 In addition to active duty in the U.S. Air Force, Air Force Reserve Command, and Air National Guard units, the aircraft is also used by the USAF aerial demonstration team, the U.S. Air Force Thunderbirds, and as an adversary/aggressor aircraft by the United States Navy.The F-16 has also been procured to serve in the air forces of 25 other nations.As of 2015, it is the world's most numerous fixed-wing aircraft in military service.