This battlefield assessment of the impending fight for the Islamic State-controlled city of Mosul surveys the battlefield’s geography, examines the capabilities of the numerous states and groups that have committed resources to the battle, and explains the steps taken by both sides to date. This report concludes that while the Islamic State is outmanned and outgunned, it is in a highly advantageous defensive position that will enable it to inflict serious enough casualties on the attacking force that any coalition victory will be a hollow one.

  • Current reports tracking progress of the coalition’s attack on Mosul are exaggerated and overly optimistic; anti-IS forces haven’t reached the city yet and are beginning to face resistance as they approach.
  • The battle for Mosul will be a textbook case of urban warfare, resulting in high casualties for the attacking force along with high civilian casualties.
  • The coalition against the Islamic State is formidable, but it is plagued by internal dissension and mistrust among its actors.
  • The Islamic State does not have to win the battle to achieve strategic goals; the higher the cost it inflicts on the attacking forces, the more reluctant regional actors will be to repeat this type of attack on IS in other urban strongholds.


The battle for the areas around Mosul began on Oct. 18. Although the battle for Mosul itself has yet to begin, it is fast approaching. Coalition forces, led by the Iraqi Security Forces (ISF) and Kurdish peshmerga forces, are advancing on the city from the north, east and south. They first met resistance on Oct. 19, roughly 10-25 miles outside the city in all directions, and remain preoccupied with IS resistance as of this writing. The Islamic State’s opponents are leaving the western axis conspicuously open, hoping that IS will cut its losses and run into the desert to make a clear target for U.S. airstrikes. However, the Islamic State is not likely to withdraw. IS has already retreated as far as it can, and now it means to make its opponents pay dearly for every square mile of the city they try to take.

Battlefield Mosul

Mosul is a large city divided by the Tigris River. Before it was taken by the Islamic State in June 2014, Mosul was the second most populous city in Iraq. It is hard to say how the IS takeover affected the city’s population, but estimates from before the takeover range from 1.2 million to 1.8 million, and estimates for the current population range from 700,000 to 1.5 million. Sunni Arabs made up the majority of the pre-takeover population, and the city is the northernmost outpost of Sunni Arab territory in Iraq. (The lands north of Mosul are predominantly Kurdish.) Even with a Sunni Arab majority, Mosul was a fairly diverse metropolis before the arrival of the Islamic State and contained significant pockets of Shiites and Christians as well as Assyrians, Turkmens and other ethnic groups. Many of these groups have since fled, though pockets of Turkmens and others remain trapped in the city.

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To the north and northeast, Mosul is surrounded by mountainous regions that are controlled by the Kurdistan Regional Government (KRG). To the east, the land is relatively flat until it reaches Erbil, where the mountains begin to rise. To the south, the land is flat. The Tigris flows directly south from Mosul to Baghdad, and the population centers hug the riverbanks before branching out around Baghdad. To the west of Mosul is open desert. Five highways lead into Mosul from all directions, and there are at least four additional roads of varying size and quality that also lead directly into the city. From Mosul, one can reach Syria, Turkey, Iran or Baghdad directly by car. In effect, Mosul is an intersection for the major highways and roads that link most of the region’s major powers.

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This close-up map of Mosul shows where and how IS’ opponents will begin to face real resistance. At the point where the city begins and buildings (rather than open desert) dominate the landscape, the coalition forces’ task will become much more difficult. The Islamic State can set numerous traps for invaders to fall into as they advance block by block and attempt to clear IS from the city. There are also at least five major bridges that span the Tigris and connect various areas of the city. (These bridges are highlighted on the map.) As coalition forces advance, IS can retreat across these bridges and still control at least half of the city.

After advancing fairly easily over open ground in the early phase of the campaign, the coalition forces have now begun facing resistance in towns surrounding Mosul. Invading Mosul itself will be another matter. As illustrated on the map above, the potential for civilian casualties becomes obvious. Each house could contain a family of human shields or unintended casualties; furthermore, the city’s many buildings could be demolished by IS to slow the coalition attack.

