The X-planes concept officially came into being in 1944, as a joint programme involving the
National Advisory Committee for Aeronautics (NACA), the
US Navy (USN) and the
US Army Air Forces (USAAF), in order to pursue research into high-speed aircraft. NACA later became the
National Aeronautics and Space Administration (NASA) and the USAAF became the
United States Air Force (USAF). Other organizations such as the
Defense Advanced Research Projects Agency (DARPA) and the
US Marine Corps (USMC) have also since sponsored X-plane projects. The first experimental aircraft specification, for a
transonic rocket plane, was placed in 1945, and the first operational flight of an X-plane took place when the
Bell X-1 made its first powered flight nearly three years later at
Muroc Air Force Base, California, now known as
Edwards Air Force Base. The majority of X-plane testing has since taken place there. X-planes have since accomplished many aviation "firsts" including breaking speed and altitude barriers,
varying wing sweep in flight, implementing exotic alloys and propulsion innovations, and many more. Some of the X-planes have been well publicized, while others, such as the X-16, have been developed in secrecy. The first, the
Bell X-1, became well known in 1947 after it became the first aircraft to break the
sound barrier in level flight. Later X-planes supported important research in a multitude of aerodynamic and technical fields, but only the
North American X-15 rocket plane of the early 1960s achieved comparable fame to that of the X-1. X-planes 8, 9, 11, 12, and 17 were actually
missiles used to test new types of engines, and some other vehicles were unoccupied or UAVs (some were remotely flown, some were partially or fully autonomous). Most X-planes are not expected to go into full-scale production; one exception was the
Lockheed Martin X-35, which competed against the
Boeing X-32 during the
Joint Strike Fighter Program, and has entered production as the
F-35 Lightning II. ==List==