Recent on-the-ground reports from Northern Iraq, as well as statements from senior U.S. and Iraqi commanders, clearly telegraph the next phase of the ongoing campaign against the Islamic State: the battle to retake Mosul. As Iraqi forces, backed closely by U.S. advisors, prepare for the imminent clearance of the strategic city, they should heed the lessons learned from previous efforts to wrest control of Mosul from the Islamic State. When facing a major clearance operation, the group has often managed to go “underground” rather than fight a conventional military force head on. This age-old insurgent technique enabled the Islamic State’s predecessor, the Islamic State of Iraq (ISI), to survive years of robust, sustained U.S. and Iraqi counter-terrorism operations in Mosul from 2004 to 2009 and re-emerge when U.S. forces left the city in 2010.

As clearance operations get underway in Mosul, the Islamic State will likely replicate this approach, deactivating and dispersing its military units and reinforcing its intelligence, security, administrative, and financial groups. The coalition of Iraqi and U.S. forces must anticipate this adjustment, and prepare to execute a deliberate campaign targeting Islamic State “enabler” elements, which may operate just under the radar of coalition and Iraqi forces, but in plain sight of the all-important civilian population. If the coalition does not do this, the group could survive yet again – maintaining its stranglehold on Mosul through extortion, intimidation, and assassination only to resurface there once coalition forces shift their focus elsewhere.

The Coming Liberation?

Virtually every analyst and pundit agrees that retaking Mosul from the Islamic State is a necessary and important next step for the coalition of Iraqi-government backed forces, many of which are already positioned in areas east and south of the city, such as Qayyarah and Sharqat. However, much of the recent media coverage of the upcoming Mosul operation, in hyperbolic fashion, has characterized it as the pivotal battle against the Islamic State, despite the fact that the group continues to control considerable territory in Iraq and Syria.

More seasoned experts and national security policymakers understand that the upcoming clearance operation will in fact be only the first phase of a complex “clear, hold, and build” campaign that will play out over months or years. A consensus narrative has emerged from these experts that the initial “clearance” of Islamic State forces from Mosul will be relatively easy, at least compared to the much more difficult task of establishing some semblance of enduring stability in the operation’s wake. Drawing on hard-won experience from the last decade plus in Iraq, many experts have emphasized the importance of reconstruction, political reconciliation, and reestablishing representative governance for long-term success.

However, before too quickly turning its attention to the necessary but complex, difficult, and time-consuming task of re-establishing governance in the city, the counter-ISIL coalition must identify, disrupt, and ultimately defeat the Islamic State’s enabler networks – which will continue operating in Mosul’s underground, even after the overt military presence of the organization is reduced. This will allow Iraqi and coalition partners to consolidate their initial gains, maintain pressure on the Islamic State and, over time, degrade its ability to self-finance. Only once the Islamic State’s underground network is fully defeated will there be a real chance for enduring security and stability in Mosul.

The Past is Prologue: Mosul, 2005-2010

In order to better anticipate how the Islamic State is likely to respond and adjust to the upcoming clearance operations in Mosul, one need look no further than the group’s predecessor, al-Qaeda in Iraq (AQI), which subsequently became ISI (hereafter referred to as “AQI/ISI” for purposes of clarity and simplicity). The Islamic State is a direct descendant of AQI/ISI, and shares many key characteristics with its predecessor, from ideology and religious philosophy to organizational structures and attack methodologies. Most significantly, many of the top leaders of the Islamic State, including the current leader of the group Abu Bakr al-Baghdadi, were senior leaders within AQI/ISI.

Careful study of the group and its past operations, especially in Mosul, offers immensely valuable insights for military planners and policymakers. Along with several colleagues, we recently undertook an in-depth analysis of AQI/ISI, publishing a RAND Report entitled Foundations of the Islamic State: Management, Money, and Terror in Iraq, 2005-2010. The report draws from more than 140 recently declassified documents to present a comprehensive examination of the organization, finances, territorial plans, bureaucracy and management, and finances of the Islamic State’s predecessors in Iraq. One of our most compelling findings was the critical role that AQI/ISI’s functional support groups played in the organization’s effectiveness and resilience. We were able to construct a clear blueprint for how AQI/ISI developed its extensive underground support network in Mosul, which proved critical in setting the conditions for the Islamic State’s rapid seizure of the city in June 2014. This same robust network, which functions similarly to a dominant local criminal gang, still thrives in Mosul and could enable the Islamic State to remain resilient despite the success of any upcoming clearance operations.

