The Israel-Hamas Tunnel War Will Be Like No Other

After her release from two weeks of Hamas captivity, 85-year-old Yochaved Lifshitz described being marched for several kilometers underground by her captors through “a giant system of tunnels, like spiderwebs.” Few other Israelis had seen the Gaza Strip’s storied tunnel complex, but many are now going to get the chance.

Israeli Defense Forces that pressed several miles into Gaza beginning last Friday are forced to contend with a sophisticated labyrinth of underground tunnels and bunkers constructed over several decades by Hamas, hiding fighters, weapons, and more than 200 Israeli hostages. The elaborate system is believed to extend for hundreds of miles and, in some locations, lies several hundred feet below ground. Military experts who have studied Hamas call the tunnels a formidable defensive system that would be incredibly costly for Israeli troops to neutralize, even after several weeks of heavy bombardment targeting the network.

Geographically, Gaza is militarily indefensible: a flat, low-lying expanse of arid coastal plain that measures just 25 miles long, four to eight miles wide, and surrounded by the sea and the militarized borders of Egypt and Israel. The IDF’s military superiority over Hamas is overwhelming with an air force, armored vehicles, artillery, and hundreds of thousands of troops deployed against a Hamas force of an estimated 30,000 to 40,000 fighters.

But the matchup becomes less lopsided when considering how Gaza’s dense urban landscape can negate many of the advantages of Israel’s high-tech military. Hiding in buildings and rubble, a relative few Hamas fighters can hold off vastly larger Israeli forces. Add a vast network of tunnels with widely scattered hidden entrances, and you’ve got an environment so challenging that it may not be possible for Israel to achieve its goal of destroying Hamas’s military capabilities.

“It’s the worst nightmare for the people that have to plan an attack and for the people that have to execute it,” says Walker Mills, a Marine Corps captain who has studied and written about tunnel warfare. In classic guerrilla-war fashion, the IDF has been drawn into a fight where its advantages are minimized and those of its opponents are maximized. “You’re entering an environment that the enemy has created. It’s inherently prepared for you to come in and for them to defend it.”

Gazans built some tunnels in the 2000s under the border with Egypt in order to smuggle weapons and goods, but the tunneling effort took on a whole new scale after 2006 when Hamas took power and began to build an extensive system of fortifications both above and below ground. The massive tunnel network, dubbed the “Gaza Metro,” is believed to be hundreds of miles long, possibly even longer than the 248 miles of the New York City subway.

Hamas diggers had the good fortune of a fairly deep water table and a soft substrate. “The geology is very conducive,” says John Spencer, chairman of urban-warfare studies at the Modern War Institute at West Point. Unlike the Hezbollah tunnels in the north of Israel, where the rock is so hard Hezbollah crews had to cut through it with diamond-tipped drills, tunnels here can be dug quickly using unskilled labor.

Based on its experience countering tunnels in previous conflicts, Israel is well acquainted with the basic features of the Hamas underground complex. A standard tunnel size is six and a half feet tall and three feet wide and lined with precast concrete shoring. Many are about 160 feet deep, but they’ve been found as deep as 230 feet — deeper than the deepest stations in the London Tube. According to one Reuters report, a half-mile-long tunnel takes six months to build. Sections of tunnel have different characteristics depending on what they’re used for. Some are wide enough for small vehicles and are equipped with electric lighting and plumbing. Others are damp, unlit, and barely wide enough to walk through. Larger chambers have been dug to accommodate workshops, generators, command posts, weapon-making workshops, and storage facilities. Underground reserves hold hundreds of thousands of gallons of gasoline and diesel fuel.

But the extent to which Hamas’s October 7 attack caught Israel off-guard raises questions about how good its intelligence about the tunnel network really is. “I think [the Israelis] are realizing that there’s just a much more extensive network than they were aware of,” says Mills. “Going into an environment where you really don’t have a good idea of what’s there is a nightmare for a military.”

In 2014, after Hamas kidnapped and murdered three Israeli hikers, the IDF invaded Gaza with the stated goal of destroying Hamas’s tunnel network. But the IDF found that it had been ill equipped to deal with the challenges of fighting underground. In one of the few published accounts of tunnel combat in Gaza, an Israeli sergeant described how he’d volunteered to enter a Hamas tunnel to see if it could be destroyed and had had to leave behind his standard-issue rifle and bulletproof vest and instead carried a flashlight, a camera, and a pistol. After spending an hour in the tunnel, and then returning a day later for a second check, he was able to gather enough information that the tunnel was destroyed. By the time the incursion ended a month later, 34 tunnels had been destroyed, but neither Hamas or its tunnel network was neutralized.

Still, the Israeli intelligence service Shin Bet learned where some of the tunnel network was located and how it was built. Israel gained some of the world’s best tunnel-detection technology, according to Spencer, such as sensors that listen for activity below the surface and ground-penetrating radar. But it’s questionable how effective these are against the most deeply buried sections of the tunnel system. “There’s a depth all technologies are limited to,” Spencer says. Since 2014, Israel has spent considerable effort building what are now considered to be the most advanced underground fighting capabilities in the world. It now trains all regular-army units in the fundamental concepts of tunnel warfare and has expanded a special-forces unit called Samur (“Weasel”) that specializes in infiltrating underground networks.

