Early USAF Missile Evolution: Atlas, Thor, Titan, and Minuteman Launchers

Artist’s cponception of an Atlas hardened ICBM silo.

During the early 1950s all the armed services of the United States worked toward the fielding of ballistic missiles that could deliver warheads to enemy targets, in some cases intercontinental targets half a world away. Competition was keen among the services for a mission in the new “high ground” of space, whose military importance was not lost on the leaders of the world.

In April 1946 the Army Air Forces gave Consolidated Vultee Aircraft (Convair) Division a study contract for an ICBM. This led directly to the development of a succession of ballistic missiles in the 1950s. This was a revolutionary effort that gave humanity for the first time in its history the ability to attack one continent from another. And there was no effective defense. It shrank the size of the globe, and the United States—which had always before been protected from outside attack by two massive oceans—could no longer rely on natural defensive boundaries or distance from its enemies. In the space of Eisenhower’s two terms as president, therefore, the United States moved from a position of having essentially no space access to possessing ICBMs with a significant capability.

The Air Force entered the race to build long-range ballistic missiles with dramatic flair during 1954, receiving formal approval for the rapid development of three major liquid-fueled weapons—Atlas, Titan, and Thor. The Atlas was the first of these. It received high priority from the White House and hard-driving management from Brigadier General Bernard A. Schriever (1900-2005), a flamboyant and intense Air Force leader. Known as the SM-65 Atlas program, it initially went by the name “Weapon System 107A,” this work officially began in February 1954. The first Atlas rocket was test fired on June 11, 1955, and a later generation rocket became operational in 1959. These systems were followed in quick succession by the Titan ICBM and the Thor intermediate-range ballistic missile. By the latter 1950s, therefore, rocket technology had developed sufficiently for the creation of a viable ballistic missile capability.

At first many engineers believed Atlas to be a high-risk proposition. To limit its weight, Convair Corp. engineers under the direction of Karel J. Bossart (1904-1975), a pre-World War II immigrant from Belgium, designed the booster with a very thin, internally pressurized fuselage instead of massive struts and a thick metal skin. The “steel balloon,” as it was sometimes called, employed engineering techniques that ran counter to the conservative engineering approach used by Wernher von Braun and his “Rocket Team” at Huntsville, Alabama, working at the Army’s Redstone Arsenal. Von Braun, according to Bossart, needlessly designed his boosters like “bridges,” to withstand any possible shock. For his part, von Braun thought the Atlas was too flimsy to hold up during launch. The reservations began to melt away, however, when Bossart’s team pressurized one of the boosters and dared one of von Braun’s engineers to knock a hole in it with a sledge hammer. The blow left the booster unharmed, but the recoil from the hammer nearly clubbed the engineer.

A second ballistic missile, Thor, dates from January 1956 when the Air Force began developing it as a 1,500 mile intermediate-range ballistic missile (IRBM). The Thor program progressed rapidly under contract to the Douglas Aircraft Corp., and the first flight of the Thor IRBM took place on January 25, 1957. In August 1958 the USAF’s first operational squadron entered service in Europe. The Thor was a stop-gap measure, however, and once the first generation of ICBMs based in the United States became operational, the Thor missiles were quickly retired. The last of the missiles was withdrawn from operational alert in 1963. With modification and the addition of an upper stage, it remained a workhorse in America’s fleet of launchers under the name Thor-Delta (later as Delta), propelling moderate payloads into orbit until the twenty-first century. It launched, among other payloads, the first CORONA satellite reconnaissance spacecraft into orbit beginning in 1960.

The Titan ICBM program emerged not long after Atlas, and proved to be an enormously important ICBM effort and later a civil and military space launch asset. To consolidate ballistic missile development efforts, Secretary of Defense Charles E. Wilson (1886-1972) issued a decision on November 26, 1956, that effectively took the Army out of the ICBM business and assigned responsibility for land-based systems to the Air Force and sea-launched missiles to the Navy. The Air Force began what became the Titan family of boosters in October 1955 by awarding the Glenn L. Martin Company a contract to build an intercontinental ballistic missile (ICBM). This missile had been ordered as a backup to the Atlas ICBM then in development—the Air Force had some nagging doubts about some of the technology being incorporated into Atlas.

This new missile became known as the Titan I, the nation’s first two-stage ICBM. Designed to be based in underground silos, USAF deployed 54 Titan Is followed by 54 improved Titan IIs. The first Titan II ICBMs were activated in 1962, and modified Titan IIs were selected to launch NASA’s Gemini spacecraft into orbit during the mid-1960s. As a result of arms and nuclear reduction treaties, the Titan II weapon system was deactivated during the mid-1980s, with the missiles being removed and the silos destroyed. As a result of this decommissioning, several of the old Titan II ICBMs found use as space launchers in the post-Challenger era of commercial space operations in the 1990s.

While Atlas, Thor, and Titan were important steps forward in ballistic missile capability, their liquid-fuel propulsion system took too much time to prepare for launch. A solution was a solid-propellant system that obviated the need for constant servicing. Hence, the silo-based, three-stage Minuteman became America’s workhorse ICBM during the bulk of the Cold War.

The Minuteman Missile National Historic Site, South Dakota.

Approved for development in September 1958, USAF put on alert its first ten Minutemans (LGM-30A/B) at Malmstrom Air Force Base, Montana, in October 1962. This Minuteman I, which had a single nuclear warhead, was superseded by Minuteman II and III missiles that could carry up to three independently targeted nuclear warheads. In all 550 Minuteman IIIs were deployed in the United States beginning in 1970. This ICBM remains on alert, a total of 500 single reentry vehicle Minuteman IIIs serving as the nation’s ICBM deterrent through 2020.