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CAMPIA TURZII, Romania — Two American F-15 fighter jets roar down the runway, afterburners glowing, for a near vertical lift-off that pierces through an opening in the clouds.

Moments later, two Romanian MiG-21s follow them for a simulated dogfight over the hilly landscape of Transylvania.

Amid ongoing tensions with Russia, this training session in the former Communist corner of Southeast Europe is part of a wider U.S. military program — Operation Atlantic Resolve — that presents a show of force to potential foes.

“Two of those guys versus two of us came to a merge and there was fighting from there,” said Maj. John. M., one of the F-15 pilots. (The U.S. Air Force asks reporters not to publish his full name for security reasons).

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In addition to the diplomatic standoff between the United States and Russia, concerns have been growing over a massive military exercise planned by Moscow over the next month. With thousands of Russian troops involved, Zapad 2017 could become the country’s largest military exercise since the end of the Cold War.

With American bases drastically reduced across Europe in recent decades, temporary deployments such as the 159th Expeditionary Fighter Squadron's currently stationing at Campia Turzii, Romania, are a way to show both allies and potential enemies that the U.S. military is still active in the region.

U.S. F-15s temporarily stationed at Campia Turzii, Romania. Carlo Angerer

“Operation Atlantic Resolve is our steadfast commitment to support our NATO allies in regional and collective security,” explains Lt. Col. George Downs, the squadron’s commander.

The program has already seen the return of A-10 Thunderbolt II "tankbuster" aircraft to Europe after military officials decided in 2015 that threats from Russia, ISIS, and others throughout Europe and North Africa demanded a renewed presence.

The 159th Expeditionary Fighter Squadron’s roughly 300 airmen and 12 F-15C Eagle fighter jets from the Louisiana and Florida Air National Guards have been running training missions across Europe this summer.

The squadron has taken over part of a hangar at the airfield and set up tents to support the mission, just as they would in a wartime deployment.

“We’re training with our Romanian allies so that we’re better integrated with them in case of future conflict,” Downs says.

The U.S. Air Force stages drills alongside Romanian MiG-21s. Carlo Angerer

“We learn from them and their techniques and tactics, and at the same time, we’re teaching them alongside them with our tactics and techniques, so that we are more integrated with them.”

The training mission also gives U.S. pilots the rare chance to intercept aircraft such as the Romanian MiG-21, a supersonic fighter designed in the former Soviet Union.

“When we’re back home we’re typically used to training against ourselves, we’re always used to seeing F-15s in the air, which is a relatively big fighter,” says Maj. John M. “A MiG-21, which looks different, is quite a bit smaller, always creates a challenge to find them in the sky.”