By Eric Vandenbroeck and co-workers

The No Blueprint Assault

No blueprint exists for the ground assault that Israel has launched in the Gaza Strip. Israel must balance its stated objective of eliminating Hamas’s subterranean military capabilities with the need to protect its troops in a highly volatile environment, and it must do so while minimizing harm to the innocent population of Gaza and to Israeli nationals and others who have been taken, hostage. For these reasons, Israel’s ground assault is guaranteed to be a slow and difficult operation.

Working in Israel’s favor is the overwhelming size and capability of its military. After Hamas’s October 7 attack, the Israeli military heavily bombed Gaza for three weeks before sending in ground forces. Today, Israeli airstrikes continue to degrade Hamas’s capabilities and infrastructure. Israel has tanks, an air force, and the most advanced weapons systems in the world, plus the support of the United States. But Hamas has been able to reduce this battlefield asymmetry through its concealment within the civilian population and its underground tunnel network.

For Israel to maintain its strategic advantage, it will need to avoid subterranean combat as much as possible. Although attention has turned to Israel’s ground invasion of Gaza, the elimination of Hamas’s tunnel network is more a job for Israel’s air force than for its ground troops, whose tasks should be to solidify the results of the extensive yet focused aerial campaign, to verify that subterranean structures have effectively been eliminated, to destroy any remaining ones, to collect useful intelligence, and to kill any Hamas leaders who survive airstrikes.

If military history is any indication, the way to achieving these goals will sadly be long and bloody. The destruction of Hamas’s high-value military assets, hidden beneath the surface, will cause casualties among innocent civilians who remain in the zone of combat. Evacuation orders are meant to minimize civilian casualties; so are precision-guided strikes, leaflets, and text messages. The attempt to mitigate civilian casualties also led to a slower pace of the war. Military commanders and their legal advisers will have to make complicated assessments, required under the law of war, to determine whether the expected collateral damage to civilian life and civilian infrastructure “would be excessive about the concrete and direct military advantage anticipated” from the strike. But when it comes down to it, the harsh reality of this combined urban and subterranean warfare means that civilians will get hurt, as was the case when the U.S. and partner forces fought the Islamic State (ISIS) in Mosul, Iraq, and Raqqa, Syria. There are no magical solutions to overcome the unique operational difficulties inherent to this terrain, as tragic as it sounds. Israel’s actions will unavoidably pose a great risk to its forces, to innocent Palestinians in Gaza, and the hostages.

Despite the difficulty of managing these risks, the destruction of Hamas’s network of tunnels and subterranean structures must remain a top priority for the Israeli military as this operation evolves. Leaders and fighters can be replaced, but Hamas will be hard-pressed to recover and reorganize while being exposed and unable to hide.

 

Going Underground

Israel faces the almost insurmountable operational challenge of identifying and eliminating subterranean military capabilities in a tunnel-laden urban battlefield that Hamas has had years to prepare. Distributed within this urban and subterranean jungle are the over 200 people Hamas is holding hostage in Gaza. Their presence makes Israel’s options even more limited. Israel perceives the kidnapping of any number of soldiers and civilians as a strategic event. Hamas has taken hostage children, babies, women, and elderly people, as well as an unknown number of soldiers. Until the release of all hostages, anti-tunnel operations in Gaza—via deep-penetrating airstrikes or a ground incursion—put their lives at risk and add another layer of complexity to Israel’s military operation. In this setting, the traditional dilemmas associated with urban warfare, chief among them the need to minimize the harm caused to innocent civilians, are magnified exponentially.

Hamas has purposely placed its entire military apparatus within and underneath civilian infrastructure, from supply lines and transportation routes in tunnels crisscrossing Gaza’s cities to underground command-and-control centers, ammunition depots, living quarters, rocket launchers, and even military hospitals. Hamas’s main military bases are located beneath Gaza’s hospitals and schools, notably Al Shifa Hospital in the heart of Gaza City, and beneath many facilities operated by the United Nations. By using civilians, hospitals, and schools to shield itself from attack, Hamas has committed war crimes, certainly; but it has also made it that much more difficult for Israel to achieve substantial military gains.

Israel’s perception of how to deal with this threat has changed radically over the years. Israel assumed that Hamas’s digging would stop after Israelis withdrew from Gaza in 2005. That assumption proved wrong: Hamas has only increased its reliance on tunnels over the past two decades. When Hamas kidnapped Israeli soldier Gilad Shalit in 2006 via one of its tunnels between Gaza and Egypt, Israel blamed it on improper military preparation rather than on a flawed assessment of the threat posed by the tunnels. Israel saw the tunnels as simply another method used by terrorists to launch attacks, not as the strategic threat that they were quickly becoming.