The Fragile Coalition

The coalition participating in the invasion of Mosul is made up of fighters from Iraq, mostly the ISF, and the Kurdish peshmerga, with support from the United States. The ISF is nominally in charge, but how that plays out in practice remains to be seen.

The bulk of Iraqi Security Forces are approaching Mosul from the south. The ninth armored division and the first, 15th and 16th army divisions make up a main attack force of approximately 24,000-36,000 soldiers. The peshmerga forces, meanwhile, are approaching from the east and from the north. There are approximately four peshmerga divisions committed to the fight, an estimated 10,000-15,000 fighters (though KRG leader Masoud Barzani has bragged that the number is 30,000).

According to the Iraqi government, the peshmerga will not breach the city of Mosul itself. Rather, the peshmerga’s aim is to close off the north and east to Islamic State fighters. To that end, Iraq’s Counter Terrorism Service (CTS) and special forces are reportedly at the front lines of both the ISF and peshmerga advances. These fighters represent Iraq’s best and have been trained by the U.S. in counter-insurgency tactics. If all goes to plan, they (and not the peshmerga) will be the ones entering the city from the east and north.

The United States is playing an integral role in the coalition’s attack. Without the U.S., there would likely be less productive communication between Kurdish forces and the ISF. Moreover, the CTS is participating in the Kurdish thrusts towards Mosul because the U.S. brokered a deal between Iraq and the KRG that allowed the CTS to be there. There are also at least 100 U.S. joint terminal attack controllers embedded in local units to coordinate airstrikes and artillery strikes in support of coalition movements. According to the Pentagon, both U.S. artillery and Apache helicopters are at the disposal of coalition forces, though the Kurds have already complained that they have not received the level of support they expected. There are also U.S. special forces embedded with the ISF at the division level and with the peshmerga in smaller units, according to the Pentagon.

There are two other groups of forces on the ground that are not officially part of the coalition. These actors are cooperating with the coalition’s advances but they are also pursuing their own interests, which complicates the coalition’s overall mission. The first of these groups consists of an unknown number of Shiite militias, many backed by Iran. Long War Journal has estimated that the total number of both Shiite and Sunni militia fighters is somewhere around 60,000. However, the Shiite militias in particular represent a major challenge to the coalition’s success because there have been numerous allegations of aggressive actions taken by Shiite militias against the Sunni populations they have occupied in neighboring Anbar province and other Sunni-dominated areas. Furthermore, the Sunni Arabs living in Nineveh province (where Mosul is located) are not interested in trading IS dictatorship for sectarian dictatorship.

Iraqi Prime Minister Haider al-Abadi and various Iraqi representatives have insisted that the Shiite militias will not be involved in the main attack on Mosul. Still, according to the Institute for the Study of War, units from the most powerful Shiite militia — the Popular Mobilization Forces — have advanced alongside Iraqi Federal Police units and have filled in areas behind ISF advances. According to Long War Journal, some of these militias will also be involved in a separate attack on Hawija, a pocket of IS territory to the southeast of Mosul.

There is also a small contingent of Turkish ground forces located at a base near Bashiqa; these forces number approximately 450 soldiers and 25 tanks. Turkey has stationed these troops there for over a year, much to the continuing chagrin of the Iraqi government. Both the U.S. and Iraq say Turkey is not a part of the coalition assault on Mosul, but Turkey has defiantly insisted it will be involved if necessary. On Oct. 25, Iran joined this political squabble, insisting that Turkey’s continued violation of Iraqi sovereignty is unacceptable. There are conflicting reports, but it appears that Turkish tanks and artillery have supported the advance of Kurdish peshmerga forces along the Bashiqa axis.

The Islamic State

The Islamic State’s military forces are much harder to parse. The Pentagon says that as recently as July, there were an estimated 10,000 IS fighters in Mosul, but the Pentagon also reports that many top Islamic State officials and their families have left the city. This was contradicted by an Oct. 25 report saying that hundreds of Islamic State fighters were actually pouring into Mosul, arriving via the desert on the western side of the city, to join the fight against the fragile coalition. The most recent estimates of the number of IS fighters in Mosul range anywhere from 2,000-10,000, and in general we tend to err on the side of the upper limit when it comes to gauging IS strength.

