of minor outposts, major bases, airfields, fortified hamlets and large cities throughout South Vietnam—were members of the Bo Doi Dac Cong (roughly translated “soldiers in special forces”), a highly organized, well-trained and well-equipped organization that carried out special operations.

Americans called them “sappers,” from the French saper, a word meaning to undermine or weaken, typically by digging. In military usage, the term originally applied to French soldiers who dug narrow trenches, or “saps,” toward an enemy fort to provide a somewhat protected channel for moving men and artillery closer to the fort in preparation for an assault. Today, “sapper” refers more broadly to combat engineers who handle a variety of construction and demolition duties.

In Vietnam, however, American troops used the name primarily for North Vietnamese Army and Viet Cong units that broke through defensive lines using tactics more akin to raids by commandos than to the work of engineers.

North Vietnamese President Ho Chi Minh set forth the official requirements for sappers during an October 1969 military conference: “Adoption of sapper tactics must be flexible. Acquaintance must be made with combat techniques. Morale must be stable. Discipline must be strict. Determination to win and destroy the enemy must be strong. Be loyal to the party and the people. Accomplish all missions and overcome any difficulties.”

Even though loyalty to the Communist Party was a requisite for sapper selection, party membership was not. Because a large sapper force was needed, lip-service loyalty was good enough. Most sapper officers and noncommissioned officers were party members, however.

Bravery and ingenuity were paramount personality traits, since recruits would be operating in enemy territory against a more powerful force. Other important attributes were high intelligence, discipline and the organizational skills to operate independently in combat. But a kamikaze mindset was not prized. Highly trained sappers were too valuable to be thrown away on suicide missions. They were taught to complete their missions and return alive.

“Sapper fighting is a living symbol of our national character and soul, our indomitable fighting will, our creative energies,” Colonel Bach Ngoc Lien, a senior NVA sapper commander, wrote in a Communist Party newspaper, Nhan Dan, in December 1979. “Sapper fighting is the essence of Vietnam.” The premise behind it, he added, is “to allow the few to fight the many; the weak to fight the strong.”

Although sapper combat appears almost identical to classic guerrilla warfare, the North Vietnamese saw it differently. In guerrilla warfare, a small unit attacks and destroys a small isolated enemy formation. In a sapper operation, a small well-trained command attacks a post held by a numerically superior (although still somewhat small) force that is inside the enemy’s lines. The Vietnamese called this type of combat the “blooming lotus” tactic—penetrating a fortified area and assaulting outward.

Sappers generally did not attack enemy troops that were moving around in the field. The maneuvers of those units were unpredictable, and sappers wanted ample time to conduct thorough reconnaissance of an enemy position. In addition, experience showed that withdrawal from a field fight was more difficult than withdrawal from an urban area or firebase.

Before the Communists’ Tet Offensive against targets all across South Vietnam in early 1968, the sappers in the South were controlled by the Viet Cong and operated independently of the NVA. But after the horrendous losses the Viet Cong suffered during Tet, all sapper operations in South Vietnam were supervised by the 429th Sapper Group, which reported directly to the Sapper High Command, a department in the NVA High Command in Hanoi.

The NVA High Command devised the training program. After 1968 training centers in South Vietnam and Cambodia were run by the 429th Sapper Group, while the centers in North Vietnam and Laos were directed from the NVA High Command. The instruction could last from three to 18 months, depending on whether trainees would be soldiers in a regular unit or raiders operating outside a formal military structure.

Political indoctrination, carried out by party officials or commissars, was an important part of the program, but reconnaissance and observation skills were stressed the most. Sappers were taught to use a map and compass and learned how to spot enemy defensive positions, guard routines, command centers, fuel depots and ammunition dumps. They also were shown camouflage methods and practiced tiptoeing, duck-walking, crawling and other techniques to avoid detection when moving across hard ground, grassy fields, sandy areas, mud, swamps and water obstacles. They learned to disable mines and maneuver through barbed or concertina wire. There were classes in bomb making and close-combat infantry fighting.

The NVA and Viet Cong both had three sapper branches: naval, urban and field. Naval sappers attacked water supply routes and coastal installations. Urban sappers hit enemy positions in cities, spread propaganda, conducted sabotage operations and gathered intelligence. Field sappers, the largest branch, had two missions: infiltrate U.S. and South Vietnamese installations to destroy targets such as command posts, artillery positions and ammunition dumps; and train conventional infantrymen in perimeter penetration and shock attack.

Sapper assaults normally heralded an attack by regular NVA or Viet Cong forces. Sappers sometimes participated in conventional infantry assaults. Their support usually entailed breaching a defensive line and creating a gap the regular infantry could flow through. Unfortunately for the sapper detachments involved in those missions, the sustained fighting of a conventional battle would often further thin ranks already being depleted from the sappers’ traditional commando activities.

Field sapper organizations established by the Viet Cong ranged from independent squads to battalions. The NVA field units were grouped into battalions and regiments. The standard battalion had a headquarters platoon of 15 to 20 men and three field companies of 60 members each. Every company was divided into three 20-man sections. A section comprised six cells of about three men each. Rounding out the battalion would be a signals platoon of 30 soldiers and a reconnaissance platoon with 30 men.

