A couple weeks ago I stopped by the National Museum of the United States Air Force, and one section on the Vietnam War really caught my attention. Obviously, the F-4 Phantom II is the kind of aircraft that makes you stop and stare, but what actually pulled me in was a small plaque about the tunnellers, specifically what they endured. It was the kind of detail that doesn’t get the spotlight, but probably should. So let’s get into two wars where tunneling wasn’t just a side note, it was a critical part of how the fighting was done.

If you thought World War I was all mud, machine guns, and trench foot, think again. Beneath the chaos, there was an entirely different war happening underground. Specialized units known as tunnellers, many of them former miners, were sent beneath no man’s land to dig toward enemy lines. These guys weren’t just shoveling dirt; they were working in pitch-black conditions, often lying on their sides, silently carving through clay with bayonets or modified tools so the enemy wouldn’t hear. One wrong noise, one collapse, or one counter-tunnel from the other side, and it was game over. The British formed entire tunneling companies under the Royal Engineers, while the Germans, who had a head start, were already masters of underground warfare. It became a deadly game of hide-and-seek played in total darkness, where the stakes were entire platoons.

The goal was simple in theory but terrifying in execution: dig under the enemy, pack the tunnel with explosives, and detonate it to wipe out trenches from below. And when it worked, it really worked. The most famous example came in 1917 at the Battle of Messines, where Allied forces detonated 19 massive mines beneath German lines. The explosions were so powerful they were reportedly heard in London, over 100 miles away. In seconds, thousands of German soldiers were killed, and the landscape itself was permanently reshaped. But for every massive success, there were countless smaller, brutal underground encounters, close-quarters fights in cramped tunnels where soldiers used pistols, knives, and sometimes just their bare hands. It was war at its most claustrophobic and unforgiving, fought not just across the battlefield, but deep beneath it.

World War I proved you could fight a war underground, but decades later, in Vietnam, that idea got taken to a whole new level. This wasn’t about sneaking under enemy lines for a single massive blast. In the jungles of Southeast Asia, the Viet Cong turned tunneling into an entire way of life. Instead of short, tactical tunnels, they built sprawling underground networks that stretched for miles, with living quarters, kitchens, storage rooms, hospitals, and hidden entrances that could be right under your feet without you ever knowing. Places like the Cu Chi Tunnels became full-blown subterranean cities, allowing fighters to disappear, regroup, and strike again seemingly out of nowhere.

For American forces, this created a completely different kind of nightmare. You weren’t just fighting an enemy, you were fighting the ground itself. That led to the rise of the “tunnel rats,” soldiers who volunteered (or got told) to crawl into these pitch-black passages armed with little more than a pistol, a flashlight, and nerves of steel. The tunnels were deliberately designed to be claustrophobic, barely wide enough to squeeze through, and filled with booby traps like punji stakes, tripwires, and hidden explosives. Unlike World War I, where tunnels were about engineering and demolition, Vietnam’s underground war was personal, close-quarters, one-on-one, and often silent. Every corner could be a trap, every shadow could be someone waiting.

What made it even more brutal was how the environment itself worked against you. Heat, humidity, insects, and lack of oxygen turned these tunnels into suffocating ovens. The Viet Cong knew the layout like the back of their hand, while U.S. soldiers were essentially navigating a maze blindfolded. There were no massive explosions like at Messines, no single moment that defined the underground war. Instead, it was a slow, grinding psychological battle where fear did as much damage as bullets. If World War I tunneling was about blowing the enemy off the map, Vietnam was about surviving inside the map, and realizing it might be trying to kill you.