Before the war against Hamas in Gaza, the Israel Defense Forces were one of the most prepared militaries in the world for underground warfare. The IDF were the only army to have a full brigade-sized unit dedicated to training, manning, equipping, researching, developing new technologies and tactics, learning, and adapting solely for underground warfare. Still, the challenges they faced early in their campaign in Gaza, many of which they struggled initially to overcome, speaks to the incredible complexity of subterranean warfare. Their responses to these challenges signal a paradigm shift in modern approaches to underground warfare.
The Long List of Underground Challenges
One of the main reasons the IDF were unprepared for Gaza’s underground spaces was simply that no military had faced anything like it in the past—not even Israeli ground forces. The IDF faced a Hamas military organization that had spent over fifteen years engineering the infrastructure of an entire region—to include over twenty major cities—for war, with the group’s political-military strategy resting on a vast and expensively constructed subterranean network under Gaza’s population centers.
The Hamas underground network, often called the “Gaza metro,” includes between 350 and 450 miles of tunnels and bunkers at depths ranging from just beneath apartment complexes, mosques, schools, hospitals, and other civilian structures to over two hundred feet underground. There are estimates of over five thousand separate shafts leading down into Hamas subsurface spaces. In past wars, where underground environments were used, the tunnel networks were subordinate to the surface and were not built solely under population centers mostly to be used as massive human shields.
IDF investigations and captured Hamas documents produced reports that it took Hamas a year to dig one kilometer of standard tunnel at a per-kilometer cost of $275,000. A number of factors—size, type, and function, for examples—can raise the costs well beyond that of a standard mobility tunnel.
The variety of tunnels in Gaza makes it difficult to estimate the underground network’s overall cost, but Hamas reportedly spent $90 million to build just three dozen tunnels in 2014, and some analysts place the network’s total cost at over $1 billion.
On October 7, 2023, the IDF had a brigade of special operations forces engineers, the Yahalom unit, fully equipped with technologies and tactics to accomplish the full range of underground warfare tasks, from detecting, securing, and mapping tunnels and bunkers to exploiting, clearing, neutralizing, and destroying them. This unit has spent decades researching, developing, testing, and purchasing technologies to overcome the challenge of military operations underground. This work includes a decade-long antitunnel cooperation and exchange program between Israel and the United States to jointly develop technologies and tactics that address the challenges of underground warfare. The IDF also has a robust military working dog program, the Oketz unit, that includes dogs trained for operating in subterranean spaces.
IDF units like Yahalom had plenty of work to do to prepare for underground warfare. Soldiers need special equipment to breathe, see, communicate, navigate, breach obstacles, and even shoot underground. Almost every piece of their standard military equipment designed for the surface will not work once they enter the subsurface. Line-of-sight and satellite-enabled technologies—including navigation, communication, and drones—are rendered useless. Night-vision goggles that rely solely on ambient light will not work in an environment where there is none. A blast from a weapon or explosive detonated in enclosed underground spaces can cause harmful pressures and blast injuries making it dangerous to even fire a personal weapon if the soldier is not wearing the proper protective gear.
The Culture Component
A unique challenge that all militaries face in dealing with underground warfare is one of culture. Any military force’s culture is guided by its history, priorities, and warfighting concepts. Whether that culture acknowledges and prepares for the underground challenges described above is determined by an institutional belief about whether or not underground spaces will be prominent features in future warfare. For example, the US Army’s cultural views surrounding tunnels and subterranean spaces is that they are obstacles to be dealt with when encountered. The service’s doctrine recommends that US soldiers “should avoid entering and operating in subterranean environments when possible.” If entering cannot be avoided, the doctrine describes the primary tasks as clearing and securing the subterranean environment.
The IDF have their own long history of dealing with tunnels, especially cross-border tunnels. Hamas and Hezbollah have used cross-border tunnels in the past to conduct surprise attacks on IDF outposts or small patrols in a bid to kidnap Israeli soldiers. This led to the IDF to develop advanced detection, mapping, and navigating capabilities, as well as—in an emergency such as a soldier being taken back into a tunnel—the tactics to follow an enemy underground.
The IDF also developed advanced tunnel-striking capabilities with a wide variety of bunker-busting munitions. In the 2021 Operation Guardian of the Walls, the IDF believed they had destroyed sixty miles of Hamas tunnels in Gaza. Captured documents show that after this 2021 operation, the Hamas leadership authorized $225,000 to install more blast doors in tunnel segments to protect against IDF bunker-busting munitions collapsing more of the tunnel beyond the point where the bomb directly strikes. Hamas also increased production of handbooks showing their fighters how to survive and fight in tunnels.
