The Atlas ballistic missile began with the US Army Air Corps request for proposal in October 1945, which led to development in the 1950’s of the Atlas, Navaho, Snark, and Matador/Mace missiles. By January 10, 1946, Consolidated-Vultee’s engineers, under the leadership of Belgian-born Karel Bossart, submitted their proposals for two 6,000-nautical mile missiles: one subsonic, winged, and jet powered; the other supersonic, ballistic, and rocket powered. New technologies proposed for the ballistic missile included extremely low structural weight through use of steel monocoque single-wall construction tanks, kept rigid by internal tank pressure; gimballed rocket engines; detachable payload or warhead section; and nearly single-stage to orbit performance through the ‘stage-and-a-half’ approach of jettisoning the booster engines during the ascent.
     On April 19, Convair received a contract for $1,893,000 to include fabrication and testing of 10 MX-774 Hiroc missiles to verify Bossart’s innovative concepts. Captive testing of the MX-774 research rockets began in San Diego in 1947. In June , Consolidated Vultee was notified that it had lost the cruise missile competition; Northrop and Martin received contracts for development of the subsonic jet-powered designs. History would show that these lead to dead ends whereas the Atlas would be flying at least sixty years later. Defense cutbacks forced the Air Force to terminate the contract in July 1947, only three months before the first scheduled flight. The remaining contract funds did allow three MX-774's to be test-launched at White Sands Proving Ground in July-December 1947. Further work at Convair was reduced to ‘Mafia’ low-level design activity using company funds.
     The outbreak of the Korean war and the beginning of the cold war loosened the federal purse strings. Convair received a new contract (MX-1593) in September 1951 to begin design of a ballistic missile incorporating the design features validated by the MX-774. In 1953 the now-Convair Division of General Dynamics presented a plan to the Air Force for an accelerated program.
    A major propulsion problem in the early 1950's was that liquid rocket motor ignition reliability was less than 50 percent. This led to the stage-and-a-half concept, with all engines ignited prior to lift-off and the booster engines jettisoned during flight. This allowed confirmation that all engines were functioning correctly before releasing the missile for flight.
    A full go-ahead for the Atlas design was ordered in January 1955 as Weapon System WS107A-l. At Convair the project was known the Model 7 (in Russia, Korolev was working on the competing R-7 ICBM - evidently both sides wanted to use the lucky number). In September 1955, faced with intelligence reports of Russian progress on their ICBM, the Atlas received the highest national development priority. The project became one of the largest and most complex production, testing, and construction programs ever undertaken. The first propulsion system and component tests were conducted in June 1956; the first captive and flight-test missiles were completed later the same year.
    The first Atlas A flight took place on June 11, 1957. The first operational missile, the Atlas D, was the basis for launching the Mercury manned spacecraft into orbit. By use of Agena and Centaur upper stages, the Atlas became the medium-lift workhorse of American manned, planetary, and geosynchronous-orbit space programs. Stretched several times, the latest version, the Atlas IIAR, will finally dispense with the booster engine stage in place of two Russian-design rocket engines. Although never copied by other designers, the inflated steel tank approach of the Atlas still gives it the lowest empty weight ratio ever achieved without any reliability penalty.

     After the retirement of the Atlas-Agena in 1978, the Centaur stage became standard on Atlas Launch Vehicles. Lox/LH2 was universally recognized by the space pioneers as the ultimate liquid propellant combination, but use was delayed due to problem of handling the cryogenic liquid hydrogen fuel. NASA's Lewis Research Center (LeRC) did much pioneering work in development of liquid hydrogen technology. LeRC fired the first experimental Lox/LH2 engine of 5,000 pounds thrust in 1953. Centaur itself began with a contract awarded to General Dynamics by the Advanced Research Project Agency in 1958. The first space vehicle to use liquid hydrogen, Centaur was a pioneering project that solved the many technical problems of using the super-cryogenic, explosive, and highly volatile fuel. Pratt & Whitney Aircraft was awarded the contract to develop Centaur's RL-10 engines. The US Air Force built the first large-quantity liquid hydrogen production facility
    In 1962, with the hydrogen propulsion technology being vital to the success of the Apollo program, LeRC was assigned technical management of Centaur. The Centaur project was given the highest DX priority. The first successful flight of Centaur atop Atlas occurred in November 1963. This included the first in-flight ignition of a hydrogen-powered vehicle. However thereafter the Von Braun team’s Saturn S-IV stage, using six of the RL-10 motors, leapfrogged the Surveyor . By the time of the first operational Centaur mission, Surveyor l, in May 1966, the S-IV had already completed its test series of six orbital flights. Yet thirty years later, the Saturn is long gone, and the Centaur continues, having been launched or planned for launch from Atlas, Titan, Delta, and Shuttle vehicles. Production is expected to continue well into the 21st century, and no replacement for the RL-10 engine, the ultimate engine using the ultimate propellants, has been possible.