The Ling-Temco-Vought A-7 Corsair II is a carrier-based subsonic light attack aircraft introduced to replace the United States Navy's A-4 Skyhawk, initially entering service during the Vietnam War. It was adopted by the United States Air Force and the Air National Guard to replace A-1 Skyraiders, and it was exported to Greece in the 1970s and to Portugal and Thailand in the late 1980s. Its airframe design was based on the successful supersonic F-8 Crusader produced by Chance Vought. It was one of the first combat aircraft to feature a head-up display, an inertial navigation system, and a turbofan engine. Although pilots quipped, "It's not very fast, but it sure is slow," the Corsair performed well in combat. It served as a fighter-bomber and close air support aircraft from 1967 to 1991.