Preparing for Warfare’s Subterranean Future


Amidst the myriad mistakes associated with the Iraq War, perhaps none were as costly in terms of lives of U.S. personnel as the failure to anticipate the threat posed by improvised explosive devices (IEDs) and, subsequently, to rapidly develop technologies capable of detecting and defeating the insurgents’ deadly innovation. Despite the extensive use of IEDs in conflicts in Northern Ireland, Afghanistan, and Southern Lebanon, and the loss of U.S. personnel to IEDs in Somalia, U.S. policymakers and the military were caught unprepared for these devices that by one estimate were responsible for 64 percent of all U.S. combat deaths through 2007.

The defense community, however, has an opportunity to avoid repeating this error in regards to another potential operational threat if it does a better job drawing lessons from last year’s conflict between Hamas and Israel than it did from the various guerrilla conflicts of the 1980s. Operation Protective Edge demonstrated both the tactical challenges and strategic threat posed by subterranean warfare (i.e. tunnels), which is likely to proliferate in the coming years as weaker combatants seek to evade detection and targeting by air assets.

To be sure, Hamas’s extensive use of tunnels during last summer’s conflict was not a revolutionary development in warfare. For hundreds of years, military forces have attempted to gain the upper hand over their adversaries by maneuvering beneath them. Medieval soldiers would dig tunnels deep under an enemy’s castle walls, collapse the tunnel, and bring down the castle along with it. Similarly, in World War I both the Germans and Allied forces dug lengthy tunnel networks to be exploded under each other’s trenches, with their mining operations frequently coming close enough to each other that they conducted tunnel-versus-tunnel attacks. Jewish resistance fighters in the Warsaw Ghetto uprising were so effective at using the city’s sewer system to outflank the Wehrmacht and attack from the rear that German commanders reported their forces developed “sewer paranoia.” During the Vietnam War, the Viet Cong used tunnels to move troops and establish massive logistics bases, with the Cu Chi network northwest of Saigon alone consisting of 150 miles of tunnels. And in Iraq, insurgents in al-Qaeda strongholds such as Anbar and the Dora and Ameriya neighborhoods of Baghdad were able to plant IEDs in sewers large enough to flip Bradley fighting vehicles with deadly results.

Hamas’s extensive use of tunnels during last summer’s conflict is only the most recent example of a combatant attempting to gain advantage by going underground. In June 2006, a joint Hamas/Jaish al-Islam unit infiltrated from Gaza into Israel through a tunnel whose opening was about 100 meters from the border in Israeli territory, killing two Israeli soldiers and kidnapping Gilad Shalit, who was eventually traded for more than 1,000 Palestinian prisoners. Between the end of Operation Cast Lead (January 2009) and Operation Pillar of Defense (November 2012), Hamas expanded its system of tunnels and underground bunkers throughout the Gaza Strip, by one estimate devoting 40 percent of its budget to the project. This extensive tunnel network — which one Israeli general said stretched for “dozens and dozens of kilometers” — offered cover and concealment for infrastructure, command functions and commanders, forces, weapons, and ammunition. As noted in a recent report by five retired generals sponsored by JINSA, this network made it almost impossible for Israeli airborne intelligence, surveillance, and reconnaissance (ISR) assets to detect or prevent movement of fighters, supplies, munitions, and weapons. The tunnels beneath protected sites, such as the Shifa Hospital in Gaza City, are believed to have housed Hamas’s senior operational leadership during the fighting, thereby increasing the terrorist group’s defensive resiliency and prolonging the conflict by making it more difficult for Israel to target a key Hamas center of gravity. The tunnels were also integral to Hamas’s rocket operations, as they opened briefly to launch rockets and then immediately closed to prevent the Israeli Defense Forces (IDF) from detecting the launchers’ location. This made it extremely difficult to detect and target them in real time, and allowed Hamas to continuously launch rockets into Israel throughout the conflict.

More significant, perhaps, were the 32 “attack tunnels” Hamas had dug to infiltrate Israeli territory, 15 of which reached as far as 1.5 miles into Israel at the start of Operation Protective Edge. In addition to allowing Hamas to conduct coordinated raids on multiple targets inside Israel, these tunnels gave Hamas the ability to flank the IDF from the rear. This created a tactical challenge for the IDF during the operation by redefining the concept of the front line. IDF units sometimes found themselves two kilometers into Gaza destroying the entrance to a tunnel only to have Hamas assault squads emerge from the same tunnel into Israel and threaten Israeli civilians. These squads executed six tunnel-based infiltration operations, engaging Israeli forces four times and killing 11 Israeli soldiers.

Hamas’s attack tunnels proved difficult to target and destroy. Israeli forces knew where they originated from within Gaza. Yet despite examining some 700 projects for tunnel detection or blockage systems over the past decade — to include “dozens of millions of dollars” spent on seismological, magnetic, and radar systems — the IDF did not possess a technology capable of determining where they went or their exit points within Israel. Because of the tunnels’ depth — sometimes descending as far as 35 meters (115 feet) below the surface — the technologies used by U.S. agencies to find smuggling tunnels under the Mexican border were not applicable to the Israeli-Gaza border.

