The United States and Bulgaria will conduct joint air patrols for the first time under the NATO aegis, a new (albeit relatively mild) show of force by Washington in the Black Sea region.

The patrols will take place in mid-September, with two American F-15s patrolling alongside Bulgarian MiG-29s. “NATO takes its responsibility to ensure the safety and integrity of our airspace very seriously. This mission is a demonstration of solidarity and support for our ally Bulgaria,” NATO Deputy Secretary General Alexander Vershbow said in a statement.

Recall that earlier this month Russia deployed S-400 air defense systems to Crimea in order to deter what some Russian officials called NATO's "air hooligans." That, in turn, followed a statement made at NATO's July summit in NATO that it would implement "appropriate measures, tailored to the Black Sea region" and that "options for a strengthened NATO air and maritime presence will be assessed."

And just last week, Russian air, sea, and land forces took part in snap drills around the Black and Caspian seas, which focused on air defense.

That said, this appears to just be around Bulgaria's air space, not the Black Sea per se. But it's still sensitive, including in Bulgaria: the Wall Street Journal reported that "Bulgaria pulled out of a plan for joint alliance patrols in the Black Sea earlier this year, and the head of the Bulgarian air force resigned this month protesting the possibility of joint air policing with the U.S."

The U.S. deployment is likely aimed primarily at a Bulgarian audience, said Michael Kofman, a military analyst at CNA Corporation and a fellow at the Wilson Center’s Kennan Institute. Countries on NATO's southeastern flank see how focused NATO is on boosting its presence around the Baltic region. "It's about pleasing NATO countries who compete with each other for attention," he said, "so Bulgaria doesn't feel left out."