“Those who go beneath the surface do so at their peril.”
So warned Oscar Wilde in The Picture of Dorian Gray. Of course, his words of caution were aimed at consumers of art and not at twenty-first-century military forces. And yet for those forces, the peril beneath the surface is even more real. Even a military with extraordinary capabilities above the ground will quickly encounter extreme limitations to those capabilities below it.
So when the Israel Defense Forces acknowledged having been quietly carrying out raids into Hezbollah tunnels in southern Lebanon for months, the natural question for many observers was why. Examining that question highlights lessons on underground warfare, illuminates how Israel likely intends to treat Hezbollah’s tunnels in its plans for a broader campaign against the group, and offers a glimpse into the capabilities required to overcome the subterranean hazards of the modern battlefield.
Hezbollah’s Tunnels
Much is unknown about Hezbollah tunnels. Like the Hamas tunnels in Gaza that Israeli forces have contended with during their military campaign there, the only way to know for sure how many tunnels there are—and their scale, form, and purposes—is discovering them on the ground.
Still, there are some publicly known details about Hezbollah’s tunnel network. Some experts believe the group started digging tunnels in southern Lebanon as early the mid-1980s, when Israel withdrew from most of the Lebanese territory it had occupied since its 1982 invasion to a limited strip along the southern border with Israel. When Israeli forces later withdrew fully, in 2000, Hezbollah continued to dig. Its fighters used tunnels extensively during the 2006 Second Lebanon War. According to a RAND report, Hezbollah’s bunkers were “40 meters underground, covering an area of two square kilometers, that included firing positions, operations centers, connecting tunnels, medical facilities, weapons and ammunition stockpiles, ventilation and air conditioning, bathrooms with hot and cold running water, and dormitories, all with a roof built of slabs of reinforced concrete almost three feet thick.”
In late 2018, Israel initiated Operation Northern Shield to find and destroy Hezbollah cross-border tunnels. Israel found six such major attack tunnels intended to allow thousands of Hezbollah fighters to flow into Israel during some type of invasion.
Today, analysts believe Hezbollah has used the years since 1980, and especially since the 2006 war, with the aid of state actors like North Korea and Iran, to build hundreds of kilometers of tunnels. This network includes single contiguous tunnels as long as forty-five kilometers and some tunnels connecting to Hezbollah’s stronghold in the Beqaa Valley, near the Syrian border, and to Beirut. Hezbollah tunnels, like those of Hamas, range from just below the surface underneath buildings to over a hundred meters deep.
It is important to note there are major differences between Hamas and Hezbollah tunnels. While some of the functions may be the same, the geology, construction, location, scale, and primary purposes are completely different.
Southern Lebanon consists of hilly, rocky terrain, requiring Hezbollah to dig with drills into solid rock over months and years to create single tunnels. In Gaza, by contrast, sandy sediment allows for digging with simple hand tools, making tunnels quicker to dig but also requiring large amounts of concrete to reinforce them. Hezbollah’s rocky tunnel construction also makes them extremely sturdy, which affects which bunker-busting munitions can reach the tunnels. In addition to running under civilian areas and wooded ground, many of Hezbollah’s tunnels and bunkers are inside mountains. The geographic scale and the variety of terrain pose a different challenge than the network of Hamas tunnels under flat and very dense urban terrain.
While Hezbollah uses human shields by building tunnels under civilian homes, unlike Hamas tunnels, the Hezbollah tunnels are not almost exclusively under civilian urban areas or used as the center of gravity by attempting to cause the maximum civilian deaths on the surface to achieve their political goal in wars.
Why Go Underground?
But why has Hezbollah spent decades digging? What military purposes do the tunnels serve?
Like tunnels throughout the history of warfare, Hezbollah’s subterranean spaces offer its fighters a number of advantages. Buried deep within rocky ground, Hezbollah fighters and leaders are more protected than anywhere else in southern Lebanon from Israel’s aerial supremacy and the strike capability of its precision-guided munitions. The tunnels also enable concealed movement and maneuver—some are wide enough for convoys of vehicles and allow even large weapon systems to be repositioned where they can be most effectively employed. Tunnels offer safe places to store supplies and cache weapons and ammunition. Command-and-control facilities placed underground offer a secure means for Hezbollah commanders to employ their forces. Even barracks can be placed underground. So the years of digging tunnels, expanding them and connecting them, make it possible today for Hezbollah to benefit both logistically and from a protection standpoint. But as noted above, Israel’s discovery of cross-border attack tunnels indicate that the group also conceives an operational, offensive purpose for underground spaces, as well.