Based on our analysis of AQI/ISI’s past behavior, we urge analysts and policymakers to be cautious before declaring how quickly or easily coalition forces will “defeat” the Islamic State in Mosul, and elsewhere. The group has repeatedly proven its ability to morph from a “statelet,” with an overt military and governance capability, to a covert terrorist organization, operating underground to preserve its control and influence over the local population while minimizing losses to the group. In fact, a May 2016 speech by now-deceased senior Islamic State leader Abu Muhammad al-Adnani foreshadowed this exact approach, harkening back to the group’s previous success in going underground.

Breaking Down the Underground

Drawing upon captured documents and media from AQI/ISI between 2005 and 2010, our team constructed a clear picture of how the group organized and operated across time and space in Iraq, and, in particular, of how they established control and influence over a city or region. This process always began with the establishment of a robust underground structure – comprising intelligence and security, extortion and assassination, sharia (Islamic law), administrative, and media groups – before ever establishing an overt military operational structure. By establishing this broad underground base supported by a robust set of functional groups, AQI/ISI was much better positioned to both exert and maintain control and influence in a particular area.

Mirroring the original organizational design outlined in the early days of al-Qaeda’s formation, AQI/ISI designed its structure as a hierarchy in which each level practiced considerable top-down control over subordinates who administered a bureaucratic organization with strict standard operating procedures. AQI/ISI, in late 2008, was a standard multidivisional hierarchy, commonly known as an “M-form,” in which a central management structure with functional bureaus is replicated at multiple lower geographic levels. This structure and organization resulted in a surprisingly bureaucratic and rigid operating model, almost all of which has been carried over to the successor Islamic State group.

The graphic above provides a snapshot of how AQI/ISI was organized in Mosul during 2007 and 2008, at the peak of the group’s power and influence. There were multiple functional emirs who, under the direction of an overall emir at the city level, were responsible for a diverse set of tasks and managed a series of geographically focused functional cells. In addition to the military groups, which were extremely active in conducting violent attacks at that time, there were also several other key functional groups including: 1) security, which also included intelligence cells, and was responsible for tracking and intimidating local security, political, and business leaders; 2) administrative, which often had responsibility for financial matters, and oversaw all logistics, recruiting, and personnel; 3) media, which conducted information operations and produced propaganda; and 4) sharia, which formed relationships with local religious leaders and provided religious justification for the group’s attacks.

AQI/ISI’s well-defined structure and organizing principles ultimately carried over to the group’s operations, which also tended to follow strict rules and procedures. This proves especially useful for analytical purposes, allowing planners to develop historically-based hypotheses for how the group will operate in the future. In one particularly detailed strategy document, probably written in late 2007 or 2008, an AQI/ISI leader describes a plan for consolidating control over Husaybah, a city in Anbar province. The deliberate and sequential process outlined in this document closely mirrors the standard process that AQI/ISI used throughout countless cities in Iraq, both small and large, to establish control over an area:

Infiltrate the city and surrounding areas and establish safe-houses, which will be occupied by more senior, experienced members of the group;

Establish an intelligence network by recruiting local informants who will be managed by a set of trained AQI/ISI intelligence operatives. Conduct surveillance of important buildings and influential leaders, and develop a comprehensive intelligence picture of the city;

Establish security groups that will conduct an intimidation and assassination campaign against government officials, police and military leaders, influential political and tribal leaders, and business owners;

Establish extortion and other criminal revenue-generation processes, which enable the group to begin to self-finance;

Develop administrative and financial groups that enable more robust command and control, logistics, and recruiting;

Develop relationships with local religious leaders, and establish sharia groups to approve attacks, issue fatwas, and support recruitment;

Establish media groups to conduct information operations and produce media content;

Establish regional and specialized military cells to conduct violent attacks.

AQI/ISI successfully repeated this process time and time again as it established control over urban and rural areas throughout Iraq from 2005-2010. Based on extensive on-the-ground reporting from Mosul and other Islamic State-occupied cities, as well as careful analysis from leading experts and scholars, it’s clear that the Islamic State is following this same blueprint today. In Mosul, the group has now had over two years since its initial seizure of the city to further reinforce these enabler groups.

Countering the Islamic State Underground

In anticipation of the impending coalition operations in Mosul, recent reports indicate that the group has already begun to revert underground, ramping up its security efforts through a campaign of intimidation and assassinations. Just last week, the Islamic State executed 56 residents of Mosul who were accused of fomenting rebellion ahead of the looming offensive. The coalition should not mistake the Islamic State’s reversion from overt semi-state to covert terrorist network, which is a deliberate strategic choice, for any sort of lasting defeat of the group. Instead, the coalition should press its initial military gains and launch a comprehensive effort to destroy the Islamic State’s entrenched and resilient underground enabler network. To ensure the success of this critical effort, the anti-Islamic State coalition should do the following.

