According to the Pentagon , the incident began after approximately 500 troops allied with Syrian dictator Bashar Al Assad crossed to the eastern side of the Euphrates River near the city of Deir ez-Zor with tanks, artillery, and other heavy weapons on Feb. 7, 2018. That force passed over a formal de-confliction line that the United States and Russia have set up to try and separate their activities and avoid these skirmishes. It subsequently used tanks or artillery to fire at least 30 rounds at a headquarters run by the Syrian Democratic Forces (SDF), a U.S.-backed local force, the bulk of which are Kurds . American advisers, likely special operations forces, were also at the site and subsequently called in a flurry of air and artillery strikes.

The U.S. military has now offered additional details about the withering firepower it employed during a three hour battle to beat back a battalion-sized force that threatened American troops and their local partners at a remote base in northern Syria . Coming as the United States is trying to draw down in Iraq and Syria and shift its attention to Afghanistan , the incident underscores how difficult it might be for the remaining U.S. troops to not to get wrapped up in the broader Syrian conflict .

“F-22A Raptors and MQ-9B Reapers, were overhead providing protective overwatch, defensive counter air and [intelligence, surveillance and reconnaissance] support as they have 24/7 throughout the fight to defeat ISIS,” U.S. Air Force Lieutenant Colonel Damien Pickart, a spokesman for Air Forces Central Command, told Military.com in a statement. “Following a call for support from Air Force Joint Terminal Attack Controllers, a variety of joint aircraft and ground-based artillery responded in defense of our SDF partners, including F-15E Strike Eagles.”

It’s not the first time any of these assets have taken part in operations in Syria. It’s also not the first time American aircraft have discouraged forces aligned with Assad’s regime in Damascus from approaching SDF positions or outright attacked them. But the size and scope of the response underscores both the apparent severity of the threat and that the United States has no choice but to remain heavily committed to operations in Syria if it wants to continue having a meaningful presence in the country.

As Colonel Pickart noted, F-22s and MQ-9s have become an increasingly common sight over SDF-controlled areas in Syria for years, keeping watch for threats in the air and on the ground. In 2015, Russia released footage of one of its Su-30 Flanker-C fighter jets flying near a Reaper drone somewhere in Syria.

Then, in August 2016, Raptors swooped in to chase off Syrian combat aircraft in northern Syria that appeared to be setting up to attack U.S.-backed fighters and their special operations forces advisers. A U.S. Navy F/A-18E Super Hornet actually short down a Syrian Arab Air Force Su-22 Fitter jet in June 2017. More recently, in December 2017, one of the stealth fighters nearly collided with a Russian Su-25 Frogfoot ground attack aircraft during a contentious engagement along the Euphrates River.

It’s not clear if either of these types of aircraft conducted actual strikes against the pro-Assad forces or simply monitored their activities and kept a guard up in case Syria’s Air Force attempted to intervene. The F-15E Strike Eagles, which can carry much more larger payloads than either the F-22 or the MQ-9, were likely more significant contributors in the hours-long fight. In a series of incidents in 2017, F-15Es similarly raced to aid of American special operators and their local partners in the Southern Syrian city of At Tanf, attacking columns of Iranian-backed militiamen in armored and other vehicles, as well as shooting down two Iranian-made drones.