Commercial air passenger service began in the United States (and in the world) in 1914, with a regularly scheduled flight that carried passengers between St. Petersburg and Tampa, Fla. However, there was little demand for commercial aviation and it developed slowly until after World War II. Most of the development in the aeronautical industry prior to World War II happened in the military sphere and was overseen by the National Advisory Committee on Aeronautics (NACA), which was established by Congress in 1915. The period between the two World Wars was a time for improvements in airfoils, propellers, engines, and instruments and innovations in construction techniques and materials.
To regulate the aeronautic industry, the U.S. Congress passed the Air Commerce Act of 1926, which created a Bureau of Aeronautics within the Commerce Department. The bureau moderated commercial airlines, licensed pilots, and certified aircraft. Further regulation of passenger safety, route markings, and air traffic control was provided by the Civil Aeronautics Act of 1938 and the Civil Aeronautics Board and Civil Aeronautics Administration Act (1940).