That perception changed with the 2014 Gaza war, also known as Operation Protective Edge, in which Israel launched an air campaign followed by a two-week ground operation inside Gaza. Once inside Gaza, the Israeli military was surprised by the extent of Hamas’s subterranean operations, and it focused on destroying Hamas’s cross-border tunnels. Now, following Hamas’s October 7 attack, during which the group killed more than 1,400 people inside Israel, it has become clear that degrading Hamas’s capabilities requires the destruction of the entire subterranean network, or more realistically, a significant portion of it.

The challenge for the Israeli military will be doing this while avoiding fighting inside Hamas’s warren of unmapped, dark, and claustrophobic tunnels. In this terrain, Hamas has the upper hand. It has perfected the art of maneuvering, communicating, and surviving below the surface. The underground tunnels neutralize Israel’s military capabilities and serve as a great equalizer between the two sides. Aircraft, tanks, mechanized vehicles, and modern communications either cannot operate or are made irrelevant underground. The three-dimensional battlefield becomes an environment in which any sophisticated military would struggle to prevail.

On the face of it, this is a conflict that appears to be completely asymmetric between a state and a terrorist group, but subterranean warfare reduces this imbalance, making underground warfare attractive to terrorist groups all over. As advanced surveillance capabilities, signals intelligence, and unmanned vehicles have proliferated on the battlefield, the underground has become increasingly attractive to groups such as al Qaeda, ISIS, and Hamas.

Even the most sophisticated armies—especially the most sophisticated armies—find tunnels unsettling. The presence of tunnels elicits deep fears of the unknown and affects all aspects of a military operation, from the ability to secure territory to intelligence gathering and rescue operations. Tunnel combat negates the basic military doctrine of modern armies, which have invested in technology to overcome less sophisticated enemies and to compete on a level playing field in peer-to-peer warfare.

The harm inflicted on U.S. forces during the Battle of Iwo Jima at the end of World War II serves as a reminder of how deadly subterranean warfare can be. When they landed on the island, U.S. forces were met by thousands of Japanese soldiers who had entrenched in a large tunnel complex equipped with fortified rooms, steel doors, and military medical facilities. The battle, which killed an estimated 7,000 American troops over several weeks, demonstrated the scope and nature of the violence that underground warfare can generate. Those tunnels, unlike Gaza’s, were in mountainous terrain, far from the civilian population. But what Iwo Jima and Gaza both demonstrate is the difficulty of destroying the entirety of a large and intricate network of military tunnels. When Israeli Prime Minister Benjamin Netanyahu announced the destruction of 32 tunnels, including 14 cross-border tunnels, in 2014, plus another 62 miles’ worth of tunnels in 2021, it was clear that only a small portion of Hamas’s immense subterranean network had been hit. This was a setback that Hamas has since overcome.

 

The Hidden Problem

The destruction of Hamas’s underground infrastructure in Gaza will remain a central objective for the Israeli military, regardless of the cost and the operational difficulties. It will be important for Israel to eliminate, rather than neutralize, Hamas’s tunnels. Neutralization, by pouring cement into the tunnels or by sealing their openings, cannot permanently remove the security threat. It is time-consuming but not impossible to pierce through cement. Only a “hard kill,” meaning the collapse of the walls and roofs of the subterranean structures, will sufficiently degrade Hamas’s capabilities over the long term.

Bulldozers can be used to expose tunnels during a ground operation. Drones, robots, or dogs can help clear tunnels. There might be a need to enter the tunnels to rescue hostages, as a measure of last resort. But a ground operation will not bring about the destruction of Hamas’s underground military apparatus. This is a job done mainly from the air, using thermobaric weapons, bunker buster bombs, and precision-guided munitions, and from the surface using liquid emulsion (a combination of two harmless liquids that turn into a powerful explosive when mixed) and other and newer tools developed by the Israeli military. This is how most states have eliminated subterranean threats in the past, and this is what Israel should do, as well.

Destroying Hamas’s tunnel network is the most difficult aspect of the Israeli military’s mission today, but it is also among its most important. It is at least as important as the elimination of Hamas’s chain of command. The destruction of the tunnels will leave Hamas with a compromised infrastructure and a depleted arsenal, resources more difficult to replace than fighters.

 

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