The 11 days of drills are set to take place amid heightened tensions with Russia as the Ukraine war escalates.

The Air Defender 23 drill will take place from June 12-23 and will see 10,000 participants and 250 aircraft from 25 nations train, in order to respond to a simulated attack on a NATO member country.

“This is an exercise that would be absolutely impressive to anybody who’s watching, and we don’t make anybody watch it,” United States Ambassador to Germany Amy Gutmann told reporters in Berlin, highlighting that an audience could include Russian President Vladimir Putin.

“It will demonstrate beyond a shadow of a doubt the agility and the swiftness of our allied force in NATO as a first responder,” she added.

While the drill had been planned for years, Russia’s invasion of Ukraine in February last year has jolted NATO members, and efforts to expand and fortify the military alliance have increased.

Sweden, which seeks to become a NATO member, and Japan will also take part in the drill.

“We are showing that NATO territory is our red line, that we are prepared to defend every centimetre of this territory,” said Lieutenant General Ingo Gerhartz of the German Air Force, which is coordinating the exercise. “But we won’t, for example, conduct any flights toward Kaliningrad. So this is intended to be defensive.”

Kaliningrad is a Russian exclave located on the Baltic Sea between Poland and Lithuania.

Lieutenant General Michael A Loh, director of the US Air National Guard, said the exercise goes beyond deterrence.

“It’s about the readiness of our force. It’s about coordination, not just within NATO, but with our other allies and partners outside of NATO,” he said.

Three air exercise areas will be used for two to four hours a day, according to Germany’s air command.

But for safety reasons, they say that the airspace for civilian airlines will be closed during these time windows, which could in turn disrupt some passenger flights to and across Europe.