Inside look at U.S.-led coalition's deadliest single attack on ISIL

The initial reports coming into Baghdad’s operations center seemed implausible: A convoy of dozens of Islamic State vehicles were preparing to flee advancing Iraqi forces in Fallujah.

A surveillance drone dispatched to the area confirmed the reports. Staff officers gathered around screens and stared incredulously as the numbers of vehicles continued to expand, the militants apparently oblivious to the target they presented from the air.

It was an unprecedented opportunity. The Islamic State had learned to avoid massing in large numbers to avoid airstrikes by the U.S.-led coalition. Now the militants were clustered in a traffic jam south of the city in what appeared to be a panicked retreat from Fallujah, about 35 miles west of Baghdad. “There was no missing it,” said Maj. Gen. Jay Silveria, deputy commander of U.S. Air Forces Central Command.

When the dust cleared in late June, at least 348 militants were killed and more than 200 vehicles were destroyed, including truck bombs, in one of the deadliest single attacks on the Islamic State since the militants swept into Iraq nearly unopposed two years ago, according to coalition statistics and interviews with officers overseeing the attacks.

“It’s going to change their calculus in the rest of this campaign,” Silveria said, referring to the Islamic State.

The convoy attacks were reported at the time they occurred, but new details that emerged from interviews and military statistics released to USA TODAY highlight an unprecedented effort to capitalize on a quicker than expected ground offensive that took the militants by surprise.

Reports: U.S.-led airstrikes kill at least 250 ISIL fighters near Fallujah

The Islamic State’s deadly miscalculation in Fallujah may be the strongest sign yet that, at least in Iraq, the terror group’s self-proclaimed caliphate is collapsing rapidly.

Over the past weekend, U.S.-backed Iraqi forces captured a key air base that will serve as a staging area for an assault to retake Mosul, Iraq’s second largest city, from the militants. The Pentagon announced Monday it would send an additional 560 U.S. troops to capitalize on the momentum.

Quick Fallujah victory bodes well for Mosul

Two weeks earlier, an estimated 29 coalition aircraft — including B-52s, A-10s, F-15s, F/A-18s, British Typhoons and an armed predator drone — pummeled the Islamic State convoys, dropping more than 70 bombs and missiles over several days.

“It’s an indication of their leadership breaking down,” Silveria said in an interview. “It’s pretty clear they made a poor assessment on the approaching Iraqi security forces and then they made a poor assessment on what it was going to take for them  to get out of there.”

Even when the Islamic State lost ground in other major battles, the militants managed an organized retreat, escaping in small groups and reassembling elsewhere. In Fallujah, however, Iraqi forces caught the militants off guard by moving in to retake the city in about five weeks. By contrast, the recapture of Ramadi, another major Sunni city in western Iraq, took about five months, ending last December.

Even as the Islamic State loses ground and troops, it has proven to be resilient. The group, also called ISIS or ISIL, increasingly is turning to terror attacks against civilians as its grip on territory loosens. In early July, a massive bombing in Baghdad killed about 200 people. In a recent report IHS, a consultant group that tracks the Islamic State, predicted such terror attacks would increase as the Islamic State is pushed out of its territory in Iraq and Syria.

The Pentagon said the shift in Islamic State tactics does not require the U.S. military to overhaul its strategy. “Tightening the noose around ISIL in Iraq will make it harder for them to carry out attacks in places like Baghdad,” Pentagon Press Secretary Peter Cook said.

Plans for the deadly attack in Fallujah began forming when reports of a convoy assembling near a highway intersection south of the city began coming into the joint Iraqi-coalition combat operations center in Baghdad late on the night of June 27. At the time, Iraqi security forces were still clearing pockets of resistance in Fallujah.

Coalition officers scrambled a surveillance drone and began studying the imagery, but they couldn’t positively identify all the vehicles to ensure no civilians were inside.

The next morning, they authorized airstrikes on obvious targets that could be confirmed, including trucks with machine-gun mounts, vehicles rigged with bombs and heavily armored trucks. Some of the pickups had armed fighters piled in the back.

The coalition officers continued to monitor throughout the day, as the convoy grew to more than 120 vehicles, according to an account compiled by Marine Brig. Gen. Rick Uribe, director of the Combined Joint Operations Center-Baghdad, and provided to USA TODAY.

Coalition officers requested “terrain denial” airstrikes — massive craters in roads around the convoy to prevent vehicles from escaping. The mission bought time for officers, as they continued to study the images and identify any vehicles containing civilians.

By 10 p.m. on June 28, the convoy was able to maneuver around the bomb craters and began moving toward an Iraqi military position outside Fallujah. The coalition officers warned the Iraqis that the convoy was headed toward them, but they couldn’t yet order airstrikes because they hadn’t met the strict standards set to avoid civilian casualties.

The military recently moved the authority to approve targets of opportunity, or “dynamic” strikes, to general officers in Iraq, who are closer to the fighting. Previously, approval was granted from U.S. Central Command, headquartered in Tampa, which has overall authority for military operations in the Middle East.

“It’s definitely made a difference in how responsive we are,” Silveria said.

Even so, the process can sometimes be time consuming, since targets of opportunity have to be vetted by teams of officers, including lawyers.

The following day, June 29, one 40-vehicle convoy broke off from the main group and started heading south. By 7:45 a.m., coalition officers positively identified the vehicles as enemy combatants and authorized airstrikes.

The militants had gotten out of the vehicles and were attempting to build bridges to cross a “water obstacle,” according to the military account. It was a prime target. At 8:10 a.m., coalition aircraft started a wave of strikes that wiped out the convoy.

The rest of the convoy was found in the desert heading west at 12:45 p.m. Aircraft began picking off the vehicles individually as soon as they could be identified as legitimate targets.

The convoy was moving toward Iraqi lines even as it was being targeted. Iraqi forces held their ground and repelled the convoy, forcing it to turn around. Coalition aircraft continued attacking the convoy until after 9 p.m., when little was left of it.

That same evening, the coalition began getting reports of another large Islamic State convoy forming in Albu Bali, a village northwest of Fallujah. Coalition officers scrambled a drone overhead and confirmed that more than 120 vehicles were on the move.

Iraqi artillery began targeting the convoy. Coalition aircraft then struck the lead vehicle, which triggered numerous “secondary” explosions, indicating it was rigged as a car bomb, according to the coalition account.

Militants moved another car or truck bomb into the lead position and began moving again about an hour and 15 minutes later. The coalition again hit the lead vehicle, stopping the convoy.

About 50 people, including women and children, fled the vehicles. When the women and children were spotted, the coalition ceased its strikes.

The coalition observed the convoy for about 60 minutes longer to ensure no women or children were around and then destroyed the rest of the column with a series of bombing and strafing runs, according to the coalition account.

Intelligence gathered by the coalition command found the Islamic State concluded that the strikes were a “disaster” for the group, said Air Force Lt. Col. Chris Karns, a military spokesman.

"We were happy to monitor their progress and as they made a mistake we had to take advantage of it," Silveria said.