The SM-65 Atlas was an intercontinental, ground-launched, liquid-fueled, ballistic missile. It was the first ICBM developed and deployed by the United States.

SM-65 Atlas Development

Following the Second World War, the United States sought to produce a ballistic missile able to deliver a nuclear warhead at long ranges. However, due to the weight of nuclear warheads and the fledgling status of the U.S. missile program, it wasn’t until five years later, in 1950, that the U.S. began seriously considering the feasibility of producing such a weapon. First approved in 1951, the Atlas entered the design stage in 1953. Atlas development went through several cycles of cancellation and renewal before it was reclassified by President Eisenhower in September 1955 as the Air Force’s top priority following the recommendation of the Killian Committee and the revelation that the Soviets were working on their own ICBM, the SS-6 Sapwood/R-7 Semyorka.¹

To increase production speed in order to catch up to the Soviets, the Atlas made use of the MA-2 engine system originally produced for the cancelled Navaho cruise missile program. These same engines were also used in the Jupiter, Thor, and Redstone missiles. The Atlas also used a non-standard engine configuration where the three engines were arranged in a straight line (as opposed to a triangular cluster) with the two outer engines functioning as booster rockets which were jettisoned two minutes into the flight.²

The original “Atlas A” variant was first flight tested in June of 1957, but the “D” variant which served as the first U.S. ICBM wasn’t flight tested until April of 1959. The “D” type missile was ordered and entered active service in September 1959.³

Specifications

The Atlas missile had a range of 14,000 km (8,700 miles). It was equipped with the Mk 3 and 4 reentry vehicles and the same 1.44 MT W-49 warhead used on the Jupiter and Thor missiles. The Atlas D model initially used a radio guidance system, but this was later swapped for the same inertial system used on the “E” and “F” models which gave the missile a CEP of 3.7 km. The E and F variants added a self-correcting aspect to the guidance system. The missile was 22.11 m long, 3.05 m wide, and weighed 120,200 kg at launch.⁴

Service History

The Atlas was significant due to its status as the first U.S. ICBM and for its use in the U.S. space program. Through its six-year service period, three variants (D, E, F) of the missile were fielded as ICBMs. As a first-generation ICBM, the missile’s guidance system was not advanced enough to allow for the targeting of hardened facilities, so the missile’s purpose was primarily as a counter value weapon which could destroy ports, and cities.⁵

The initial “D” variant was first fielded using a gantry-style launch pad. However, the gantry storage made it difficult for maintenance crews to service and left the missiles exposed to the elements. In order to offset these issues, the Air Force began housing the missiles in above-ground “coffin” bunkers where the missiles were stored horizontally when not in use. When a missile was ready to launch, the roof of the bunker would slide open and a hydraulic lift would raise the missile 90 degrees into the firing position. The “D” variant was capable of firing within 15 minutes of receiving a launch command.⁶

The “E” variant entered service in September 1961 and introduced an inertial guidance system adapted from the Snark intercontinental cruise missile to replace the radio controlled one and, in order to increase survivability of the missile in event of an attack, the coffin bunkers housing the “E” type were built into the ground.⁷

The “F” model was first fielded in September 1962 and was the first missile to implement the underground, upright silo storage method, still in use today. This change came about due to improvements in missile guidance systems which could potentially threaten the safety of coffin bunkers. The new silos were built to resist overpressure of up to 100 psi, making the Atlas invulnerable to all but a direct hit. Additionally, the “F” type was able to fire within 10 minutes of receiving a launch order because it was stored vertically and did not need to be lifted into a firing position.⁸

Space Launch Applications

Atlas was also used, starting in 1962, by the National Aeronautics and Space Administration (NASA) as the primary launch vehicle for the Mercury space program. Under the Mercury program, the missile was used in nine flights, four of which were manned (Mercury 6, 7, 8, 9). John Glenn’s Mercury 6 mission was the third American manned space flight. He was proceeded by Alan Shepard and Gus Grissom who flew using modified Redstone missiles.⁹

Following its success in the Mercury program, the Atlas saw use as a heavy cargo rocket for the Gemini space program, launching the Agena Target Vehicles used by the Gemini astronauts to practice orbital docking for the later Apollo missions. Additionally, the missile was used for the Atlas-Centaur launch vehicle series, a series of space lifters which were used for commercial satellite launches until 2004.¹⁰