This NACA High-Speed Flight Station photograph of the Century Series fighters in formation flight was taken in 1957. The F-100 (lower center) had originally been built as a day fighter. The later versions were built as fighter bombers, with some seeing combat in Vietnam. The F-101 (top center) was designed as a long-range escort, but saw service as a fighter bomber, reconnaissance aircraft, and interceptor. The F-102 (right) was designed from the start as an all-weather interceptor, and was used in this role throughout its service life. The F-104 (left) was originally designed as a light-weight fighter, but ended up being used as an interceptor and fighter bomber. These aircraft were flown by the NACA as part of a loan agreement with the Air Force. The NACA learned a great deal from these flights, in return for which NACA research pilots made evaluation flights in support of Air Force development efforts. Such tests were a major NACA activity during the 1950s, and included work on the F-89, F-100, and F-104.