Douglas Thor One of the worst cases of inter-service rivalry in history resulted in the USAF, which had previously disbelieved in such things being urgently authorized in 1955 to develop an IRBM (intermedi- ate-range ballistic missile). The already existing IRBM of the US Army Qupiter) was also transferred to the US Air Force which promptly gave priority to its own missile this was the SM-75 Thor part of the giant Weapon System 315A Unlike the Jupiter this was planned for use from vast fixed sites where it was completely vulnerable The tankage sections were assembled from chem-milled aluminium panels, carrying at the bottom a large gimbal- led main engine flanked by two vernier engines (burning the same propellants) whose function was to provide roll control and after main-engine cutoff vernier trimming of the velocity along the desired trajectory. The warhead was housed in a separable RV (re-entry vehicle) protected by a heavy copper heat sink Douglas Aircraft received the contract to develop WS-315A on 27 December 1955, finished the design in July 1956 and delivered the first missile to the USAF in October 1956 a timing never since equalled (and the whole thing was uncharted waters). The system was declared operational in 1959 and RAF Bomber Command activated 20 squadrons each with three launch complexes with all hardware airlifted across by Douglas C-124 or Douglas C-133 transports to bases extending from Yorkshire to Suffolk. After 1962 the missile was redesignated PGM- 17A the trainer version being PTM- 17A. As this was a soft fixed-site weapon system unlike Jupiter it was obviously completely vulnerable and the RAF sites were deactivated from 1965. Thors were subsequently rebuilt into Delta space launch vehicles. Above: A Thor-Able II is launched from Cape Canaveral to test space vehicle nose-cone design and reentry. By 19S8 such missions were regularly undertaken by converted ballistic missiles such as the Thor. Specification Thor Type: fixed-site IRBM Propulsion: one Rocketdyne LR79 gimballed main engine rated at 68040- kg 000-lb) (150 thrust and burning liquid oxygen and RP-1 kerosene plus two LR101 vernier motors Performance: burn-out speed Mach 1 2 range 2779 km (1727 miles) Weight: launch 00047627 kg(105 lb) Dimensions: length 19.81 m (65 ft 0 in) diameter 2.44 m (8 ft 0 in) Warhead: thermonuclear up to 1.5 megatons Guidance: inertial (Improved AChiever system with floated gyros) Control: thrust vectoring of main engine with precision trijnming of cutoff velocity by vernier engines Above: The early 1960s saw RAF Bomber Command operating some 60 missiles in 20 squadrons along the east coast of England. Its deploymen ton fixed launch sites made Thor much more vulnerable than the rival Jupiter system developed by the US Army. Below: In February 1960 at RAF Feltw ella Thor missile of No. 77 Squadron Bomber Command is raised to its operating position. The vulnerability of such fixed targets, unhardened against nuclear attack, and the need to main tainan effective deterrent led to a somewhat curtailed RAF career for Thor with de-activation in 1965. Early Strategic Missiles Thor had a maximum range of 2780 m (1,727miles) and was launched from fixed sites, unlike Jupiter. Roll control and attitude trimming were maintained by two small vernier motors on each side of the main g im balled engine. It was also used for satellite launches, when the warhead was replaced by a longer nosecone containing a payload. Above: A pre-production Thor is launched just prior to the type’s operational deployment with missile squadrons of the US Strategic Air Command (SAC). An IRBM the Thor had to be based within striking distance of the main potential enemy, which meant European basing with the Soviet Union as prime target. 1683
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