The Gaza Strip has all the harrowing pitfalls soldiers have learned to expect from urban warfare: high-rise ambushes, truncated lines of sight and, everywhere, vulnerable civilians with nowhere to hide.
But as Israeli ground forces inch their way forward in Gaza, the bigger danger may prove to be underfoot.
The Hamas militants who launched a bloody attack on Israel last month have built a maze of hidden tunnels some believe extend across most if not all of Gaza, the territory they control.
And they are not mere tunnels.
Snaking beneath dense residential areas, the passageways allow fighters to move around free from the eye of the enemy. There are also bunkers for stockpiling weapons, food and water, and even command centers and tunnels wide enough for vehicles, researchers believe.
Ordinary-looking doors and hatches serve as disguised access points, letting Hamas fighters dart out on missions and then slip back out of sight.
No outsider has an exact map of the network, and few Israelis have seen it firsthand.
But photos and video and reports from people who have been in the tunnels suggest the basic outlines of the system and how it is used. The source material includes photographs taken inside the passageways by journalists, accounts from researchers who study the tunnels, and details of the network that emerged from Israeli forces when they invaded Gaza in 2014.
Dismantling the tunnels is a key part of Israel’s goal of wiping out Hamas’ leadership in the wake of the Oct. 7 attack.
To do that, Israel’s forces will need to find entrances that are often hidden in the basements of civilian buildings, leading into concrete-lined tunnels, imagery suggests. They are typically just six and a half feet tall and three feet wide, experts said, forcing fighters to move through them single file.
One 85-year-old Israeli woman who was held hostage for 17 days in the tunnels after being kidnapped on Oct. 7 described being marched through a “spider web” of wet and humid tunnels. She eventually reached a large hall where two dozen other hostages were being held, she said.
There are still believed to be more than 200 Israeli hostages being held by Hamas, and many are likely in the very tunnels Israel aims to destroy. Prime Minister Benjamin Netanyahu has said that bringing them home is one of the two main aims of the invasion, the other being to “destroy Hamas.”
The tunnels used for hiding Hamas equipment and fighters are not the only hidden passageways in Gaza.
After Hamas came to power in 2007, and Israel tightened its blockade of the territory, an extensive network of smuggling tunnels grew under the border between Gaza and Egypt. These tunnels are used to circumvent the blockade and allow the import of a wide variety of goods, from weapons and electronic equipment to construction materials and fuel.
The Egyptian authorities have made extensive efforts to destroy these smuggling routes, including pumping seawater to flood the network and collapse many of the tunnels. But some smuggling tunnels are still believed to be in operation.
Although the Israeli military far surpasses Hamas’ in both size and equipment, fighting an enemy with its own network of tunnels is a high-risk undertaking.
John W. Spencer, who studies urban warfare at the U.S. Military Academy’s Modern War Institute, describes it as more like “fighting under the sea than it is on the surface or inside of a building.”
“Nothing that you use on the surface works,” he said recently on the Modern Warfare Project podcast. “You have to have specialized equipment to breathe, to see, to navigate, to communicate and to deploy lethal means, especially shooting.”
One of the main dangers of going into the tunnels is that Hamas has booby-trapped the entrances with explosives, experts say.
“The moment they realize the Israelis have entered the tunnels, they will just press the button and the entire thing could collapse on the Israelis,” said Ahron Bregman, a senior teaching fellow at King’s College London who specializes in the Arab-Israeli conflict.
Israeli forces will probably not be able to destroy the entire tunnel network.
“It is just too big, and there’s no point in dismantling all of it,” said Dr. Bregman. Instead, they will focus on blocking the entrances to the tunnels, likely by calling in airstrikes, or having engineers destroy them with explosives.
They are also unlikely to take their fight underground — unless they believe they have no other choice.
Entering the tunnels would strip Israeli forces of their advantages, Dr. Bregman said. At the moment, the Israelis are making headway with a mass of troops, tanks and helicopters.
“The moment you get down to the tunnel, it is one against one,” he said.