Hamas Has Reinvented Underground Warfare

When Hamas attacked Israel on October 7, it dragged Israel into one of the worst underground wars ever. By now, it is abundantly clear that the scale of Hamas’s subterranean complex is unprecedented and that the use of tunnels has contributed to casualties among civilians and soldiers. More consequentially, by sustaining underground operations over months, Hamas has delayed an Israeli victory, causing unimaginable diplomatic and political costs along the way.

In terms of tunnel warfare, the only war that compares is World War I, in which countless British and German soldiers died trying to expose, mine, and dig tunnels. No other use of tunnels in warfare comes close—neither the entrenchment of Osama bin Laden in the mountains of Afghanistan that enabled him to evade U.S. forces and plan attacks undetected; nor that of al Qaeda in the Islamic Maghreb in Mali, where tunnels were used in launching attacks from nearly impregnable underground hideouts; nor that of the Islamic State (also known as ISIS), which used tunnels to conduct attacks on U.S.-led multinational forces in Iraq and Syria. Hamas’s use of tunnels is so advanced that it more closely resembles how states use underground structures to protect command-and-control centers than what is typical for nonstate actors.

Hamas’s buildup of below-ground capabilities has shaken Israel’s assessment of subterranean threats. Israel never imagined becoming embroiled in an underground war of such proportions. If anything, Israel had been focused on eliminating the Hamas tunnels that cross into Israeli territory. The war in the Gaza Strip will likely spur the development of new doctrine and new methods to deal with this unique type of war. Hamas’s tunnel system has no doubt caught the attention of other militaries and nonstate actors, all of which are noting how effective they have been for Hamas’s survival in Gaza.

Now that Hamas has overcome most of the hurdles inherent in underground warfare—communication, navigation, low oxygen levels, and claustrophobia, among others—there is every reason to believe that the tactic will continue to spread. Hamas’s innovative use of the underground has redefined the strategic value of the surface, altered military encounters, and transformed the use of human shields.

OUT OF REACH

Surviving underground for long periods is no small feat, as the hundreds of Ukrainian fighters who lived in the tunnels beneath the Azovstal steel plant during a Russian onslaught on Mariupol in 2022 could report. Those forces quickly ran out of food and drinking water. They lacked the most basic sanitary and medical arrangements, not to mention Internet connection and the ability to maintain communication with the outside world. In Gaza, none of this has been an issue for Hamas. The people living and fighting in the Azovstal tunnels could not survive for more than two months underground, but Hamas has maintained a subterranean military presence for almost eight months. Hamas owes this record-breaking performance to a long maze of underground passageways spanning Gaza that includes fully outfitted kitchens, furnished command rooms, sophisticated data centers, tiled bathrooms, fenced detention cells, and designated work areas.

Hamas seems unfettered by geological constraints, engineering and planning difficulties, or the fear of survivability. The group has had plenty of time to sharpen its skills, experiment, and improve; decades of digging at the Egyptian border, inside Gaza, and into Israeli territory certainly helped. A tunnel exposed near the border crossing between Gaza and Israel, known as the Erez crossing, was almost ten feet wide and 164 feet deep. It was dug using civilian boring equipment, a first for Hamas.

Even the best digging skills, however, do not prepare fighters for prolonged stays underground. The conditions are harsh, oxygen is scarce, and communication with the outside world is limited. Hamas has shown that years of training and careful planning can help overcome these hurdles. Hamas’s tunnels include sleeping quarters, meeting rooms, and other underground structures, equipped with ventilation, electricity, toilets and washrooms, plumbing, and primitive yet effective communication networks. As the infrastructure improved, the downsides of living in and operating from the underground diminished. Massive stocks of fuel, food, and water inside the tunnels made it possible to live and conduct military operations underground. Extensive underground weapons-production facilities ensured that weapons supply and distribution would continue uninterrupted.

Israel underestimated the strategic ramifications of tunnel warfare.