The inability to remotely and accurately detect these tunnels ultimately required the IDF’s major ground incursion into Gaza. Initially, Israel’s political leadership sought to neutralize the tunnels solely through bombing. But this proved ineffective. Air strikes only obscured the tunnel entrances and failed to destroy their multiple branches or the assault teams waiting underground. When it was determined that ground troops were necessary to address the attack tunnel threat, IDF maneuver units advanced a couple kilometers into Gaza through prepared defenses in urban terrain, operations that resulted in the majority of IDF casualties.

Once the tunnel entrances were secured, other problems frustrated efforts to destroy the tunnels. A shortage of excavators and drillers meant the tunnels had to be dealt with sequentially rather than simultaneously, prolonging the ground operation. Once on-site, robots proved ineffective as they lost communications past 100 meters into the tunnel. Consequently, IDF engineers were sometimes only able to destroy the first or last 200 meters of a tunnel, which can easily be re-excavated. The air pressure at that depth reduced the effectiveness of various explosives, adding to the challenge of exploding the tunnels. It sometimes took 16 tons of Emulsion (an explosive material injected into tunnels from a truck-operated system) and 60 mines to destroy a single kilometer of tunnel. Although successful in accomplishing its stated objective of destroying the attack tunnels, the ground offensive came at a significant cost, with the IDF suffering more casualties than in any operation since Hamas seized power in Gaza in 2007.

The challenges posed by tunneling are by no means an exclusively Israeli problem. Given the U.S. military’s technological dominance on the battlefield, our future adversaries will seek to create similar asymmetries in order to counter U.S. air superiority. As precision guided munitions allow U.S. forces to become increasingly adept at engaging targets in heavily populated urban terrain, the next logical evolution for opposing forces will be to move underground.

There is already significant evidence that other rogue states and non-state entities either possess or are developing such capabilities. Defectors have reported that the North Koreans have built 21 infiltration tunnels under the Demilitarized Zone into South Korea, although to date only four have been discovered. For more than a decade, and possibly with North Korean assistance, Iran has been building extensive nuclear facilities in networks of underpasses and bunkers across the country to protect them from potential Western airstrikes. Similarly, one reason Israeli air power was not decisive during the 2006 Second Lebanon War was because of Hezbollah’s tunneling capabilities that provided the militia with an extensive system of underground bunkers and rocket-launch sites, including one with air conditioning, a cafeteria, dorms, medical facilities, and three-foot-thick cement ceilings. Moreover, for years residents of villages in northern Israel have claimed to hear drilling noises underground, raising as-yet-unconfirmed suspicions that Hezbollah is also constructing offensive-oriented tunnels. Hezbollah is also allegedly digging tunnels for drug cartels on the Mexican-American border. Finally, estimates place the underground network dug by Syrian rebels to avoid the Assad regime’s airpower and snipers at between 500-1,000 tunnels, including one that was packed with explosives and detonated under the Syrian Air Force Intelligence Directorate headquarters in Aleppo on March 4th killing 20 government soldiers, one of several such rebel attacks that harken back to subterranean warfare’s medieval roots.

Two bills have recently been introduced in the House of Representatives to address this challenge. On March 10, Representatives Gwen Graham (D-FL) and Doug Lamborn (R-CO) proposed the United States-Israel Anti-Tunnel Defense Cooperation Act (H.R. 1349), and on March 30 Lamborn introduced The Partnering to Detect and Defeat Tunnels Act (H.R. 1649). Both bills seek to establish a research and development partnership between the United States and Israel similar to that which produced the successful Iron Dome missile defense system, only directed towards detecting and destroying tunnels such as those employed by Hamas beneath Gaza. (The second bill is both more specific in terms of determining U.S. government responsibilities and more expansive in terms of geography to incorporate South Korea and other allies.) Both bills merit serious consideration and eventual passage, not only as a means of reiterating the strength of the U.S.-Israeli security cooperation despite the spate of recent political controversies — both genuine and contrived — between the Obama administration and Prime Minister Benjamin Netanyahu, but also because of the high probability that U.S. forces will eventually encounter an adversary seeking to exploit the subterranean domain against us.

In addition to expeditiously passing the anti-tunneling bills noted above that have been sent to the relevant committees, tunnel detection technology — to include airborne-mounted platforms — must be rapidly developed to counter the increased use of tunnels. U.S. tunneling technology also needs to be developed, for clearing or exploiting enemy tunnels will be difficult if access is limited to only tunnel entrances and exits. A tactical tunneling capability to rapidly dig our own entrances into enemy tunnels — while being protected underground ourselves — can negate the effects of enemy defenses and booby traps. Finally, the Department of Defense should conduct extensive testing of thermobaric weapons — which have been used successfully against caves in Afghanistan — against tunnel networks.

If the retired generals that studied the Gaza conflict are correct that subterranean operations — both for offensive and defensive purposes — may constitute a separate domain of warfare “equivalent to land, sea, air and cyber domains, requiring its own tactical doctrines,” the United States cannot afford to be caught unprepared. We owe it to our servicemen and servicewomen to learn the lessons from recent conflicts and develop responses to the threats posed by tunneling before we commit them to battle.


Benjamin Runkle is a former Defense Department official, Director on the National Security Council, and Professional Staff Member on the House Armed Services Committee. He is a veteran of Operation Iraqi Freedom and the author of Wanted Dead or Alive: Manhunts from Geronimo to bin Laden.


Photo credit: Israel Defense Forces