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Thus far, the Islamic State has not used much heavy weaponry against the approaching forces. We know from previous reports, however, that IS possesses significant (if limited) firepower. Al-Abadi said last year that Iraq lost 2,300 Humvees to IS fighters in Mosul when the city fell to IS forces in 2014. When things were going well for IS during that same year, the group held a military parade in Mosul and displayed various improvised fighting vehicles, artillery and armored vehicles that it had captured. According to the Pentagon, IS seized 10 M1A1 Abrams tanks as well as ammunition from Ramadi last summer, both of which could have been moved to Mosul. A report from Turkish newspaper the Daily Sabah claimed that the Islamic State has 30 Russian T-55 tanks and five to 10 T-72 tanks, some of which were previously spotted in Mosul.

IS, which has shaky supply lines at best as a result of the coalition’s approach, is likely conserving its ammunition and has thus far opted to both engage in suicide bomb attacks against approaching armor and troops and booby-trap approaches to the city with IEDs. IS has already used crude chemical weapons against U.S. forces in Iraq, and though such weapons are of limited effectiveness, it is suspected IS will continue to attempt to employ them. Additionally, IS is building tunnels in the city and is reinforcing them with concrete walls and barricades. IS is also burning oil and tires to create thick plumes of black smoke that make it harder for artillery to target. Furthermore, they have surrounded the city with oil tankers to block potential coalition advances.

The Islamic State has also resorted to what has become one of its classic tactics: attacking in areas outside the main theater in order to distract enemy forces. On Oct. 21, the Islamic State carried out major small-arms and suicide attacks in Kirkuk, roughly 90 miles southeast of Mosul, killing at least 16. Then, on Oct. 23, IS attacked Rutba, roughly 300 miles southwest of Mosul, and on Oct. 24 attacked Sinjar, a strategically important town on the highway that links Iraq to Syria. While the peshmerga succeeded in fighting off the attack on Sinjar, IS has succeeded in capturing at least half of Rutba, where fighting is still ongoing. Similar attacks will continue, even as the coalition creeps towards the city, although they have not been large enough to divert resources from the attack on Mosul.

The Advance

Now that we understand the battlefield and the major players, we can examine the scope of the battle itself.

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There are currently four main approach vectors for the assault on Mosul. The ISF, led by four brigades of the Iraqi ninth and first divisions, including the 34th armored, have advanced up Highway 80 and reached al-Hamdaniya, roughly 20 miles south of Mosul. Meanwhile, Iraqi CTS and special operations forces, along with peshmerga fighters, have advanced along three axes. The first axis is to the east of Mosul along Highway 2, where forces have reached Bartella, about 10 miles from Mosul. The second is northeast of Mosul, where forces have reached Bashiqa. The third is directly north of the city, where forces are advancing from both Tall Kayf and from Nuran, seizing villages previously controlled by IS along the way.

There are two additional approaches shown on the map above. At least three Iraqi brigades and an unknown number of Iraqi Federal Police forces have advanced to Shura. An unknown number of Popular Mobilization Forces units have also advanced along a parallel line up Highway 1, the only highway leading to Mosul’s west bank. It is unlikely, however, that the Shiite militias or the ISF will continue to approach the city from Highway 1; this approach is dangerous because the highway is met by mountainous terrain before reaching the city, making the approach more difficult than approaches from the east and north. The militias and Iraqi forces are more likely stationed there to protect the flank of the main attack; it is unlikely that they will march on the city.

To date, neither the Iraqi Security Forces nor the peshmerga have reached the city of Mosul proper. However, coalition forces have encountered IS resistance at a number of locations, including Bashiqa, Bartella, Tall Kayf, al-Hamdaniya and Shura, all of which are roughly 10 to 25 miles from the city and are located in relatively sparsely populated areas. Additionally, the coalition has left the west open to tempt IS to retreat from the city rather than fight.