Tunnel users everywhere are known to exit tunnels to restock, breathe fresh air, and communicate with the outside world, but Hamas leadership has barely been seen above ground. In April, reports surfaced that Hamas’s chief in Gaza, Yahya Sinwar, had visited his forces above ground, but only briefly. It is not clear how often Hamas fighters have exited the tunnels to resupply or recuperate. What is clear, however, is that Hamas has been able to direct military operations without interruption. Though it has suffered blows—particularly when Israeli strikes interrupt its communication systems—it has generally been able to ensure the continuation of the chain of command from its underground military base.

Hamas’s use of underground structures is more akin to how states, rather than nonstate actors, have traditionally used the underground. States rely on underground structures to house permanent and hard-to-reach bunkers capable of serving as command-and-control centers in times of crisis. These deeply buried facilities can host leaders, sustain weapons-production infrastructure, and ensure the continuation of the chain of command in an emergency. Canada, China, Iran, Israel, Russia, and the United States are known to possess these types of deeply buried facilities. They are larger, better equipped, more reinforced, and deeper than tunnels. Iran’s nuclear facilities are dug more than 300 feet into the ground (whereas most tunnels do not reach beyond 200 feet) and, as a result, are beyond the reach of even the most powerful weapons.

By contrast, terrorist groups have used tunnels mainly to shield themselves from surveillance technology and operate undetected. These rudimentary tunnels are used to hide and carry out surprise attacks. But in Gaza, many of the tunnels exposed by the Israel Defense Forces (IDF) resemble underground structures found in Iran and North Korea in terms of their size, depth, and method of construction. Their cemented arched ceiling has become a signature trait, with cement also used to build larger tunnel shafts. Compared with Hamas’s earlier tunnels, those dug in Egypt and Gaza in the late 1990s and even up to the 2010s, the engineering has significantly improved. Tunnels are now less prone to collapse, well lit, and much more livable.

Hamas has also increased its reliance on tunnels as part of its strategy, namely how it uses tunnels. It sees tunnel warfare as a long-term, strategic investment designed to ensure the survivability of its chain of command in war, not merely a tactic to counter Israel’s intelligence, surveillance, and reconnaissance capabilities. Militaries cannot fight tactical tunnels as they fight strategic subterranean threats. Bunker-buster bombs, for example, will not be sufficient to destroy such deeper and robust structures. A shift toward a more strategic use of tunnels reflects a focus on survivability rather than underground combat.

WAIT-A-MOLE

The tunnels have shaped the operations in Gaza in countless ways—compromising the likelihood of a swift Israeli victory, slowing down the pace of operations, making the rescue of hostages more difficult, placing civilians in harm’s way, and complicating the military and political environments for Israel. But one aspect is often overlooked, and it bears consequences for future wars: Hamas’s subterranean strategy has diminished the importance of the surface.

The Israeli journalist Ron Ben-Yishai has aptly described this new type of fighting as “a war carried out on two different levels.” In the initial stages of the war, the IDF sought to gain control of the surface to expose and eventually enter Hamas’s tunnels. But as its operation progressed, attention shifted to the passageways to and from the subsurface. The surface became just a conduit to reach underground tunnels and structures and ceased to be the focus of the fighting.

Enemy encounters and ground maneuvers changed as a result. Underground warfare is known to render the enemy invisible and out of reach. It is aptly and commonly described as a whack-a-mole game, in which the enemy pops out of the ground in an endless hide-and-seek competition. In Gaza, however, the enemy disappeared almost entirely, swallowed into its immense subterranean complex. Whack-a-mole became wait-a-mole. And since even waiting did not produce results, the Israeli military has had to use all sorts of subterfuges to extract Hamas fighters from underground.

This is not to say that Hamas fighters never emerge. They have fired deadly antitank missiles at Israeli troops and carried out other types of ambushes. But the way Hamas is operating shows that its use of tunnels has redefined not just the subterranean environment but also the value of and the nature of land combat. Encounters with the other side are less frequent, and like the tunnels themselves, they are difficult to detect. For example, booby traps near tunnel shafts indicate the presence of the enemy, but there is no enemy in sight, and when tunnels are finally penetrated, the enemy has moved to a different part of the tunnel network. The discovery of empty tunnels below the Al-Shifa hospital illustrates this vividly. In this environment, encounters do not occur naturally: they must be orchestrated.

