McDonnell Douglas is an American aerospace company formed from the 1967 merger of McDonnell Aircraft Corporation and Douglas Aircraft. Both Douglas Aircraft, founded in 1928 by Donal Willie Douglas (1892–1981), and Douglas Aircraft, founded in 1939 by James Smith McDonnell (1899–1980), made important contributions to the US space program. Douglas built the F5D Skylancer prototype used in the development of the Boeing X-20 Dyna-Soar, developed the Thor missile (precursor of the Delta, and built the third stage of the Saturn V. Douglas was chosen to build the Mercury and Gemini spacecraft. Following the merger of the two companies, McDonnell Douglas was contracted to convert of its Saturn V third stages into the Skylab space station. In 1997, McDonnell Douglas merged with Boeing.