The coalition forces’ strategy will not include a siege; rather, they will attempt to break IS’ will and, failing that, to win a battle of attrition. Either of these options would result in horrific levels of civilian casualties in addition to high casualty rates for the attacking force. Based on current deployments, it appears as if the coalition is opting for the latter strategy, a battle of attrition via attacks from the north and east. It seems as though the coalition aims to drive IS across Mosul’s bridges, to the west bank of the Tigris River. From there, the task of cleaning out IS resistance will become even more difficult because of the potential for a bottleneck at the bridges, and because of the potential for IS to destroy the bridges. Even so, the Iraqi-U.S. coalition does have a significant advantage in terms of numbers of fighters, materiel and air support, and IS cannot hope to win the battle on strength of arms.

The coalition has two major weaknesses. The first is that the coalition’s many disparate parts must continue to play well together. (This includes the various actors that are present but not part of the coalition.) However, there is no guarantee this is possible. Both the Kurds and the Shiite militias have previously shown that they will make opportunistic attacks to secure territory if such a possibility is presented, and they will have ample such opportunities in the battle on Mosul. Additionally, the Turks do not want an Iranian puppet to be in control of Mosul – a city Turkey ruled during the Ottoman Empire – and can claim that their Turkmen brethren require their assistance as well. The Turks thus far have not put enough resources in the field to make a consequential military move, but their presence and political aggressiveness exacerbates already simmering sectarian tensions.

The coalition’s second weakness is that it will be increasingly difficult to maintain the ISF’s morale and composure while leading the attack on Islamic State positions in the city. The Islamic State has had two years to prepare for this attack, and IS will not simply drop its weapons and run when the coalition arrives. Furthermore, the Islamic State must have sympathizers in order to govern such a large city, so many locals are likely to view the invading ISF with a great deal of suspicion. There will be pictures of locals celebrating in the streets at the coalition’s arrival, but there will also be pictures of civilians dying and reports of massive population displacement. Such images and reports will undoubtedly chip away at ISF morale. At the same time, there will be no morale-boosting images of those waiting for the first opportunity to rebel against the Iraqi invaders once they inevitably leave the city.

The Islamic State’s weaknesses are much simpler. IS is outgunned and outmanned. Moreover, opposing forces control all of the major highways and roads into and out of Mosul, so all resupplying has to be undertaken through the desert and is therefore susceptible to U.S. airstrikes. Despite these weaknesses, the IS territory in Mosul is extremely defensible, and IS has proved that its skilled fighting force should not be underestimated. IS fighters are willing to die for their cause, and most of the fighters in Mosul may very well become martyrs, but they wouldn’t engage in this fight if they didn’t think they had a chance of winning. For IS to win the battle, it will need to erode the advance of coalition forces to such an extent that the coalition abandons the approach or devolves into infighting. Considering the complexity of the situation and the coalition’s internal tensions, this is within the realm of possibility.

We do not think IS is going to shrink from this fight; we are also skeptical of reports that say IS has only a few thousand fighters in Mosul and is completely overmatched. Evaluations of IS fighting strength have continually underestimated the group’s abilities. Furthermore, if IS was going to retreat, it would have done so before the coalition forces were arrayed against it and while it could still expect to move through the desert outside Mosul without being the certain target of U.S. air strikes. IS has decided to make a stand here, which means one of two things. IS may think it can fend off the U.S.-backed coalition for long enough to undermine its will to fight. Alternately, IS might think it can inflict such a high cost in the coming battle that all regional actors will pause in attempting a similar feat in Raqqa, IS’ main headquarters, and its stronghold in Deir el-Zour. This reluctance will become all the more pointed as the humanitarian scope of an urban battle in Mosul becomes clear.


A hodgepodge coalition of rivals, former enemies and uneasy allies is marching on the IS stronghold of Mosul. These forces have not yet reached the city, and the battle will not begin in earnest until they do. What lies ahead is a long, difficult and bloody affair. The U.S.-backed ISF and its partners have an overwhelming advantage in terms of fighters and resources, but victory will come at a very high price, one the Islamic State may be able to profit from more than the technical victors. In the meantime, historical rivalries and sectarian divisions – which led to the vacuum that created IS’ rise in the first place – will continue to shape and undermine the fight against IS even once the battle for Mosul has ended.