Daphné Richemond-Barak
In the 10 weeks since Israel launched its ground campaign against Hamas in the Gaza Strip, its troops have detected and mapped the path of a series of underground tunnels—part of a vast network built by Hamas over nearly two decades.
The network—which Hamas fighters use to hide themselves and their captives, plan operations, store weapons, and ambush Israeli soldiers—is a crucial part of the group’s military infrastructure. It has proven to be Israel’s greatest vulnerability in the war. Destroying it is essential to degrading Hamas’s military capabilities and preventing attacks similar to the one that the group carried out on Oct. 7, killing about 1,200 people. Yet the process has been painstakingly slow and cumbersome.
As the new year begins, a question now looms large for military planners and for analysts seeking to draw lessons from this campaign: How close is Israel to destroying the tunnel network? And how much longer will it take for its troops to prevail over this threat?
Tunnel warfare has always been one of the deadliest and most complicated forms of combat. During World War I, many thousands of British troops died seeking to destroy German underground positions. Years later, the U.S. struggled to defeat deeply entrenched enemies in Vietnam, Afghanistan, and Iraq.
Armies faced with these subterranean threats have typically deployed their most powerful weapons, including B-52s, flamethrowers, thermobaric weapons, bunker-buster bombs, and other aerial precision-guided missiles. Often, these measures have fallen short of eliminating an enemy operating from caves, tunnels, and other artificial or human-made subterranean structures.
Israel has learned this the hard way. The discovery in 2014 of cross-border tunnels dug by Hamas between the Gaza Strip and Israel brought home the significant security risk that they pose, particularly when they come near the civilian population.
Israel’s military operation against Hamas that year was the first war in the 21st century in which tunnels became the focal point of military operations—a development that would later shape the Syrian civil war. It left Israel keenly aware that tunnels could be used to kidnap soldiers and civilians, infiltrate Israeli territory, and carry out brutal attacks. But the Israeli focus on tunnels, if there was a concerted one at the time, was largely devoted to cross-border tunnels—and less so on Hamas’s ever-growing subterranean military buildup inside the Gaza Strip.
After the 2014 war, Israel shifted to a more strategic approach and ramped up its efforts. It created elite units specialized in tunnel warfare, built its own tunnel structures for training soldiers, improved tunnel detection with mobile units and targeted research and development, came up with unique tactical solutions to enhance preparedness, and boosted cooperation with partners and allies.
As a result, the Israel Defense Forces (IDF) went into the current war possessing the most advanced military capabilities in the detection, mapping, neutralization, and destruction of tunnels. And yet, this neither deterred Hamas from digging nor lessened the challenge of fighting in a subterranean environment. Even the most specialized units of the IDF have suffered losses because of booby trapped tunnel entrances.
These units have also uncovered a new generation of Hamas tunnels. The group’s rudimentary structures of the early 2000s were reinforced with wood planks. The current networks are deeper and more hardened, resembling the large infiltration tunnels of North Korea. Hamas used advanced civilian boring technologies to dig them, taking its subterranean capabilities to the next level.
Hamas’s growing reliance on the tunnels and its elaborate construction effort have paid off. Never in the history of tunnel warfare has a defender been able to spend months in such confined spaces. The digging itself, the innovative ways Hamas has made use of the tunnels, and the group’s survival underground for this long have been unprecedented.
For Israeli soldiers, advancing in this dangerous terrain has required a systematic approach. The IDF’s aerial campaign and early ground operation sought to gain control of the surface and reduce the risks that urban warfare poses to combatants and civilians. Buildings were destroyed to limit sniper attacks and ambushes, and northern Gaza was largely evacuated to reduce civilian casualties. Troops proceeded to clear the ground with armored bulldozers to expose tunnel openings.
These openings, known as tunnel pits, are essentially deadly holes in the ground. They can vary in size and shape and are usually camouflaged and booby-trapped. They lead down to tunnel shafts—the part of the subterranean structure used to penetrate deep into the ground and access the broader network of tunnels.
During their sweep, Israeli soldiers uncovered hundreds of tunnel pits, making the advance slow and complicated. These pits enabled Hamas fighters to pop out of the ground, fire automatic weapons or rocket launchers at the forces, and disappear within seconds. The IDF sealed or destroyed many of these openings as a temporary measure, so that forces could continue their advance and secure the grounds.
The next step was to map and learn more about the tunnel network. Soldiers remained at the surface until they could safely enter tunnels to gather intelligence and search for hostages—some 240 of which were taken during Hamas’s Oct. 7 attack on Israel.
The troops first sent in robots and drones equipped with video cameras into the tunnels, and dogs that could detect the presence of explosives or people. These and other measures helped expose the scale and scope of the network and allowed the entry of the soldiers into the tunnels—before moving to the destruction phase. Skipping any of these steps would have been fatal for IDF soldiers, Israeli hostages, and Palestinian civilians.
Time is the most precious resource in the endeavor, as the troops operate in a complex military environment that combines urban warfare, tunnel warfare, and search-and-rescue operations. Locating the rest of the tunnels, working around booby traps, and avoiding surprise attacks all require a slow and methodical approach. In Gaza, as in previous underground wars, the tunnels have unsettled the forces, caused significant casualties, delayed the end of the war, and made victory less certain.
Already, it has become clear that Israel cannot possibly detect or map the entirety of Hamas’s tunnel network. For Israel to persuasively declare victory, in my view, it must destroy at least two-thirds of Hamas’s known underground infrastructure.
To get there, Israel has reportedly decided to pump large volumes of seawater into the tunnels. Tunnel warfare has traditionally spawned military innovation, and this war is no exception. At the strategic level, seawater flooding is an attempt by the IDF to gain some military advantage in a terrain that the enemy has exploited, undeterred, for decades. At the operational level, the flooding could represent an expansion of the anti-tunnel arsenal, which to date consisted almost exclusively of bunker-buster bombs. These bombs have a limited capacity to penetrate the ground and cannot be used in all terrains.
This wouldn’t be the first time that armies have flooded enemy tunnels during a war. But doing so in the traditional method, via tunnel pits, has only limited impact. To succeed in destroying the structure and producing what’s known in the trade as a “hard kill,” water must be injected directly from the sea into the horizontal sections of the tunnels at high volume and pressure—enhancing the force exerted on the cement. Only an approach that includes these three elements—high volume, high pressure, and direct horizontal injection—can bring about the complete destruction of the tunnel structure.
There is some fear that the horizontal pumping of seawater into the tunnels could, incidentally if not intentionally, contaminate groundwater sources. The coastal aquifer, the only source of water accessible to Palestinians in Gaza, is already known to be polluted and unfit for consumption due to over-abstraction. The possibility of causing irreversible damage to the aquifer would have to be compared to the potential damage inflicted to civilian life aboveground by other methods of tunnel destruction—including aerial bombing.
The seawater method might not be deployed in all situations. Some of the tunnels are too far from shoreline, while others are deliberately disconnected from the main clusters. In tunnels where hostages are thought to be held, Israel might refrain from using this method altogether. Still, this approach makes it possible, at least in theory, for Israel to achieve its goal of destroying substantial parts of the tunnel infrastructure.
As Israel moves to destroy the underground network, troops remain under fire, and additional tunnels are discovered each day. Completing this job could take a few more months. In a tunnel war requiring stamina, time, and perseverance, ending the war prematurely could mean defeat. To avoid such an outcome, Israel’s ability to determine its own timetable is key.
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