You take the rifle off your shoulder and hand it to somebody. You take off your helmet, your web gear, your rucksack. You keep the .45 pistol, a flashlight, maybe a knife. And then you get on your hands and knees and you lower yourself into a space that was built for people who averaged about 5’2″ and 110 lb. And you are almost certainly bigger than that.

Sergeant Ronald Payne was 21 years old from Atlanta, Georgia. He served with the 196th Light Infantry Brigade in 1967. In January of that year, during an operation in the Hobo Woods northwest of Saigon, Payne’s unit found a tunnel complex. Payne went in with a silencer-equipped revolver and a flashlight. What he found down there were detailed maps and operational plans of the Viet Cong.

 He also found guerrillas ahead of him in the dark, moving away from his light, and he fired at them. When the famous photograph was taken, Payne emerging from the tunnel mouth, squinting in the sunlight, revolver in hand, he’d already been underground long enough that his eyes had adjusted to the darkness. And the daylight hit him like a blow.

That photograph is one of the most reproduced images from the Vietnam War. But it only shows the end of the story, the coming out. What it doesn’t show is the going in. And the going in is the part that mattered. Because once you went down, everything that was true on the surface stopped being true. The Cu Chi tunnel system ran for over 150 miles in Binh Duong province, northwest of Saigon.

 It had been under construction since the late 1940s, expanded through the French war, and by the time the Americans arrived, it was a military installation with multiple levels connected by narrow passageways, sharp turns, and vertical shafts. Some sections were barely 2 ft wide and maybe 3 ft high. The Viet Cong could move through them crouched or on all fours.

An American soldier, even a small one, often had to belly crawl. When the 25th Infantry Division set up its base camp at Cu Chi in early 1966, the division literally built on top of the tunnels. For weeks, Viet Cong fighters came up through trap doors inside the American perimeter, launched attacks, and disappeared back underground.

The army tried everything to clear them out. Tear gas, acetylene gas pumped in and ignited, explosives dropped down the shafts. None of it worked reliably because the tunnels were designed with gas traps, sections that could be sealed off with underwater U-bends or clay plugs, and the VC could isolate a section, let the gas dissipate, and reoccupy it within hours.

The army figured out pretty quickly that the only way to know what was down there was to send a man. Tom Mangold and John Penycate, the BBC journalists who wrote the definitive account of the tunnel war, learned something surprising when they began interviewing Viet Cong veterans. The VC admired the tunnel rats.

 They considered them the best American soldiers they’d faced. That’s not a compliment the VC handed out easily, but the men who fought underground, alone, with pistols, the VC understood what that took because they’d built the tunnels specifically to make it impossible. Here’s what it was like to go in based on the accounts collected by Mangold and Pennicate and on interviews with veterans like Nick Sansa and C.W.

Bowman. The entrance was usually a small hole sometimes concealed under a cook pot or a pile of leaves or built into the floor of a hut. You dropped through it into a shaft that might go down 4 or 5 ft before leveling out into a horizontal passage. Some shafts were angled which meant you went in headfirst on a slope arms extended in front of you and if anything was waiting at the bottom you met it face-first with no way to back up fast enough to matter.

Once you were in the horizontal passage you moved on your elbows and knees. The floor was packed earth hard and smooth from years of use. The walls were close enough that your shoulders brushed both sides in the tighter sections. The ceiling was close enough that if you raised your head you hit it. The air was hot 100° or more with almost no circulation.

Humidity was total. Within minutes your clothing was soaked through and the combination of sweat and loose dirt turned you into a clay figure. Your flashlight was your lifeline but it was also the single thing most likely to get you killed because in a straight section of tunnel a flashlight beam could be seen from 50 or 60 yd and anyone waiting in the dark with a weapon would see you long before you saw them.

So the tunnel rats developed techniques. You flicked the light on scanned for maybe 2 seconds then killed it and moved to a different position before turning it on again. You never stayed in the same spot after using the light. You listened between flashes for breathing for the scrape of cloth on earth, for the clink of metal, for anything that didn’t sound like the tunnel settling.

 Some rats eventually switched to red-lensed flashlights, which preserved more of their night vision, and didn’t carry as far in the dark. The Viet Cong only used white lights and candles, so a red glow in the tunnel meant American. Sanza, who operated as a tunnel rat with the Marines, described his preparation in detail. He wore black clothing.

 He covered his skin in mud. He ate the same food the Viet Cong ate, fish, rice, so his body odor wouldn’t give him away. He said he went weeks without showering, because even that kind of cleanliness could mark you as American in a space where smell traveled faster than sound. His equipment was a .38 caliber revolver with a silencer, a bayonet, a bamboo pole for probing the ground ahead of him, and a small camera to photograph anything he found.

He described the training he’d been given as “learning to hear with my eyes and see with my ears.” Which sounds like a riddle, but was actually a precise description of how the senses reorganized underground. In total darkness, you stopped trusting your eyes and started trusting things you’d never paid attention to on the surface.

The direction of the air current, the temperature change near an intersection, the difference between silence and the kind of silence that has something alive inside it. The booby traps were the thing that most accounts come back to. The VC wired the tunnels with trip lines made from old American communications wire.

 Thin, almost invisible, strung across the passage at the exact height where a man crawling on his elbows would catch it with his wrist or his chest. The line was connected to a grenade. Mangold described what a grenade did inside a tunnel without any exaggeration. The blast was entirely contained, bouncing off the walls, and the result was unsurvivable.

