The Ling-Temco-Vought A-7 Corsair II was a carrier-capable subsonic light attack aircraft introduced to replace the Douglas A-4 Skyhawk. The A-7 airframe design was based on the successful supersonic Vought F-8 Crusader. It was one of the first combat aircraft to feature a head-up display (HUD), an inertial navigation system (INS), and a turbofan engine. The Corsair II initially entered service with the United States Navy during the Vietnam War.