Particularly for the tunnels nearest the border, however—the tunnels that Israeli forces have reportedly begun to enter—it is useful to consider them as an integral component of Hezbollah’s defense in depth. This type of defensive plan is an extraordinarily effective one, but requires time to establish. It can consist of minefields and other obstacles, mutually supporting defensive positions, antiarmor ambush sites, preregistered artillery fires, and more, all formed into successive layers from the front lines back and often connected by an integrated network of trenches and bunkers. For Hezbollah, the front line is the Lebanese border with Israel. And tunnels are not only a sort of fully subterranean form trenches and bunkers, but a vital component of the entire defense in depth. Israeli forces’ raids into these tunnels nearest the border, then, are a deliberate effort to strip Hezbollah of this vital component.
Moreover, Hezbollah is the most militarily capable violent nonstate actor in the world. But that capability is largely conventional. The group’s forces are armed and equipped conventionally. It is organized conventionally, as an army. That enormous conventional capability would tempt any organization to use it. And yet in a conventional fight, Hezbollah’s conventional capability, enormous as it is for a nonstate actor, pales compared to the advanced capability fielded by Israel’s forces. History is replete with examples of nonstate groups who chose to fight conventionally and were defeated. Tunnels, then, are a means of staying asymmetric in the face of Israeli military superiority above ground.
Israel’s Plans
So, indeed, why is Israel attempting to use Hezbollah’s tunnels against it, despite their formidable design and utility in the defense? There are several explanations, related to both the Israel Defense Forces’ experience from the 2006 Second Lebanon War as well as the opportunities presented by the successful decapitation strikes last week against Hezbollah’s senior leadership.
Although Israel’s putative defeat in the 2006 war has since been reevaluated by the scholarly community, Israeli forces’ failure to protect its armor against Iranian-supplied, Hezbollah-delivered antitank guided missiles during that conflict’s cross-border raids endures as a salient criticism. If Israel is able to secure Hezbollah’s tunnels, then it can use them as a protected staging area for a new set of cross-border operations. Unlike in 2006, however, Israel now expects to penetrate much farther into Lebanon, probably to clear Hezbollah’s urban rocket firing areas and then occupy them to create standoff for the populated areas of northern Israel. This occupation will absolutely require armor in quantity, and using the tunnels as staging areas for force protection and holding key terrain is a creative preventative from losing armor to the still present antitank missile threat.
Protection of armor is not the only lesson that Israel is likely applying from the 2006 war in its current effort to use Hezbollah’s tunnels. Modern conventional militaries have become increasingly aware of subterranean space as an influential physical dimension of the battlefield, but this space has been effectively conceded, at least narratively, to those who have reason to infiltrate borders—not just terrorist groups like Hezbollah or Hamas, but also drug cartels on the US southern border and the North Korean military across the demilitarized zone, to name a few. To borrow from the tech industry’s lexicon, as with any emergent market for military activity, however, the first adoption of tunnels by nefarious groups has spurred fast following from modern conventional militaries, and the subterranean dimension should no longer be conceded. If nothing else, Israel’s attempted use of Hezbollah’s tunnels shows this evolution.
Finally, Israel’s use of Hezbollah’s tunnels reflects an awareness of the dangers ushered in by decapitation strikes such as the one that killed Hezbollah’s secretary-general, Hassan Nasrallah. Although Hezbollah was certainly thrown into disarray by the sudden loss of its long-standing leader, the group retains a tremendous capacity to regress to unconventional fighting. Historically, when a decapitation strike is followed by a conventional ground campaign, the invading force has difficulty in countering the virulent insurgency that the decapitation spawns. Hezbollah’s tunnels—again, an important means of staying asymmetric—would play a central role in such an insurgency. Securing the tunnels not only robs a future insurgency’s best way to infiltrate northern Israel, but it also signals that the forthcoming ground campaign may not be as conventional as past campaigns. Moreover, the Israelis have the initiative, probably in greater measure than they ever have against Hezbollah and their Iranian backers. If they are going to try something as bold, unexpected, and challenging as using Hezbollah’s tunnels against them, then there is no time like the present.
