The Joint Strike Fighter (JSF) became synomous with the later F-35 Lightning II, however until 2001 the term was applied to the competition between the Boeing X-32 and Lockheed Martin X-35. The JSF program was designed to replace the F-16, A-10, F/A-18 and AV-8B fleet of tactical fighter aircraft in U.S. military service.The F-35 Lightning II—descended from the X-35 of the Joint Strike Fighter (JSF) program—is a single-seat, single-engined military strike fighter, a multi-role aircraft that can perform close air support, tactical bombing, and air-to-air combat. Its development is being funded by the United States, the United Kingdom, and other partner governments. It is being designed and built by an aerospace industry team led by Lockheed Martin and major partners BAE Systems and Northrop Grumman. Demonstrator aircraft flew in 2000 a production model first took flight on 15 December 2006.The F-35 appears to be a smaller, slightly more conventional, one-engine sibling of the sleeker, two-engine F-22 Raptor, and indeed, drew elements from it. The exhaust duct design was inspired by the General Dynamics Model 200, a 1972 VTOL aircraft designed for the Sea Control Ship.Lockheed teamed with the Yakovlev Design Bureau in the 1990s, which has led to some speculation about ties with the quite different Yakovlev Yak-141 'Freestyle'