Success is dependent on achieving a granular understanding of the Islamic State’s underground network and “standard operating procedures,” with a particular emphasis on outlining the key leaders and operatives of the group’s intelligence, security, and finance components. Coalition planners should carefully study how the Islamic State’s predecessor reestablished its security, intelligence, and extortion infrastructure in Mosul after the U.S. withdrawal from the city in 2010. In doing so, they can draw upon a fairly extensive set of scholarly analyses of AQI/ISI, including our recent report, as well as what is likely a rich array of classified documents and analyses from the last decade of operations against the group. Without taking the time to carefully construct a full picture of the Islamic State’s network throughout Mosul and wargame the group’s likely courses of action after the initial defeat of its military groups, the coalition risks missing a major opportunity to deliver a lasting defeat.

Armed with a comprehensive understanding of how the Islamic State will likely look to reassert control over the city and a clear picture of the key leaders of each of these enabler groups, the coalition should formulate and execute an effective targeting campaign. Coalition planners and policymakers should build upon the lessons learned from previous successful efforts against AQI/ISI. In particular, the U.S.-led coalition’s expertly orchestrated leadership targeting campaign against AQI/ISI from 2007-2009 was successful because it prioritized the group’s enabler elements and focused on striking at the network layer level, rather than the individual level. Although some level of debate and disagreement remains among scholars and analysts, there is a growing body of academic research that has validated the effectiveness of leadership targeting, especially when orchestrated in a manner that eliminates both mid- and high-level leaders from across multiple functional wings of the group in rapid succession. This approach is neither fast nor simple, relying on accurate and timely intelligence as well as extensive counterterrorism strike resources, but is necessary to achieve enduring effects.

In parallel, the counter-ISIL coalition should stand up a specialized intelligence and enforcement group focused exclusively on detecting and disrupting the group’s illicit financial activities, such as extortion, illegal taxation, and black market sales of oil and other valuable resources. This effort will be complementary to the leadership targeting effort, but requires an inherently different approach and specialty training. The work of this group more closely parallels traditional detective work, much like what the FBI or customs enforcement agencies do on a daily basis to disrupt criminal gangs and drug traffickers. The coalition should build upon the previously successful model of the joint, interagency “threat finance cells” that were created in Iraq and Afghanistan, expanding them to more effectively tie in local partners who can provide valuable intelligence and on-the-ground resources to disrupt the Islamic State’s finance activities. Finding reliable, high-quality local partners to execute these activities can be difficult and uneven, but will be critical for success. If effectively executed and synchronized with leadership targeting efforts, this capability could undercut the Islamic State’s vital capability to self-finance.

Finally, the coalition should support efforts not only to build capacity, but also trust in local political and law enforcement institutions. The social and political landscape in Mosul is complex and likely to be contentious long after the end of the Islamic State. The capacity and credibility of outsiders to forge local solutions is limited. Both the military’s advisory mission and the U.S. Embassy’s efforts to build and maintain strong diplomatic relations at all levels of government will require an earnest, long-term, and well-resourced American commitment.

The clearance of Mosul – the Islamic State’s declared capital in Iraq, and the group’s long-time center of gravity – is vital for the ultimate defeat of the group. Even more important, however, will be what comes next. While policymakers should dedicate significant energy and resources to re-establishing governance and rebuilding the city’s shattered infrastructure and economy, the counter-ISIL coalition must first consolidate and fully exploit its initial military gains. The coalition cannot afford to repeat the mistakes of the last decade, allowing the group to survive under the radar only to re-establish influence and control. Careful analysis of the Islamic State’s previous strategic adaptations should inform a comprehensive coalition strategy to destroy the Islamic State’s robust underground enabler networks. As we have learned, this approach will not be easy or quick, but it will be necessary for long-term success against the group.

Patrick Ryan is a West Point graduate and former U.S. Army intelligence officer. He served two combat tours in Iraq from 2005 to 2009, including 15 months in Mosul where he led a team of intelligence analysts targeting senior Islamic State of Iraq leadership. Ryan earned an M.A. in Security Studies from Georgetown’s Security Studies Program and is a Term Member at the Council on Foreign Relations.

Patrick B. Johnston is a political scientist at the nonprofit, nonpartisan RAND Corporation. He has been published in numerous peer-reviewed journals, news outlets, and has given congressional testimony on ISIL financing. Johnston completed his Ph.D. in political science at Northwestern University and held fellowships at the Harvard Kennedy School, Stanford University, and the United States Institute of Peace.