A MARTÍNEZ, HOST:
As Israel pushes into Gaza with a ground offensive, one of its biggest challenges will be dealing with a vast underground tunnel system Hamas uses for its military operations. It's something they've tried to do in the past without success, and it puts civilians at risk. NPR's Jackie Northam reports from Jerusalem.
JACKIE NORTHAM, BYLINE: Israel's military calls it simply the Gaza metro, a labyrinth of Hamas tunnels winding underneath fields, schools, mosques and hospitals in Gaza.
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NORTHAM: This video by the Israel Defense Forces shows armed Hamas militants moving quickly through tall tunnels, before emerging from a barely noticeable hole in the ground. A Hamas leader proclaims the militant group has hundreds of miles of underground tunnels.
DAPHNE RICHEMOND-BARAK: This is where they keep their ammunition, their weapons, their rocket launchers. This is where they have their command and control centers.
NORTHAM: Daphne Richemond-Barak is a specialist on tunnels at Tel Aviv's Reichman University and wrote a book called "Underground Warfare." She says tunnels in Gaza have been around for decades, but she says they turned into a strategic threat in 2014 when the militants used them for surprise attacks.
RICHEMOND-BARAK: Israel really took full measure, I think, in 2014. That was a wake-up call for Israel, but not just a wake-up call, it also led to a change of strategy.
NORTHAM: After that, Israel began studying ways to better detect, map and seal off tunnels. In 2021, during another conflict with Hamas, Israel said it took out more than 60 miles worth of tunnels. But Lenny Ben-David, a researcher at the Jerusalem Center for Public Affairs, says this latest crisis shows there's still a major threat.
LENNY BEN-DAVID: Israel made a great effort to go after the metro, as they called it, and it now appears that they failed to finish with the tunnels.
NORTHAM: Joel Roskin, a professor at Bar-Ilan University who focused on tunnels while in the Israeli military, says Hamas is continually building and adapting, making the tunnels deeper, zigzagging rather than straight lines.
JOEL ROSKIN: We know that Hamas is investing most of their resources also in intelligence, in mind and creativity in working on this tunnel complex. So we can expect that their tunnels are significantly more complex than what we saw in 2014.
NORTHAM: Kobi Michael, a Hamas specialist at the Institute for National Security Studies in Tel Aviv, says the militants have had help building the tunnels.
KOBI MICHAEL: Iran assisted Hamas with technological knowledge, military knowledge, weapon supply, money and engineering knowledge as well.
NORTHAM: But it's civilians who often pay the price in the tunnel war when Israel bombs tunnels but also destroys the buildings above them. Israel blames Hamas for tunneling under civilian buildings, but rights groups say that doesn't justify civilian casualties. And Bar-Ilan University's Roskin says there are other ways to destroy a tunnel.
ROSKIN: Using different types of liquids, gas, explosives. In 2019, in operations in Lebanon, the military tried to fill the tunnels with slurry, which is like a loose cement.
NORTHAM: In some cases, Israeli soldiers will have to enter the tunnel. An elite team called Samur - weasel in Hebrew - has been trained for tunnel combat. Reichman University's Richemond-Barak says soldiers will have limited communications underground and face booby traps.
RICHEMOND-BARAK: So we're looking at one-on-one combat, which is very different than what modern warfare really is about. This is a return to medieval ways of fighting.
NORTHAM: Major General Mickey Edelstein is commander of the Israel Defense Forces' operational planning team and led the military's tunnel warfare efforts in 2014.
MICKEY EDELSTEIN: And it is a challenge, but we have the right capabilities. I trust our forces.
NORTHAM: What could further complicate Israel's targeting the tunnels are the roughly 240 hostages being held by Hamas. Last month, an elderly hostage released by the militants said she had been led for hours through a spider web of tunnels and held with others for more than two weeks, far below the Earth's surface.
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