My last post examined Islamic State as a global terrorist entity—a complex and constantly evolving threat. This two-part post focuses more tightly on the unfolding war against ISIS in Iraq. Here things are much clearer: we’re losing.

Anyone reading this already knows much of the history, but to recap: ISIS exploited Iraqi government ineptitude and sectarian division after US forces left in 2011, and used the sanctuary created by the Syrian civil war to grow from an urban guerrilla group—small cells, civilian clothes and vehicles, light weapons, operating mainly by night with asymmetric (i.e. terrorist) hit-and-run tactics—into something more like a conventional light armored cavalry.

By late 2013, when ISIS fighters mounted a major push against the Iraqi cities of Tikrit and Fallujah, their tactical style had settled into a pattern. A main force, often comprising dozens of trucks and troop-carrying technicals, would move in compact formation on highways and secondary roads. Ahead of it, and to the flanks, a swarm of gun trucks—technicals with anti-armor weapons, heavy machine guns, radios and a few dismounts—ranged widely across the landscape, scouting routes, securing chokepoints, and looking for targets of opportunity or soft spots. When they spotted one, they would either “bounce” and overwhelm it with their own resources, or pull the main column onto it using radio and cellphone messages. Teams of two to three technicals, each carrying six or eight fighters ready to dismount, would swarm onto a target, coordinating their fire to overwhelm it. This is classic maneuver warfare—in the business, it’s known as “recon pull”—and it looked a lot like Soviet-style mission tactics, which was unsurprising given the number of Ba’athist officers now on the ISIS payroll.

But there were a couple of variations. First, ISIS columns at this time (we’re talking early 2014 now) operated in much tighter formations than a western armored force would do, clumping together in relatively large columns. They had little to fear from Iraqi air power or artillery: instead of dispersing to protect against these kinds of threats, their formations were optimized for mutual support against a ground-based enemy. Second, unlike conventional troops (or, even, many guerrilla organizations) they made extensive use of suicide bombers, often in improvised armored vehicles, as primitive guided weapons—leading assaults, clearing roadblocks and obstacles, and creating shock effects that could be exploited by the main column to bypass strongpoints or seize defended locations.

Beyond the main force, ISIS maintained a guerrilla capability in and around Iraqi cities, with a network of intelligence sources, safe houses, bomb-makers, snipers and terror cells. These guerrillas fought alongside the main force when it was in their area. But their primary task was harassment, intimidation, reconnaissance, intelligence gathering and propaganda (including information warfare and “propaganda of the deed” killings).

In the first half of 2014, ISIS used these tactics to seize and hold a huge swathe of ground, applying a flexible, mobile defense to defeat Iraqi government counter-attacks. They also captured and put into service increasing numbers of Iraqi armored vehicles including tanks, Bradley fighting vehicles, MRAPs, up-armored Humvees and self-propelled artillery. They also captured numerous heavy and medium towed artillery pieces, mortars and other equipment (mostly of US origin), which was supplemented with Syrian equipment including heavy artillery and Russian-manufactured armored vehicles. This allowed them to create large formations supported by tanks and artillery, making them an extremely formidable adversary. By mid-June, they’d captured Mosul, threatened the outskirts of Baghdad and Ramadi, seized Tikrit and most of Fallujah, and were pushing against the Kurdish capital, Irbil.

This success—which amounted to a conventional blitzkrieg-style offensive across most of western Iraq—prompted the US and its allies (including Australia, Canada and the UK) to intervene with airstrikes in August-September 2014, followed by advisors, trainers and certain special operations capabilities come October. The initial goal was to blunt the ISIS advance, and this succeeded. The Kurdish front stabilized into a form of trench warfare north and west of Irbil, Mosul Dam was recaptured, and Iraqi forces (a combination of demoralized regular troops and increasingly well-armed and assertive Iranian-backed militias known as the “Popular Mobilization”) retook ground around Baghdad, relieving pressure on the capital.

US leaders spoke confidently at this time of rolling back ISIS, rebuilding the Iraqi army, and then recapturing Mosul with the support of international airpower and advisors. In response, ISIS dropped back an evolutionary stage into guerrilla mode. It went back to small teams in civilian clothes, blending into the population and employing night operations and asymmetric attacks. The large formations dispersed into smaller, platoon-sized combat groups, each comprising a few vehicles and 20-40 fighters, and its leaders went underground.

After a few weeks of this, however—and after suffering a few losses—ISIS leaders realized that coalition air activity was going to be relatively easy to handle. Lacking forward ground observers, and operating under highly restrictive rules of engagement, coalition aircraft could only identify and strike a very limited number of targets—on average, from September 2014 to June 2015, the coalition was only able to mount roughly 10-14 strike sorties per day across both Iraq and Syria. (For comparison, during Operation Unified Protector in Libya the daily average was 48; in the invasion of Afghanistan in 2001 the average number was roughly 110; and in the Kosovo campaign of 1999 it was closer to 250.)

In response, ISIS has developed a hybrid approach, which we might characterize as applying “conventional tactics with unconventional means”. The new formation of choice is the platoon plus combat group, comprising 30-40 fighters, a couple of armored vehicles and several technicals, snipers, heavy weapons teams, an artillery piece or two, and backup supplies of ammunition, fuel and water in a supply truck.

Again, that’s a very conventional maneuver approach, but ISIS has supplemented it with very large numbers of IEDs—sometimes emplaced in belts several hundred deep to channel and block attackers—and with suicide bombers in coordinated groups. With a dozen or more of such combat groups working together, but dispersed and maintaining communications so that they could concentrate on targets of opportunity, ISIS could mass substantial force against selected objectives and avoid too serious losses from airstrikes. The number of up-armored suicide bomb trucks was increased, including heavily armored semi-trailers with more than a ton of explosives and armored cabs to protect the drivers as they got as close as possible to their targets. Heavy artillery has been dispersed among the combat groups, and advanced anti-air and anti-armor weapons have made an appearance.

This is the structure—modified slightly through recent fighting—that ISIS is using as it defends its recent gains around Ramadi and pushes against Iraqi forces around the Haditha dam and Bayji oil refinery. The organization’s resilience and success in these battles shows how effective its adaption has been.

In my next post I’ll look at how the Iraqi government and its coalition partners are responding to the evolving military threat posed by ISIS.

This piece first appeared in ASPI's The Strategist here. 

Image: Flickr/U.S. Air Force.