In early June, the U.S. Air Force conducted air and missile defense drills alongside multiple allies at Aviano Air Base in Italy and other locations in Europe. Known as Astral Knight 2019, the exercise integrated airmen, soldiers, and sailors from the United States, Croatia, Italy, and Slovenia to train and test allied interoperability. Terminal High Altitude Area Defense (THAAD) and Patriot missile defense systems were incorporated in the exercise, as well as over 30 USAF aircraft including F-16s and F-35s. Operating out of various bases, B-52 Stratofortress, KC-135 Stratotanker, E-3 Sentry, and MiG-21 aircraft also participated in the exercise.