From the Wright Brothers’ first successful flight in 1903, early American aviation was initially unregulated. In 1915, the National Advisory Committee on Aeronautics was established to promote and coordinate research and development in the field. US involvement in World War I stimulated aviation manufacturing and technology. In 1918, the Post Office was contracted to provide the first Airmail Service, initially between New York and Washington, but in 1920, a transcontinental service with 13 stops was introduced. The 1926 Air Commerce Act enshrined federal oversight of aviation, with the Department of Commerce now responsible for the licensing of pilots, the operation and maintenance of navigational aids and the issuing and enforcement of air traffic rules. By 1930, a substantive scheduled flight network existed countrywide. In 1934, safety and accident investigation was hived off from air traffic control, and in 1940 sequestered in a separate federal agency, the Civil Aeronautics Board.