The U.S.-led air campaign against the Islamic State in Iraq and Syria often prioritized tactical, close-air support operations and bombing runs over strategic, "deep strike" missions, according to a new Rand Corp. report.
But while the aggressive effort crippled some ISIS strongholds, it did little to accelerate the caliphate's defeat in the long run, the report found.
In "The Air War Against the Islamic State: The Role of Airpower in Operation Inherent Resolve," researchers conclude that territory-limiting operations were seen as the measure of success during the escalated effort, which ran from 2014 to 2019.
"Deep-strike operations helped stress ISIS's finances and hasten its demise but were ultimately peripheral to the overall strategy," according to the study, published Friday. "Because eliminating ISIS's protostate was paramount, territory was the key measure of success in OIR, which in turn meant that the close fight was prioritized over the deep fight."
The 500-page study used open-source data and reporting as well as interviews with officials.
The conflict was complex, waged in two countries with different authorities and rules of engagement for U.S. and coalition partners. As a result, the majority of U.S. military support came from airpower, the report states.
The report breaks the effort into three phases: degrade (2014-15), counterattack (2016-17) and defeat (2018-19), and focuses on offensive campaigns devoted to key geographic locations and timelines. For example, it breaks out how increased B-1B Lancer bomber and fighter sorties were dedicated to driving ISIS fighters out of Kobani, Syria, during the final four months of 2014.
In a comparison of U.S.-led military interventions in recent decades, the air campaign against ISIS is second only to the 1990-91 Operation Desert Storm in terms of weapons dropped: 115,983 to 227,000, according to the report, though the anti-ISIS effort has run for much longer.
The study did not look at other regions, such as Libya and Afghanistan, which have seen offshoots of ISIS fighter groups.
Using air power to support local partners' ground forces was the primary strategy to reclaim territory, especially during the first two years of the campaign, the report found.
"Because the United States wanted a 'limited liability, limited risk' approach that also produced an enduring outcome, the United States identified Iraqi and Syrian partner ground force operations as the primary effort," it states. "This in turn meant that [close-air support, or CAS] was prioritized over strategic attack operations."
Rand notes a longstanding debate between ground force commanders and air power theorists on the use of CAS versus strategic strikes.
CAS actions, conducted via attack aircraft such as the A-10 Warthog, aim to cut off the enemy's ability to maneuver.
But air power advocates "argue that air forces are most strategically effective when their capabilities are used in strategic strikes against an enemy's centers of gravity -- that is, high-value targets that produce disproportionate effects against an adversary's military or political will to fight," the report states, adding that, while CAS is essential in any ground-heavy war, its effects "are localized and tactical."
The researchers point out that CAS alone wasn't enough.
MQ-1 Predator and MQ-9 Reaper intelligence, surveillance and reconnaissance, or ISR, aircraft were needed to conduct overwatch for ground forces prior to and during a ground assault. They were also indispensable for deliberate targets, or those that required weeks of scrutiny and planning. As a result, the drones were overtasked.
Refueling tankers were also in demand, loitering for hours to provide gas to aircraft engaging forces below. "None of these operations would have been possible without tankers that refueled joint and coalition partner aircraft," the report says.
Slow Target Approval
Even with the increased pace of air operations, it was difficult to examine air power's effects during the earliest months of the war "because of the intelligence problems that impeded the development of deliberate targets," according to the report. Those targets included ISIS safe havens where the group centralized cash reserves and sources of revenue, such as oil facilities.
Critics argue that Operation Inherent Resolve was also hindered by "an excessive focus on the avoidance of collateral damage and casualties."
ISIS fighters recognized this and quickly began to modify their behavior, making it harder for U.S. and coalition forces to distinguish them from civilians, according to the report.
After that, targeting time lagged: U.S. pilots reported that the approval process for dynamic targets -- those that weren't defined during a mission's planning stages or sought out ahead of time -- routinely took "more than 30 minutes and sometimes even lasted hours" before they could strike, the report states.
"Anecdotally, we often heard that Iraqi ground forces were frustrated by the slow target-approval process and wanted coalition air strikes to be more responsive to their needs," said the researchers, adding that the views of the government of Iraq, Syrian partners and other coalition members "might have been different."
The airspace over Syria became even more contested as Russia entered the battlespace in 2015, along with Iranian-made drones.
The pace accelerated when target engagement authority was delegated to lower echelons. In 2017, then-Defense Secretary Jim Mattis credited President Donald Trump for that decision.
"[Trump] delegated authority to the right level to aggressively and in a timely manner move against enemy vulnerabilities," Mattis told reporters during a briefing at the time.
While this was most effective against small, mobile targets, the results "improved battlefield outcomes," according to the report.
Another problem, according to the report, was that pilots were reluctant to engage forces other than ISIS given the U.S.' limited intervention strategy and had to be reminded they could take actions in self-defense.
Then-Lt. Gen. Jeffrey Harrigian, the Combined Force Air Component Commander, had "to empower airmen and remind them that they were not only supported but required to execute this defensive mission."
In June 2017, an F/A-18E Super Hornet conducted the U.S. military's first air-to-air kill involving a manned aircraft in nearly two decades when it downed a Syrian Su-22 Fitter south of Taqbah. That same month, F-15Es shot down two armed pro-Syrian regime Shaheed-129 drones.
Lessons for the Future
The report recommends that troops brush up on "atrophied" skills, including coordinated intelligence gathering and targeting. There were many shortcomings in the deliberate target-development process, researchers said, due to a shortage of drones and lack of guidance from proper chain-of-command channels.
Combined Joint Task Force-Operation Inherent Resolve, the U.S.-led international coalition, was under-resourced to execute both the tactical fight and the joint targeting process, the researchers found.
"After decades of flying primarily overwatch mission with little but CAS and dynamic targets since September 11, the joint community's ability and capacity to plan and develop a deliberate
strike operation in the deep areas atrophied," they wrote.
This also affected the Combined Air Operations Center at Al Udeid Air Base, Qatar, where airmen had "to build a target set from scratch."
"This meant that many practitioners lacked experience in applying these processes to real-world operations and the 'muscle memory' to rapidly execute them," according to the report.
The researchers also emphasized that pilots took defensive counterair more seriously only after they were empowered to do so. In order to better prepare airmen for a potential near-peer conflict, self-defense rules of engagement in air-to-air operations "should be stressed" before the mission begins, they wrote.