Once a tunnel is located, the question is how to destroy it. One tactic is to drop large bombs like the 5,000-pound GBU-28 “bunker buster” that Israel used extensively during an 11-day conflict in 2011, when Israel said air strikes destroyed more than 60 miles of tunnels. But this approach might not be viable in areas of Gaza where civilians remain.

Another option is to secure tunnel entrances and then seal them off or destroy them from within. To do that, Israeli forces will have to fight their way through an urban maze where attacks can come at any time from any direction — thanks in part to the tunnels that allow Hamas to move its fighters and weapons freely throughout the territory and to pop up to strike seemingly at random, even in areas that Israeli troops have already cleared. “In a battle like this, you can’t assume that any area is clear, even if you’ve been there for a long time,” says Spencer. “The soldiers are not going to ever be able to let their guard down. And even if they clear the house and anybody who goes back in that will have to clear it again. They’ll have to have their heads on the swivel 24 hours a day.”

The weakest point of any tunnel is the entrance. Once it has been captured, Israel has several ways of rendering the tunnel inoperative. In the past, Israel has sealed them up by filling them with concrete. But on the scale required in Gaza, this would be tremendously expensive, not to mention expose cement-mixer trucks to enemy fire. Recently Israel has begun using a new kind of weapon called a “sponge bomb.” A liquid chemical mixture is poured into a tunnel, where it expands into a foam that then hardens. This has the advantage of being lightweight enough to be carried deep inside a tunnel to seal off side entrances that Hamas fighters could use to launch ambushes.

None of these tactics will work if rescuing hostages is the priority. In that case, says Spencer, “IDF soldiers will have to enter tunnels and fight.”  But it’s not as simple as going underground. Fighting there  is a lot like fighting underwater, according to Mills, requiring both special equipment and special tactics.

“Things like that you take for granted, like your radios, are not going to work underground,” he says. “Your expensive night-vision equipment still relies on a little bit of ambient light, so it’s not going to work underground.” Instead of long rifles, the close quarters require short-barreled weapons with silencers to reduce the echo of the gunshot in confined spaces. Instead of bulky body armor, soldiers may instead carry ballistic shields. Specialized radio equipment is needed to function despite the shielding effect of the surrounding earth. Even the air can be an obstacle. Oxygen may be in short supply, and smoke or toxic gasses can be at dangerous levels, requiring soldiers to wear self-contained breathing apparatuses.

Tunnel-fighting troops are trained in tactics adapted to these conditions, such as reconnoitering ahead to detect booby traps and ambushes before moving in. “Before you go into a subterranean environment, you’re going to want to get as much information about it as you can,” Mills says. “Whether that’s so using drones, robots, or a dog with a camera on it, you want to get as good a look as you can before you go down there.” According to the U.S. Army’s tactical guide to underground fighting, units should take care to “never stop in a long, straight stretch of tunnel” where they would make for an easy target. If a unit finds itself in a firefight, it should deploy ballistic shields and keep some distance from walls and the floor “to reduce ricochet concerns.”

Soldiers in specialized tunnel-fighting units have to be psychologically screened owing to the unique pressures of the environment. “Not all soldiers can do tunnel warfare. Some of the best on the surface are incapable of entering a tunnel for psychological reasons,” Spencer says. “Some soldiers, under the stress of combat, will lose their sense of time and direction and really become incapacitated because of the cognitive aspects of being in that space.”

Mills, a former combat-platoon leader who dealt with tunnels in combat exercises, believes that the scale of the combat mission will mean that much of the fighting underground will have to be done by reservists with relatively little training or specialized equipment.  Even for units that do have advanced training and equipment, fighting at close quarters in tunnels is extremely dangerous. “We talk a lot about precision warfare,” says Mills. “Well, if you want to do precision warfare, you need precision intelligence. And if you don’t know what you’re going into and it has to be figured out by the guy at the front of the squad, it’s going to be a lot more costly.”

As a result, Israel is putting itself in danger of paying a larger price than it may ultimately deem worthwhile. By tradition, says Spencer, “the IDF is casualty averse. Everything they develop is about protecting their national treasure” — its people. The Merkava tank, for example, is one of the most heavily armored tanks in the world because crew survivability is such a high priority. But in the current Gaza invasion, he says, “they know they will lose a lot of casualties. It’s going to cost a lot. But it has to be done to accomplish this mission.”

The war, of course, will also create a lot of casualties on the other side. Gaza’s Health Ministry says that more than 8,500 Palestinians have already been killed in the fighting so far, a figure that far exceeds any previous Israeli-Palestinian conflict. Most of the victims were women and children, it says. That will not do Israel any favors in winning hearts and minds, either at home or around the world, where the massive protests that have sprung up against Israel’s war.

“They don’t really have any good choices,” says Mills of the Israelis. “It’s a tragedy and I think it’s going to get worse. I don’t see how they have other options than an invasion, but I also don’t see how it could logically lead to an improved situation.”