The use of tunnels in wars is not new. Seeking advantages by using either natural or man-made spaces underground is as ancient as warfare itself—from stories of tunnels being used to win massive battles in the bible to underground spaces becoming key factors to urban battles, like Mariupol and Bakhmut, in the ongoing war in Ukraine. Modern nations including the United States, China, and North Korea invest billions in deep-buried military bunkers and tunnel complexes. But what Israel has faced in Gaza represents a unique first in war—namely, a case in which tunnels form one of two pillars, along with time, of a combatant’s political-military strategy.

Before the Israel-Hamas war, both the presence of Hamas tunnel networks and their growth over the years were very well known. The network was referred to as Gaza’s “Metro” or “lower Gaza.” The Israel Defense Forces (IDF) and scholars estimated before the war that there were three hundred miles of tunnels ranging from fifteen feet to over two hundred feet below the surface. The estimates were wrong.

After three months of close combat and discovering over 1,500 tunnel shafts and underground passages, the IDF has learned enough to require the estimates to be revised. Israeli forces have unearthed massive invasion tunnels two and a half miles long, underground manufacturing plants, luxury tunnels with painted walls, tile floors, ceiling fans, and air conditioning, and a complex, layered, labyrinth underneath all areas of Gaza. The new estimates say the network may include between 350 and 450 miles of tunnels, with close to 5,700 separate shafts descending into hell.

New estimates also indicate the construction of this subterranean network could have cost Hamas as much as a billion dollars. The group has poured resources over fifteen years not just into constructing tunnel passages, but for blast doors, workshops, sleeping quarters, toilets, kitchens, and all the ventilation, electricity, and phone lines to support what amount to underground cities. As much as 6,000 tons of concrete and 1,800 tons of metals have been used in this subterranean construction.

The sheer size of Hamas’s underground networks may, once fully discovered, be beyond anything a modern military has ever faced. One of the last conflicts that involved a large amount of tunnel complexes was the Vietnam War. American forces and others faced some tunnel complexes that ranged up to forty miles in length and one of the most concentrated places of tunnels, near Saigon at Cu Chi, contained 130 miles of passageways.

There are larger military tunnel complexes in the world. China is believed to have three thousand miles of tunnels and bunkers capable of withstanding nuclear attacks in a network that has been called the “Underground Great Wall.” Some estimates show North Korea has over five thousand tunnels and infrastructure that includes multiple underground air bases with runways, radar sites, and submarine ports inside mountains.

But more importantly than the scale of the tunnels in Gaza, the Israel-Hamas war is the first war in which a combatant has made its vast underground network a defining centerpiece of its overall political-military strategy.

In the past, and even in most cases today, military tunnels and bunkers have been built specifically to gain a military advantage. They are used for smuggling, kidnapping, and invading or defending territory. Underground spaces enable militaries to conserve capabilities by avoiding detection and strike, to hold terrain by using the tunnels for mobile defense tactics, or even offensively to use guerrilla tactics to attrit the attacking force.

For the first time in the history of tunnel warfare, however, Hamas has built a tunnel network to gain not just a military advantage, but a political advantage, as well. Its underground world serves all of the military functions described above, but also an entirely different one. Hamas weaved its vast tunnel networks into the society on the surface. Destroying the tunnels is virtually impossible without adversely impacting the population living in Gaza. Consequently, they put the modern laws of war at the center of the conflict’s conduct. These laws restrict the use of military force and methods or tactics that a military can use against protected populations and sites such as hospitals, churches, schools, and United Nations facilities.

Almost all of Hamas’s tunnels are built into civilian and protected sites in densely populated urban areas. Much of the infrastructure providing access to the tunnels is in protected sites. This complicates discriminating between military targets and civilian locations—if not rendering it entirely impossible—because Hamas does not have military sites separate from civilian sites.

Hamas’s strategy is also not to hold terrain or defeat an attacking force. Its strategy is about time. It is about creating time for international pressure on Israel to stop its military operation to mount.

Hamas is globally known for using human shields, which is the practice of using civilians to restrict the attacker in a military operation. The group wants as many civilians as possible to be harmed by Israeli military action—as one of its officials put it, “We are proud to sacrifice martyrs.” It wants the world’s attention on the question of whether the IDF campaign is violating the laws of war in attacking Hamas tunnels that are tightly connected to civilian and protected sites. It wants to buy as much time as is needed to cause the international community to stop Israel. Its entire strategy is built on tunnels.

The tactical challenges Hamas tunnels present to Israel are thereby compounded by strategic challenges. To deal with tunnels at the tactical level, Israel has demonstrated some of the world’s most advanced units, methods, and capabilities to find, exploit, and destroy tunnels. From specialized engineer capabilities and canine units to the use of robots, flooding to clear tunnels, and both aerial-delivered and ground-emplaced explosives, to include liquid explosives, to destroy them. Arguably, no military in the world is as well prepared for subterranean tactical challenges as the IDF. But the strategic challenge is entirely different. To destroy many of the deep-buried tunnels, the IDF has required bunker-busting bombs, which Israel is criticized for using. And most importantly it has required time to find and destroy the tunnels in a conflict in which Hamas’s strategy is aimed at limiting the time available to Israel to conduct its campaign.

Hamas’s strategy, then, is founded on tunnels and time. This war, more so than any other, is about the underground and not the surface. It is time based rather than terrain or enemy based. Hamas is in the tunnels. Its leaders and weapons are in the tunnels. The Israeli hostages are in the tunnels. And Hamas’s strategy is founded on its conviction that, for Israel, the critical resource of time will run out in the tunnels.

John Spencer is chair of urban warfare studies at the Modern War Institute, codirector of MWI’s Urban Warfare Project, and host of the Urban Warfare Project Podcast. He is also a founding member of the International Working Group on Subterranean Warfare. He served twenty-five years as an infantry soldier, which included two combat tours in Iraq. He is the author of the book Connected Soldiers: Life, Leadership, and Social Connection in Modern War and coauthor of Understanding Urban Warfare.

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: Israel Defense Forces (adapted by MWI)