The Vietcong excelled in tunnel construction. The guerrillas dug impressive tunnel complexes under villages, between villages, and beneath their base camps. Some tunnel systems, including the famous Cu Chi tunnels northwest of Saigon, were decades old by the time American troops landed in South Vietnam in mid-1965.
Large tunnel complexes, such as the one below the timbered Iron Triangle, became something akin to a massive underground base camp, with storage areas, ammunition dumps, hospitals, and sleeping quarters. A U.S. Army study noted, “Generally, enemy tunnels were of two kinds: simple, shallow structures, hastily built and used primarily by local Viet Cong and guerrillas, or well-constructed systems used by large forces and usually found in uninhabited areas.”
The Vietcong went deep into the earth. It wasn’t uncommon for tunnels to extend 30 or 40 feet down. The deepest tunnels were impervious to the U.S.’s 250-lb. and 500-lb. bombs. Communist engineers excavated underground rooms with “A” frame roofs, which strengthened the caverns against the concussive power of high explosions. Tunnels contained multiple levels that could be entered through trap doors. Designing tunnels with multiple levels and trap doors limited the spread of tear gas, which the Americans pumped into the tunnel complexes to force the guerrillas to the surface or to suffocate them. Trap doors also blocked the smoke that might enter the system from surface fires or bomb explosions.
The Vietcong did not dig straight, horizontal tunnels. Subterranean pathways bore through the earth in an arch. This design feature diminished the killing range of explosives and gunfire. For example, an American tunnel rat could not just shoot straight down a tunnel and hope to kill a fleeing guerrilla. Instead, his bullet would eventually smack up against the curving wall of the tunnel, as would fragments from an exploding grenade or bomb. Vietcong guerrilla Tran Thi Gung remembered, “When G.I.’s discovered tunnel openings they dynamited them, but the tunnels were so deep and had so many twists and turns, they couldn’t do too much damage. It was like an underground maze. Most of the tunnels were just wide enough to crawl through and so cramped. There were only some places where you could sit up, never mind stand. Most of the time we lived in the dark…one time I was stuck in a tunnel for seven days and seven nights while the Americans were constantly bombing us.”
Wherever possible, the tunnels passed through non-porous clay – which absorbed the shock waves from exploding bombs and shells and kept monsoonal rains from collapsing the structures. Tunnel systems had multiple entry and exit points to ensure that the occupants could escape if Allied troops or bombs closed one or more of the other openings. Multiple air shafts extended from the earth’s surface to the dark, dank rooms and tunnel passageways below. This redundancy offered safety against suffocation if the Americans discovered a shaft and plugged it. False exits and fake entryways led American tunnel rats – the name given to the G.I.’s who had the nerve-wracking job of exploring the tunnels – to dead ends or booby-trapped rooms and booby-trapped doors.
G.I.’s expressed a grudging admiration for the Vietcong’s tunnelling capabilities. U.S. Army Captain John Cook recalled, “The amazing thing about the tunnel system was that you could walk over an area any number of times deliberately looking for a tunnel entrance, you’d never find it, because they were masters at disguising it. They would build the tunnel opening into the grass, into the surrounding terrain. The only way we ever found the entrance to a tunnel was someone pointed it out to us.” Gerry Schooler, who served with the 25th Infantry Division at Cu Chi recalled, “The tunnels were interesting. You could see how much work they put into them. That’s when I first realized that these people were not lazy, that they were industrious and dedicated…It was obvious they were dedicated and had been there for a lot longer than one or two years: these tunnels were big, complicated, and old.”
Long-occupied Vietcong areas were honeycombed with tunnels. In early 1967, when the Americans attempted to clear the Vietcong out of the Iron Triangle, G.I.’s discovered the extent of Vietcong tunnelling in the area. Jonathan Schell, who travelled with U.S. forces on the mission to clear out the Triangle wrote, “American intelligence had also received reports of a twelve-mile tunnel running the length of the Triangle from north to south.” Long tunnels such as the one traversing the Triangle allowed the Vietcong to move undetected from their base areas toward U.S. and South Vietnamese positions.
Because of the extensive tunnel systems throughout South Vietnam, the Americans found it difficult to clear and hold Vietcong areas, let alone find and kill the Vietcong. On countless occasions during the long war, G.I.’s believed they had cleared an area of the Vietcong only to learn later that the guerrillas had returned to the same area not long after the end of the U.S. operation. This was because the Vietcong simply re-emerged from their subterranean sanctuaries after the G.I.’s had departed.
The web of tunnels in War Zone D and the Iron Triangle impeded the clearing and holding of those regions. Despite the herculean attempts of the Americans to push them out, the Vietcong remained in both of those base areas until the end of the war in 1975. As an Army historian acknowledged in the early 1970s, “One such complex used by the Vietcong in the III Corps Tactical Zone was probably as much as twenty years in the building. Constructed in impervious layers of hard clay at varying depths, with small, well-camouflaged entrances, these tunnels defied any simple method of destruction.”
