The F-16 "Fighting Falcon" (known as "Viper" to its operators) is a single-engine multirole fighter. It was initially designed and produced by General Dynamics up until 1993 when the company sold the Fort Worth production line to Lockheed Martin. More than 4,500 F-16s have been produced and more than 2,800 aircraft remain in operation with 25 nations, making the type among the most prolific fighter families in the post-World War II period.