The campaign to liberate Mosul from Islamic State (ISIL) may still be in its early stages, but it has already revealed several tactical dilemmas that will have significant consequences for future military conflicts in the Middle East. Last month, ISIL used a small drone to attack Iraqi forces participating in the offensive , killing two Kurdish fighters when explosives disguised as a battery were detonated. Although other attempts to deploy “flying IEDs” have been less successful, the U.S. commander in Iraq, Lieutenant General Stephen Townsend acknowledged that this capability represented a “pretty thorny problem” and that, “We expect to see more of this.”
At the same time, U.S. and Iraqi forces liberating the villages around Mosul have discovered what one U.S. military official described as “ quite extensive tunneling systems ,” the longest of which – according to Iraqi commanders – stretches for six miles. An Iraqi special forces commander said , “It’s like we are fighting two wars in two cities. There’s the war on the streets and there is a whole city underground where they are hiding.” These village-to-village tunnel networks are wired for electricity, contain stockpiles of food and ammunition, and are tall and wide enough for supplies and fighters to be transported across the battlefront by motorcycle. Given that ISIL has had two years to dig in within Mosul, an even bigger subterranean labyrinth likely awaits inside the heavily fortified city.
To be sure, ISIL is not the first extremist group to utilize these asymmetric tactics. In 2006 Hezbollah flew at least three Mirshad drones into Israel , each carrying a payload of approximately 22 pounds of explosives packed with ball bearings to increase their lethality, and during 2014’s Operation Protective Edge, Hamas made several unsuccessful attempts to infiltrate Israeli airspace with unmanned aerial vehicles (UAVs.) The Palestinian terror group, however, has enjoyed greater success underground than in the air. In June 2006, a joint Hamas/Jaish al-Islam unit infiltrated from Gaza into Israel through a tunnel whose opening was about 100 meters inside Israeli territory, killing two Israeli soldiers and kidnapping another. By 2014 Hamas had constructed 32 assault tunnels – fifteen of which reached as far as 1.5 miles into Israel – to execute six tunnel-based infiltration operations that killed eleven Israeli soldiers. Elsewhere, Taliban forces have exploited karez networks – traditional underground irrigation systems – in Afghanistan’s Kandahar and Helmand provinces, and in 2011 African Union forces in Mogadishu discovered an extensive system of tunnels used by Islamist insurgents.
In fact, ISIL itself has attempted to employ these capabilities prior to the battle for Mosul. The terrorist proto-state has been using UAVs for surveillance and for filming propaganda videos at least since December 2014, with coalition forces first destroying an ISIL-controlled drone in March 2015 . Sometime earlier this year, ISIL began crudely strapping explosives to these UAVs as early as last December. Similarly, coalition forces have discovered extensive tunnel networks in other cities from which ISIL has been driven, including Ramadi, Sinjar, and Fallujah in Iraq, Manjib in Syria and Sirte in Libya .
Yet even if ISIL’s use of UAVs and tunnels is not in itself revolutionary, it is significant, as they demonstrate how unconventional adversaries can leverage low-tech solutions to overcome technological advantages enjoyed by conventional militaries. For example, given states’ technological dominance on the battlefield – including precision guided munitions that allow U.S. and Israeli forces to become increasingly adept at engaging targets in heavily populated urban terrain – the next logical evolution for opposing forces is to move underground into tunnels that provide combatants with the ability to counter an adversary’s air superiority. 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 . A decade later, estimates place the underground network dug by Syrian rebels to avoid the Assad regime’s airpower at between 500-1,000 tunnels .
Further, as Hamas has repeatedly demonstrated, tunnels allow unconventional forces to evade air surveillance in order to conduct offensive operations. During Operation Iraqi Freedom, 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. The Free Syrian Army reportedly used a tunnel to infiltrate a government military base near Erbin in 2013 , and in March 2015 a tunnel packed with explosives was detonated under the Syrian Air Force Intelligence Directorate headquarters in Aleppo killing at least 20 government soldiers . Later that month, ISIL forces detonated a tunnel bomb containing seven tons of explosives under an Iraqi army headquarters in Ramadi , killing 22 people. Moreover, both Hamas in 2014 and ISIL in the battle around Mosul have used tunnels to threaten the rear flank of advancing forces. As an Iraqi colonel complained, “Now it’s hard to consider an area liberated, because though we control the surface, ISIS will appear from under the ground , like rats.”