If subterranean warfare has displaced land warfare in Gaza, it could happen elsewhere. Militaries must consider how to deal with the dwindling role of the surface when the enemy shifts from a tactical to a strategic use of the underground. The surface will continue to be relevant in war—at a minimum—in allowing access and control over underground structures and as the eventual location of most encounters. But these developments suggest that subterranean warfare might be best framed as a separate domain of war rather than as a mere subset of land warfare.

THE LIMITS OF TECHNOLOGY

Fighting in Gaza has also shown that advances in antitunnel technology have failed to deter groups such as Hamas from resorting to tunnel warfare. Israel arguably possesses the world’s most advanced antitunnel technology. Advanced detection and neutralization techniques were deployed to counter the threat of Hezbollah’s tunnels into Israel in 2018. Israel also trained special units in tunnel warfare, built subterranean training facilities, developed subterranean sensors to protect its borders, and mastered the difficult task of mapping tunnels by using drones. Between Operation Protective Edge in 2014, Israel’s last war in Gaza, and Hamas’s October 7 attack, the IDF significantly improved its capabilities in subterranean warfare, with a focus on training, equipment, and detection.

But Israel’s superior technology and advanced training did not discourage Hamas from investing significant time and human resources into building tunnels. At the same time, advances in technology led Israel to believe that it had quashed Hamas’s underground pursuits, even though the opposite was true. To put it in simple terms: as the technology improved, the digging intensified. Israel underestimated the strategic ramifications of tunnel warfare—a low-tech threat—when used on a grand scale and overestimated the ability of technology to counter it. It focused on the tactical aspects and on the cross-border tunnels, leaving Hamas free to develop subterranean capabilities of unprecedented proportions.

Making sense of this paradox is a key lesson from this war. Technology and military superiority cannot on their own stop the tunnel trend. Technology has failed both to deter subterranean threats and to counter them. Hamas is keenly aware that even the most sophisticated technology available will not be sufficient to counter such underground capabilities and therefore has deep confidence in the tactic. Hamas knew that its extensive tunnel network in Gaza would slow Israel’s response, diminish Israel’s competitive advantage, protect Hamas’s top leaders in Gaza, and inflict heavy civilian casualties. Low-tech warfare has paid off in Gaza, and it is a success that will boost tunnel warfare everywhere.

HUMAN SHIELDS 2.0

Hamas’s use of Israelis and foreign civilians as human shields is a significant and concerning innovation of the ongoing Gaza war. As is well known, Hamas took hundreds of hostages as part of its massive October 7 attack on Israel, many of whom are still being held in Gaza. These people are commonly referred to as hostages, but the reality is more complex than the word “hostage” suggests.

Hamas has innovated, first, by bringing innocent civilians inside the tunnels as human shields and, second, by using civilians from Israel and other countries, rather than Palestinian civilians, as human shields. In contemporary warfare, human shielding refers to the act of placing civilians—typically one’s own civilians—in and around military targets with the aim of immunizing such targets from attack. The tactic, which is prohibited under international law, has sadly flourished in the context of urban warfare. Many terrorist groups, including Hamas in general and in the context of underground warfare in particular, have found it beneficial to hide behind their civilian population: Western militaries call off strikes when the harm expected to be caused to civilians becomes excessive to the military advantage anticipated from the strike. Placing civilians inside tunnels has had the intended effect of complicating rescue efforts, constraining military operations, and immunizing key military assets of Hamas. This use of hostages is a return to a classic yet prohibited tactic of war of using prisoners of war for force protection. During the American Civil War, both sides used prisoners as human shields, and the Germans used British prisoners of war as human shields during World War II.

The civilians taken captive and held incommunicado by Hamas are both hostages and human shields. This innovation in hostage-taking has enabled Hamas to maximize political and military aims far beyond its declared objective of obtaining the release of Palestinian prisoners from Israeli jails. The taking of hostages has torn Israeli society apart and has led to the Israeli government conditioning victory on unattainable and irreconcilable objectives. It has given Hamas power at the negotiating table and caused Israel’s allies to request concessions in return for the release of the hostages. It has also facilitated Hamas’s ruthless psychological war. Militaries must take note of these innovative uses of the underground, which can bring states to the brink of operational and political paralysis, so that they can anticipate how underground tactics might be used in future wars by their adversaries.