The museum's C-133 was the last of the 50 C-133s to be manufactured. Designed around the major mission of hauling the first generation of intercontinental ballistic missiles, including the Atlas missile, the C-133 used an aft loading ramp, clamshell doors, and a large circular fuselage to make loading much easier than earlier cargo planes. It remains the largest turboprop aircraft ever built for the U.S. Air Force. In 1958, a Dover AFB C-133 broke the world's heavy-lift record by 40,000 pounds when it lifted 117,900 pounds to 10,000 feet. Besides missiles, it could carry 16 loaded jeeps or three fire trucks in its cavernous cargo compartment, and it could haul 96 percent of the vehicles in the U.S. Army's inventory. The 463L pallet system still used on current U.S. Air Force aircraft was first tested and used operationally on the C-133. Only 50 Cargomasters were built, with Dover and Travis serving as home bases until the last C-133 was retired in 1971.