Two F-35 Lightning II aircraft fly in formation during an aerial refueling training mission, during Operation Astral Knight 19 over the Adriatic Sea, June 3, 2019. Astral Knight is a joint, multinational exercise taking place throughout various locations in Europe, with more than 900 Airmen participating in the exercise. (U.S. Air Force photo by Staff Sgt. Joshua R. M. Dewberry)