In general, the IDF culture before 2023 was marked by the belief that tunnels should be dealt with by specially trained forces and that regular troops should only be sent underground as a last resort.
Adapting to Tunnels
At the beginning of the IDF operations against Hamas in Gaza after the October 7 attack, the IDF targeted many bunkers and tunnels with precision-guided bunker-busting munitions. These strikes were based on intelligence regarding the locations of tunnels, their purpose and value to the enemy, their contents, considerations about the presence of hostages or civilians, and other factors.
Once the ground campaign began, the IDF knew they would be encountering a lot of tunnels.
They task-organized squad-sized elements of Yahalom to as many maneuvering units as possible. The force that entered Gaza rapidly learned how to identify visual indicators of tunnel shafts, such as markings on buildings, the presence of infrastructure needed in the tunnels for power or ventilation, and other identifying features.
Once a shaft was located, it was generally secured and then Yahalom was called forward to investigate it. Even identifying a shaft was dangerous and time-consuming. The IDF lost five soldiers in early November 2023 from a booby-trapped tunnel entrance. Hamas’s use of booby traps outside and inside their tunnels was pervasive. In some cases, Hamas tunnels were built with improvised explosive devices embedded into the walls. This allowed Hamas fighters to arm and then leave their booby-trapped tunnels quickly.
If a shaft was determined to be a tunnel it was carefully interrogated, mapped, and searched. Many advanced technologies were used in this process, including drones and robotic devices designed to work underground. In some cases, military working dogs with cameras mounted on their backs were deployed, but the risk of losing dogs to booby traps made this tactic rare. During this time, Israel continued to be reluctant to send troops underground and only did so after tunnels were searched for potential dangers.
In fighting Hamas defenders, the IDF immediately faced enemy brigades, battalions, and companies that each had tunnel networks supporting their operations. In northern Gaza, the IDF had weeklong battles over single neighborhoods because of Hamas’s ability to pop in and out these networks and avoid decisive engagement.
In one attempt to combat Hamas’s use of their tunnels, the IDF procured and deployed what is to reported to be at least five industrial pumps to push thousands of cubic meters of water per hour into the tunnels to literally flush Hamas fighters out of them. The flooding had minimal impact. In one case, as one IDF officer I spoke to during a research visit told me, it took two weeks for a small Hamas tunnel to fill before the IDF finally saw Hamas fighters on the surface where they could be targeted.
Due to the tunnels’ porous concrete lining, the water simply drained out of them. Some tunnels were even built with drainage holes in them, while in others blast doors complicated the process. Flooding had little impact and was too time-consuming to use as a primary method to force Hamas fighters out of their tunnels. And ultimately, flooding would not destroy a tunnel.
The more the IDF engaged with the Hamas tunnel network, the more they adapted. Stopping for every suspected tunnel shaft and waiting for Yahalom to investigate severely slowed the momentum of maneuvering forces. Many of the suspected shafts were simply wells, civilian infrastructure, or other types of tunnels. The IDF quickly realized they had to push some of the specialized knowledge of Yahalom lower and to general-purpose soldiers. The regular IDF soldiers began to become proficient at dealing at least with shaft identification, site securing, and initial investigations.
The IDF began to realize that in many areas, the tunnels were a system of systems. Each Hamas company, battalion, and brigade had its own networks of tunnels that factored into how they would fight and move around. Some of these networks connected to each other while others were separate.
Once the IDF were able to focus intelligence efforts on determining the classification and architecture of a tunnel system in a specific area or neighborhood, their success in finding and dealing with tunnels significantly increased.
The IDF also developed a typology of Hamas tunnels. Some Hamas tunnels were tactical, such as small-unit tunnels that ran from building to building giving Hamas fighters the ability to hold specific terrain. Some were more operational as they connected different battalions or brigades to each other or provided operational mobility—like the mile-long tunnels running underneath the river basin of central Gaza to connect the region’s northern and southern portions. What to do about a specific tunnel and the urgency of action could be determined by proper identification of the type of tunnel that had been encountered.
Despite the IDF adaptations, a challenge remained: that of Hamas forces using the tunnels for their defensive operations as long as they could and then simply lining the tunnels with booby traps as they fell back to different tunnels. The tunnels gave Hamas the ability to control the initiative of most battles in Gaza.
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The views expressed are those of the author and do not reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.
Image credit: IDF Spokesperson’s Unit
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