Journalist and historian S.L.A. Marshall once encountered a large tunnel system in a long-held Communist area. He admitted this tunnel complex prevented the Americans from effectively clearing the region. He wrote, “Trung Luong [village] was served by one of the most extensive tunnel system anywhere in the country. Of this came the enemy mobility that had cost Furgeson so many of his soldiers [54 casualties in two days]. The NVA had been moving through the catacomb to get from one firing point to another. Without this tunnel system, the air and artillery might have broken the resistance, but the heaviest bomb could not cut through to the tunnels.”
G.I.’s admitted that “Victor Charlie” owned the night, while the Americans owned the day. It was also true that while the Americans owned the surface of the earth (at least where they stood) Charlie ruled the subterranean realm. That dark, unseen world unnerved the majority of G.I.’s, few of whom wanted to enter it to contest the Vietcong’s hold on it. To American soldiers, the tunnels were mysterious, full of danger, and horribly claustrophobic. Big 19-year-old corn-fed Iowa boys did not even fit in the narrow, tight tunnel entryways. And the tunnels negated what the G.I.’s valued most in the war zone – speed, firepower, and open fields of fire. Down in the tunnels, the Americans were at a disadvantage against the small, agile Vietnamese.
Frederick Downs, who served with the U.S. Army at Duc Pho, Quang Ngai Province, in late 1967, recalled that the Americans had all but conceded the underground domain to the Vietcong. After discovering a vast tunnel network in rural Quang Ngai, Downs wrote, “None of us was going to lower himself to the bottom to explore the tunnels, so I called Delta Six [his commander] to report the find. We were not too concerned since Vietnam must have had a million miles of tunnels under everything. I had only been in-country a short time and already tunnels were a feature of the landscape.”
Downs should have been concerned by the Vietcong’s “million miles of tunnels.” Those tunnels made it difficult for the Americans to find the Vietcong, attain a high body count, and clear and hold the countryside. Tunnels impeded the achievement of General Westmoreland’s war aims. The presence of miles and miles of tunnels may even have precluded the possibility of the U.S. and South Vietnamese Army from ever pushing the Communists entirely out of South Vietnam or of winning the war. If the Vietcong’s underground empire could not be destroyed, the Americans had no way of completely securing South Vietnam’s surface territory. The inability of the Americans to hold the land was most apparent when the Vietcong succeeded in maintaining tunnel complexes, and a military presence, immediately adjacent to major U.S. bases.
At several locations in South Vietnam, Vietcong tunnels extended to the perimeter, and sometimes under the perimeter, of U.S. bases. At the 25th Infantry Division base at Cu Chi, the Vietcong burrowed under the perimeter wire, entered the base from below, and launched attacks on unsuspecting U.S. troops who had thought themselves safe inside the massive U.S. facility. At Danang, the Vietcong tunnelled into Marble Mountain, only a few miles south of the gigantic U.S. airbase. From the heights of the mountain, the guerrillas observed the comings and goings of the Marines and U.S. aircraft stationed at the base. The Vietnamese village of Dong Binh sat next to the gigantic U.S. base at Chu Lai. The Vietcong infiltrated Dong Binh. Overtime, the guerrillas developed a tunnel system under the village, which made it possible for them to enter and leave Dong Binh unobserved by the Marines on the nearby base. Most importantly, Dong Binh’s tunnels allowed the Vietcong to spy on the Marines on the base.
Tunnels, like the one under the base at Cu Chi, enabled the Vietcong to launch surprise attacks on U.S. bases. Those same tunnels allowed the guerrillas to make good their escape once the fighting tapered off. On countless occasions, G.I.’s recalled that during battle, the Vietcong suddenly broke off contact and slipped away. It was as if the guerrillas had disappeared into thin air. The Vietcong did disappear, but not into thin air. Rather, they had gone underground.
The Vietnamese use of tunnels symbolized the profound connection between the Vietnamese people and their land. Inside the tunnels, the land embraced the guerrillas, offered them succour, and preserved their lives. And thus, by keeping them safe, the land helped the Vietcong win the war.
 Robert R. Ploger, Vietnam Studies, U.S. Army Engineers, 1965-1970, (Washington DC: Department of the Army, 1989), 94.
 Christian G. Appy, Patriots: The Vietnam War Remembered From All Sides, (New York: Viking, 2003), 17.
 Ron Steinman, The Soldiers’ Story: Vietnam in Their Own Words, 1999, Reprint, (New York: Barnes and Noble Books, 2002), 226.
 Eric M. Bergerud, Red Thunder, Tropic Lightning: The World of a Combat Division in Vietnam, 1993, Reprint, (New York: Penguin Books, 1994), 192-193.
 Jonathan Schell, The Village of Ben Suc, (New York: Alfred A. Knopf, 1967), 18.
 Ploger, Army Engineers, 92.
 S.L.A. Marshall, The Fields of Bamboo: Dong Tre, Trung Luong and Hoa Hoi, Three Battles Just Beyond the South China Sea, (New York: The Dial Press, 1971), 121.
 Frederick Downs, The Killing Zone: My Life in the Vietnam War, (New York: W.W. Norton and Company, 2007), 95.
 Bing West, The Village, (New York: Pocket Books, 2003), 301.
 James William Gibson, The Perfect War: Technowar in Vietnam, 1986, Reprint, (New York: Atlantic Monthly Press, 2000), 123.