PGM-17 Thor

PGM-17 Thor
Name	PGM-17 Thor
Caption	A Thor missile on its launch pad.
Type	Intermediate-range ballistic missile (IRBM)
Origin	United States
Used by	United States Air Force, Royal Air Force
Designer	Douglas Aircraft Company
Production date	1958–1960
Service	1959–1963 (as missile)
Engine	Rocketdyne LR79 liquid-fuel rocket
Guidance	Inertial navigation system
Launch platform	Launch pad

PGM-17 Thor was the first operational intermediate-range ballistic missile (IRBM) deployed by the United States Air Force. Developed with great urgency during the Cold War, it served as a strategic nuclear deterrent against the Soviet Union and later formed the basis for a highly successful family of space launch vehicles. Its relatively short frontline service as a weapon belied its profound and lasting impact on both military strategy and space exploration.

Development and design

The Thor program was initiated in 1954 as a rapid response to intelligence reports on Soviet missile advances, managed by the Air Force Ballistic Missile Division. The Douglas Aircraft Company was awarded the prime contract, with critical subsystems provided by other major defense contractors: the Rocketdyne LR79 engine (derived from the Navaho missile program), the AC Spark Plug inertial guidance system, and a re-entry vehicle designed by General Electric. The design philosophy emphasized simplicity and speed, resulting in a single-stage, liquid-fueled missile that was transportable by C-124 Globemaster aircraft. Its design was heavily influenced by concurrent work on the SM-65 Atlas, sharing similar construction techniques and propellants, but it was intended for a shorter-range, theater-level role under the operational control of the Strategic Air Command.

Operational history

The first Thor test launch from Cape Canaveral occurred in January 1957 and ended in failure, but a successful flight followed in September of that year. Deployment to the United Kingdom began in 1958 under a dual-key arrangement with the Royal Air Force, with missiles stationed at RAF bases such as RAF Feltwell and RAF North Luffenham. These squadrons, on constant alert, were targeted against key locations within the Warsaw Pact. The height of the Cuban Missile Crisis in 1962 saw Thors brought to their highest state of readiness. However, the missile's volatile liquid fuel and lengthy countdown procedure made it vulnerable, and it was rapidly rendered obsolete by the deployment of more survivable systems like the LGM-30 Minuteman silo-based ICBM and the UGM-27 Polaris submarine-launched missile.

Variants

The basic Thor IRBM served as the foundational core for an extensive family of rockets. The Thor-Able and Thor-Delta combinations were early satellite launchers. The Thor-Agena became a workhorse for launching CIA CORONA reconnaissance satellites and scientific payloads for NASA. Further evolution integrated the Thor with the Douglas-built Delta upper stage, creating the Delta rocket family, which remains in service today. As a first stage, it was also used in the Thorad and Delta II launch vehicles, demonstrating extraordinary longevity and adaptability far beyond its original military purpose.

Specifications (PGM-17A)

The Thor was a single-stage, liquid-propellant missile. It was powered by one Rocketdyne LR79 engine, burning RP-1 kerosene with Liquid oxygen as an oxidizer, producing approximately 150,000 pounds of thrust. The missile was 65 feet in length and 8 feet in diameter. It had an operational range of about 1,500 nautical miles and was designed to carry a Mark 49 thermonuclear warhead with a yield in the megaton range. Guidance was provided by a self-contained inertial navigation system manufactured by AC Spark Plug, a division of General Motors.

Launch sites

Primary testing and development launches were conducted from Cape Canaveral in Florida, at launch complexes such as LC-17. Operational deployment for the Strategic Air Command was exclusively to the United Kingdom, where four RAF bases in East Anglia were modified to host three missiles each on vulnerable above-ground launch pads. These sites included RAF Feltwell, RAF North Luffenham, RAF Hemswell, and RAF Driffield. After retirement as missiles, many Thor cores were repurposed as space launch vehicles, launching from both Cape Canaveral and Vandenberg Space Force Base in California.

Legacy and retirement

The last USAF Thor missiles were withdrawn from the United Kingdom in 1963. Its legacy, however, is monumental. The reliable Thor booster became the most prolific first stage in American space history, forming the cornerstone of the Delta program that launched thousands of satellites, including pioneering missions like Echo 1, Telstar, and Syncom. This transition from a weapon of global thermonuclear war to a pillar of peaceful space access represents one of the most significant conversions of military technology. The Thor directly enabled critical advancements in global communications, weather monitoring, and national security reconnaissance, securing a permanent place in the history of aerospace.

Category:Ballistic missiles of the United States Category:Cold War missiles of the United States Category:Douglas aircraft Category:Rocketdyne engines