Design work on the C-133 began when the United States Air Force issued a requirement in the early 1950s for a new strategic airlifter. No prototypes were built, with the aircraft instead going straight into production as the C-133A. It first flew on April 23rd, 1956 and entered service in August 1957 with the Military Air Transport Service. 50 Cargomasters were built between the aircraft's two variants (C-133A and C-133B). They were used to transport ICBMs and rockets for the NASA's space program, and saw service during the Vietnam War. At the time of its introduction, the C-133 was the largest transporter America had, but it was soon outclassed by the C-141 Starlifter and C-5 Galaxy. Due to this, and the aircraft deteriorating in condition, all were retired by 1971.