The Rockwell XFV-12 was a prototype supersonic United States Navy fighter which was built in 1977. The XFV-12 design attempted to combine the Mach 2 speed and AIM-7 Sparrow armament of the McDonnell Douglas F-4 Phantom II in a VTOL (vertical takeoff and landing) fighter for the small Sea Control Ship which was under study at the time. On paper, it looked superior to the subsonic Hawker Siddeley Harrier attack fighter. However it was unable to demonstrate an untethered vertical takeoff and its inability to meet performance requirements terminated the program.