Amid early reports of direct clashes between Hezbollah fighters and Israeli forces, if a broader invasion is to come, the days, weeks, and perhaps even months ahead will shed more light on how the spaces beneath southern Lebanon’s ground will shape any fighting above it. And yet the case of these tunnels reveals important insights.
Hezbollah’s subterranean network highlights the enduring features that characterize underground warfare. Three in particular stand out. First, tunnels are often a major equalizing factor for an outmatched defending force. During the campaign to recapture vast territory seized by ISIS in Iraq and Syria, almost every major battle took place in cities, where ISIS forces had used existing and newly created subterranean spaces to turn urban areas into fortresses, undergirded by networks of tunnels. Second, in many cases there is virtually no alternative to sending people into tunnels, despite wishful thinking to the contrary (US Army doctrine on subterranean operations warns that “entering and fighting in a subterranean environment is extremely high-ris and units should avoid these fights whenever possible”). In April 2017, the US military dropped the largest nonnuclear bomb in its arsenal on an ISIS tunnel complex in Afghanistan that was too deep to be destroyed by less powerful bombs. Not every military force has such weapons at its disposal, and only on battlefields entirely devoid of noncombatants could its use be contemplated. In other cases, securing tunnels means entering them. And third, for military forces, there is no substitute for experience. Underground environments are so deeply unique that lessons must be learned practically. Israeli forces have benefited from more extensive experience than arguably any other military in the world. For others—like the US military—deliberate efforts to learn from the experience of others and retain lessons from its own history are vital.
In terms of how Hezbollah tunnels will factor into any broader Israeli campaign, notwithstanding the tunnels’ utility to Israel’s interest in protecting its armor and mitigating the dangers inherent to a decapitation strategy, it still has to execute the expected ground campaign to clear the rocket sites and establish a buffer zone. Thus, despite the novelty and boldness of Israel’s current efforts to use Hezbollah’s tunnels, they are simply a new shaping operation to a war that we have seen before. That war and whatever decisive operations come with it may also show something new, however. Unlike in 2006, Israel’s actions against Hezbollah’s tunnels signal a certain permanence about the ground campaign—an intent, perhaps, to finally solve the problem of Hezbollah and the sanctuary it enjoys from Lebanese territory and Iranian patronage. In this context, Israel’s use of Hezbollah’s tunnels does not just shape a future physical buffer, but a psychological one as well.
It is also important to acknowledge the forces sent as part of the reconnaissance and initial raiding forces into southern Lebanon were the same battle-experienced units adapting, innovating, and in some cases dominating against Hamas tunnels in Gaza, such as the 98th Division, the members of which were credited with becoming such experts in underground warfare that they shifted the paradigm of tunnels in Gaza, from being an obstacle to being an advantage for the attacking Israelis.
Finally, the Israel Defense Forces have also learned the two-pronged lesson that subterranean spaces are a fundamentally unique environment, but that no two tunnels are the same—in purpose, construction, advantages, or disadvantages. The challenge is crafting an approach to underground warfare that is both optimized for unique challenges and flexible enough to adapt to unique conditions that meaningfully distinguish, for instance, Hamas tunnels in Gaza and Hezbollah tunnels in southern Lebanon. Arguably, no military in the world has made more progress on this front than the Israel Defense Forces. The specialized subterranean capabilities housed in its Yahalom Unit are an example. Part of the Israeli Combat Engineering Corps, its organization, training, and equipment rightly reflect that at its core, underground warfare is as much an engineering challenge as a strictly combat one.
The net total of the impact of Hezbollah’s tunnel network on the conflict above ground will only become clear as that conflict unfolds. But Israel’s raids into the tunnels ahead of any larger-scale offensive are a clear acknowledgement of a simple reality: the fight to control the tunnels and deny their control to Hezbollah is a necessary component of any campaign against the group. A war might not be won exclusively in the tunnels, but it cannot be won without accounting for them.
Colonel Patrick Sullivan, PhD, is the director of the Modern War Institute at West Point.
John Spencer is the chair of urban warfare studies at the Modern War Institute at West Point.
John Amble is the editorial director of the Modern War Institute at West Point.
The views expressed are those of the authors 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