Some sapper units were heavily armed, with even more firepower than conventional NVA infantry units of a similar size, while other outfits sported the bare basics in weapons. The most common weapons in a field sapper’s arsenal included AK-47 assault rifles and TNT satchel charges. Other weapons included B40/41 rocket-propelled grenade launchers, bangalore torpedoes, Soviet-made RPK light machine guns, various hand grenades, mines, pistols and submachine guns. Several units had a heavy weapons section equipped with 57mm and 75mm recoilless rifles, 60mm or 82mm mortars and flamethrowers.

Before conducting a mission, sappers carried out a thorough reconnaissance. They not only scouted the target from the outside, using sources such as local guerrillas, but also collected intelligence using agents operating from the inside. Just before the attack on firebase Mary Ann, the Americans were warned that some of the firebase’s South Vietnamese soldiers, supposedly allies, were secretly working as NVA operatives. That may have been the case. During the battle, U.S. troops took fire from South Vietnamese army positions inside the base, and the sappers did not assault those sectors.

After a final reconnaissance was made, usually over three to seven days, the sapper commander could determine which enemy fighting positions and other obstacles his men would face. He then planned the attack. A typical raiding party, without infantry support, would be organized into four elements: security, assault, fire support and reserve.

The security team consisted of a reinforced cell (four men), armed with at least one RPG launcher, AK-47s and several mines to stop enemy reinforcements from reaching the battlefield.

The key component of the raiding party was the assault element, two or more teams called “arrows.” Moving along a specified route, each arrow traveled with three cells—contingents for penetration, assault and direct-fire support. The penetration cell had four members, usually wearing only shorts and a coat of mud, who carried AK-47s, wire cutters, bamboo poles to lift up barbed wire, bangalore torpedoes and probing tools such as metal stakes, knives and bayonets. The assault cells, hauling most of the demolition material, employed four or five men loaded with AK-47s, RPGs, anti-tank grenades and scores of explosive charges. Often more than one assault cell was used in an operation. The direct-fire support cell, made up of two or three soldiers, brought RPGs and AK-47s to the assault.

The assault team also received assistance from indirect fire laid down by another support team. The 30-man indirect-fire crew, using 60mm or 82mm mortars and AK-47s, masked the noise made by sapper penetration units as they began their infiltration, distracted the enemy’s attention from the perimeter section where the assault team was operating and hit enemy forces trying to react to the attack. That crew was guarded by its own security cell.

The reserve element, usually a reinforced infantry squad (13 men), furnished close-in support when needed. Its armament would consist of a machine gun, an RPG launcher, AK-47s and a dozen or more explosive charges.

In the planning process, the raid’s commander would determine the approach, infiltration and withdrawal routes, fire support positions and target priorities. He would then organize rehearsals that used maps, mock-ups and diagrams of the target area in drills that might last days. An attack’s success also depended on the element of surprise, which was the only thing that could give the sappers an edge against the massive American firepower. To attain that advantage, sapper commanders emphasized camouflage, stealth, speed of execution and—as at firebase Mary Ann—lulling the garrison into assuming an attack would not occur.

Sapper missions for a late-night attack began at dusk because it might take six or seven hours of slow, cautious movement to cover the last 200 yards without detection. Sappers normally chose the most difficult avenue to the base hoping the enemy would not expect them to take that approach.

When they reached the defensive barriers, sappers preferred to cut through the barbed wire rather than detonate explosives, which would give away their position. To draw the defenders’ attention away from the penetration, the indirect-fire element might use diversionary feints, such as artillery shelling to make the garrison think it was under a routine attack launched just to test its defenses. In response, the troops would take cover in their bunkers.

If the penetration force was prematurely discovered or pinned down by enemy fire, the assault cells would use RPGs to speed up the attack, while the penetration cell would start throwing explosives in all directions in a last-ditch attempt to blast through the perimeter.

Once inside, the sappers moved rapidly. They placed demolition charges on key installations, threw satchel charges and grenades, and fired RPGs to inflict casualties, suppress enemy resistance and keep the garrison’s troops confined to their bunkers so they could not organize defensive fire or counterattacks, as at firebase Mary Ann.

The attacks did not always come off as planned. In June 1969, during a move against Marine firebase Charlie One just below the Demilitarized Zone, NVA sappers were hit with shelling from South Vietnamese artillery before they reached the base’s outer wire. The indirect-fire element mistook the 105mm enemy guns for the detonation of their comrades’ sapper charges and withheld its fire. The sappers, without the benefit of any covering fire, were mowed down in the open, and 67 died.

After the sappers finished their assignment (the optimal completion time was 30 minutes) or if they could not overcome enemy opposition, the raiding party withdrew, covered by the direct-fire support and reserve sections. They moved back through the penetration lanes to a rallying point.

North Vietnamese and Viet Cong sappers faced a foe with tremendous superiority in technology, firepower and troops, yet they destroyed hundreds of supply and fuel depots, military bases and pieces of equipment, killing and wounding many troops in the process. Their sudden and unexpected attacks also created a fear that no place—no matter how well fortified and well armed—was safe from a sapper assault.


Arnold Blumberg, an attorney in Baltimore, served in the Army Reserve 1968-74, ending his term as a staff sergeant in a maintenance company. He writes on military topics for history publications.

Originally published in the April 2015 issue of Vietnam. To subscribe, click here.