The Cargomasters went directly into production as C-133A; no prototypes were built. The first Cargomaster flew on 23 April 1956. The first C-133As were delivered to the Military Air Transport Service (MATS) in August 1957 and began flying MATS air routes throughout the world. Two C-133s established transatlantic speed records for transport aircraft on their first flights to Europe. The fleet of 50 aircraft proved itself invaluable during the Vietnam War. The Cargomaster soldiered on until the Lockheed C-5 Galaxy entered service in the early 1970s. The C-133 was then retired and most airplanes were cut up within months of being delivered to Davis-Monthan Air Force Base, Tucson, Arizona, after their final flights in 1971.