The U.S. Air Force is deploying to Turkey up to a dozen jet fighters specializing in air-to-air combat—apparently to help protect other U.S. and allied jets from Russia’s own warplanes flying over Syria.

Officially, the deployment of F-15C Eagle twin-engine fighters to Incirlik, Turkey—which the Pentagon announced late last week—is meant to “ensure the safety” of America’s NATO allies, Laura Seal, a Defense Department spokesperson, told The Daily Beast.

That could mean that the single-seat F-15s and the eight air-to-air missiles they routinely carry will help the Turkish air force patrol Turkey’s border with Syria, intercepting Syrian planes and helicopters that periodically stray into Turkish territory.

But more likely, the F-15s will be escorting attack planes and bombers as they strike ISIS militants in close proximity to Syrian regime forces and the Russian warplanes that, since early October, have bombed ISIS and U.S.-backed rebels fighting the Syrian troops.

Seal declined to discuss the deployment in detail, but hinted at its true purpose. “I didn’t say it wasn’t about Russia,” she said.

Russia’s air wing in western Syria is notable for including several Su-30 fighters that are primarily air-to-air fighters. The Su-30s’ arrival in Syria raised eyebrows, as Moscow insists its forces are only fighting ISIS, but ISIS has no aircraft of its own for the Su-30s to engage.

The F-15s the U.S. Air Force is sending to Turkey will be the first American warplanes in the region that are strictly aerial fighters. The other fighters, attack planes and bombers the Pentagon has deployed—including F-22s, F-16s, A-10s and B-1s—carry bombs and air-to-ground missiles and have focused on striking militants on the ground.

In stark contrast, the F-15s only carry air-to-air weaponry, and their pilots train exclusively for shooting down enemy warplanes. It’s worth noting that F-15Cs have never deployed to Afghanistan, nor did they participate in the U.S.-led occupation of Iraq. The war in Syria is different.

The dogfighters are part of a broader escalation of the air war over Syria. In addition to jets in Jordan, Kuwait, and the United Arab Emirates, and Navy and Marine planes aboard aircraft carriers, the U.S. Air Force recently added A-10 attack jets and rescue planes and helicopters at Incirlik in Turkey.

Incirlik and its growing contingent of warplanes is the key to a new northern strategy in the U.S. campaign against ISIS, an unnamed Pentagon official said on Oct. 30. “One of the principal things we will do to put pressure in the border area and into Syria is, quote, ‘thicken’ air operations in northern Syria.”

“That means we want a greater density of planes striking. We need a greater density of intelligence assets developing targets. You—the White House announced A-10s, which are already on the ground at Incirlik, and F-15s forthcoming on—in Incirlik, to help in the counter-ISIL campaign,” the official added, using another acronym for ISIS.

But the Pentagon has not said it will enforce a no-fly zone over northern Syria in order to protect pro-U.S. rebels from Syrian—and Russian—warplanes. “It is something obviously, you know has been in the conversation, and has been in the discussion, but today’s announcements are not keyed any way to the beginning or start of a no-fly zone,” the unnamed official said

Such a zone could compel F-15s and other U.S. planes to directly confront Russian planes, even though—in theory—both air forces are attacking ISIS. Russia and the United States do make efforts to steer their jets away away from possible collisions, but otherwise do not collaborate in their separate air wars in Syria.

Instead, American and Russian pilots and air controllers keep wary eyes on each other as they conduct independent and occasionally conflicting bombing raids. “They are keenly aware of what happens, as we are, over the skies of Syria, and coming in and out of Syria,” the Pentagon official said of Moscow’s military planners.

And now the United States will have fighter jets in Syria whose main job could be to watch out for Russians.