The 21st Fighter Squadron is part of the 56th Operations Group at Luke Air Force Base, Arizona. It is a United States Air Force squadron that operates Taiwanese-owned General Dynamics F-16 Fighting Falcon aircraft conducting fighter and maintenance training for the pilots and maintainers of the Republic of China Air Force. Prior to reforming at Luke in 1997, the 21st Tactical Fighter Training Squadron operated McDonnell F-4E Phantom IIs at George Air Force Base, California until 1993.