Cave and tunnel complexes that the Islamic State started constructing well before the collapse of the caliphate have become a core element of the group’s asymmetric war fighting strategy. In the Hamrin mountain region, an area that straddles Diyala, Salah ad-Din, and Kirkuk governorates, the Islamic State has put considerable effort into constructing vast rural tunnel networks with weapons depots and foodstuffs well ensconced in both natural and man-made caves. The cave complexes, insulated with USAID tarps once intended for Iraqi internally displaced persons, are being discovered throughout this region. The caves serve as rugged redoubts from which the group wages guerilla war against the Iraqi state and its affiliated militias. As Iraqi and local ground forces supply geolocations, Combined Joint Task Force-Operation Inherent Resolve (CJTF-OIR) has been carrying out airstrikes aimed at dismantling the Hamrin tunnel network along with outlying bunker positions to smash the infrastructure undergirding the insurgency.
This article is based in part on the author’s field reporting in Iraq in early 2018. Iraqi and pan-Arab news outlets have also reported on the ongoing counterinsurgency operations in the Hamrin Mountains. It is an area where al-Qa`ida in Iraq (AQI) in the last decade had a significant freedom of movement, even with a large U.S. troop presence in Iraq. It is now a significant safe haven for the Islamic State.
In their efforts to flush out Islamic State militants, Iraqi Security Forces (ISF) and Shi`a militiamen incorporated under the Hashd al-Shaabi umbrella have been reaching the Hamrin foothills by Humvee and Toyota Hilux and then dismounting to scale higher elevations on foot while backed up by Iraqi Army helicopters. Sunni Arab tribal militias, known as Hashd al-Asha’iri, are also involved in security efforts around the Hamrin Mountains. In contrast to many Shi`a Arab fighters in Hashd al-Shaabi militias, Hashd al-Asha’iri are most often of local origin and allied to regional tribal leaders; they provide both indigenous intelligence and credibility in insurgency-affected districts of federally controlled northern governorates where fighters from the Shi`a-majority south are viewed as outsiders while also enlarging the security footprint of the ISF and the Hashd al-Shaabi. The current conflict in the greater Hamrin region is primarily a shadow war with little direct kinetic contact between opposing forces. Holding the high ground, jihadi militants have been able to retreat deeper into the hills as ISF and Hashd al-Shaabi expeditionary forces have approached at a distance from the lowlands.