October 6, 2016

TSG IntelBrief: The Looming Assault on Mosul

• The long-awaited assault on the Islamic State’s Iraqi stronghold of Mosul is set to begin in the coming months.

• When faced with overwhelming force, the Islamic State has often used a combination of irregular warfare and tactical retreats to impede advancing forces, while saving the bulk of its military force from destruction.

• Given the strategic value of Mosul, however, the group may mount a much more determined defense, risking the defeat of its military center of gravity in Iraq.

• The operation to retake Mosul represents a major test of the Obama administration’s grand strategy in the fight against terrorism.


After more than two years, all indications suggest that the long-awaited assault on Mosul—the Iraqi stronghold of the so-called Islamic State—will begin in earnest in the coming months. Over the last several months, key terrain around the city has been seized, political agreements have been struck between Iraqi and Kurdish security forces, and the international community has stepped up its support for the assault—including the deployment of an additional 600 U.S. troops, bringing the total to approximately 5,000. While the operation’s start date has been delayed repeatedly, the Iraqi government stated that it intends to retake the city by the end of 2016. Facing an unprecedented combination of Iraqi and international firepower, the question now concerns the level of resources the Islamic State is willing to gamble in defense of one of the crown jewels of its so-called caliphate

When faced with the prospect of overwhelming force in other strategic cities, the Islamic State has often preempted a strategic defeat with a tactical retreat, thus preserving the majority of its fighting force. Typically, as enemy forces close in on the city, the bulk of the group’s fighters are exfiltrated, leaving behind a relatively small but lethal cadre of fighters specially trained as snipers, suicide bombers, and IED specialists, meant to impede the enemy advance while causing as many casualties as possible. This strategy has been witnessed in recent battles in Manbij, Syria and Sirte, Libya. The ultimate goal is not to attempt to hold territory—which is likely futile—but to exact a massive cost on the enemy without risking the bulk of the group’s fighters. 

However, there are reasons to believe that the Islamic State may mount a more robust defense of Mosul than it has in other strongholds. The city is the bedrock of the group’s efforts in Iraq; its strategic value—in both military and propaganda terms—should not be underestimated. The Islamic State has had years to bolster the city’s defenses, making it a uniquely challenging urban battlespace for an invading force. According to Iraqi and Kurdish officials, fighters have hardened the city’s defenses in medieval fashion, with interconnected tunnels, deep surrounding trenches, and an oil-filled moat. IEDs have reportedly been placed throughout the city to slow advancing troops. The thousands of Islamic State fighters that remain in Mosul have reportedly been ordered to hold the city to the best of their ability, and to carry out mass killings and destruction in the wake of their retreat. 

Should the Islamic State choose to make a stand in Mosul by committing the majority of its forces in Iraq to the city’s defense, the military and humanitarian cost of retaking the city would be an order of magnitude greater than that seen in other battles against the Islamic State. The UN recently said that the battle for Mosul could produce ‘one of the largest man-made disasters’ in years. However, such a battle could end with the destruction of the Islamic State’s military center of gravity in Iraq, dealing the group a decisive blow and damaging its long-term prospects there. Conversely, the group’s leadership could choose to preserve its long-term offensive capabilities by enacting a tactical retreat, and mounting a token but still brutal defense of the city. While such a scenario would lessen the military and humanitarian task of retaking the city, it would also foreshadow a longer fight to strategically defeat the Islamic State’s forces in Iraq. 

The assault is a major test of the Obama administration’s grand strategy in the fight against terrorism. This strategy emphasizes the use of local forces—backed by a light footprint of American airpower and Special Operations Forces (SOF)—to retake territory held by terror groups, while simultaneously facilitating political reforms meant to ensure long-term stability. Despite the recent political comity inspired by the looming assault on Mosul, Iraqi politics remain in a state of turmoil, suggesting that military efforts to defeat the Islamic State are outpacing political ones. While it is likely that Iraqi security forces will eventually take Mosul, the domestic political turmoil threatens their ability to hold it in the long-term. While there have been agreements between the myriad forces who will take part in the assault—including Kurdish Peshmerga, Shi’a militias, Sunni tribal militias, and the regular Iraqi Army—these forces’ divergent political goals threaten the kind of long-term political cooperation required to prevent the Islamic State’s resurgence.


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