The tunnel rats probed ahead of them constantly, running their fingers along the floor and walls, feeling for the wire. One man described crawling with his hand extended in front of his face, fingers spread, inching forward in total darkness, knowing that if he touched the wrong thing, he wouldn’t hear the explosion.

Some traps weren’t explosive. The VC dug false floors over pits lined with sharpened bamboo stakes, sometimes smeared with excrement to cause infection. Scorpions and snakes were placed in sections where Americans were likely to reach blindly around corners. Whether the snakes were deliberately placed or just lived there because the tunnels were warm and dark is still debated, but the result was the same.

You could reach around a bend and put your hand on something that bit. The deeper you went, the worse your options got. That’s the part I want to make sure comes through because it’s the center of this whole story. Each turn you made, each shaft you descended, each section you cleared added distance between you and the surface.

The man at the tunnel entrance, your partner, >> [music] >> the one sketching a map based on what you called back, or the tugs you gave on a communications line, could only follow you so far. In the deeper sections, the line went slack or snagged on corners. Voice didn’t carry. You were alone in a way that no other job in that war replicated.

 Not a patrol alone in the jungle. Not a point man ahead of the column. Truly alone, underground, in a space built by the enemy, with no room to turn around. And what you found down there could be anything. The tunnels weren’t just hiding places. They were functioning military installations. Some complexes had hospitals, mess halls, weapons factories, printing presses, and command centers.

During one operation, tunnel rats found 6,000 lb of rice and 40 lb of salt stored in a 120-ft tunnel. On another, they discovered a missing M48 tank that the Viet Cong had somehow gotten underground and were using as a command post. In 1970, tunnel rats found a signals intelligence operation where Viet Cong code breakers had been intercepting and decoding every radio transmission from the 1st and 25th infantry divisions.

Every patrol order, every fire mission, every medevac call, the VC had been reading all of it. The discovery of that node immediately made both divisions safer because the enemy lost the ability to set deliberate ambushes based on American communications. But, somebody had to crawl through a hole in the ground with a pistol to find it.

Turning around was the practical problem that nobody above ground fully understood. In a passage 2-ft wide and 3-ft high, you cannot reverse direction. You can’t spin your body. You have to back up the way you came in, which means crawling backward blind through every section you’ve already cleared, hoping that nothing has changed behind you.

Because the VC had a tactic for that, too. They’d let the tunnel rat pass through a section, then quietly seal it behind him with a clay plug, or occupy a side chamber he’d already checked. When he tried to come back, the tunnel wasn’t empty anymore. There’s a line from Mangold’s book that I haven’t been able to shake since I first read it.

A tunnel rat described what happened when the two of them, the American and the Viet Cong, found each other in the dark. He said that sometimes, after a long pursuit through a narrowing passage, he’d come around the corner and find a VC soldier just sitting there. Not hiding anymore. Just sitting and waiting.

And the tunnel rat said something that cut right through everything I’d read about the war. He said, “They were the ones you never killed. You just backed out and told them up above the tunnel was cold.” Cold meant empty. It was the word you used when the tunnel had no enemy in it. And this man was saying that sometimes, when he found someone down there who wasn’t running, who wasn’t fighting, who was just sitting in the dark waiting for whatever was going to happen, he chose to come back up and lie.

He called the tunnel cold because whatever he saw in that man’s face, in that darkness, at that distance, was something he didn’t want to bring to the surface. I don’t know his name. Mangold didn’t identify him. What I know is that the tunnel rats as a group never became an official military occupational specialty.

There was no formal designation, no special unit patch, no distinctive qualification badge. They were infantrymen who volunteered or were selected because they were small enough to fit and steady enough to function in a space that most human beings cannot tolerate. The 25th Infantry Division, the 1st Infantry Division, the 196th Light Infantry Brigade, and several other units all used tunnel rats at different points in the war.

Some of them became legends within their units. Sergeant Robert Batten of the 1st Infantry Division was known as Batman. He led a team of eight tunnel rats in the Iron Triangle, and he was apparently so effective that the Viet Cong put him on their most wanted list. The only sergeant on a list otherwise composed entirely of generals.

During one operation, Batton’s team worked a tunnel complex for three straight days. On the first day, they flushed out and captured five Viet Cong. On the second, three were killed, four captured, and 15 more fled to the surface. On the third day, Batton was injured and couldn’t continue.

 But his men pushed past him and went deeper, eventually driving over 150 enemy soldiers out of the tunnels. That’s the kind of sustained underground combat that most people can’t even picture because we don’t have a frame of reference for fighting in a space where you can’t stand up. The techniques they developed, the red flashlights, the probing ahead, the mud on the skin, the three shot rule where you never fired more than three rounds before reloading so the enemy couldn’t rush you during a magazine change.

All of that was passed from man to man, not written in any manual until later. When they came out, they whistled. That was standard practice. You whistled a tune that had been agreed on before you went in so the men at the entrance wouldn’t mistake a mud-covered figure emerging from a hole in the ground for a Viet Cong guerrilla and shoot him.

Ronald Payne came out of the Hobo Woods tunnel squinting against the light. Nick Sanza came out of his tunnels still hearing his own breathing in the dark. C.W. Bowman came out and kept going back in because once you were the man who did it, you were always the man they sent. Bowman said later that the thing he carried wasn’t fear.

It was sound. He could still hear the tunnel, the close, muffled silence that pressed against his ears when the flashlight was off and the air was thick and the darkness had weight to it. “That sound,” he said, which wasn’t really a sound at all, but the absence of every sound he’d ever known, stayed with him for the rest of his life.

Not the traps, not the enemy, the quiet.