PGM - 17 Thor Thor was the first operational ballistic missile in the arsenal of the United States , operated by the US Air Force . Thor was in height and in diameter . Named after the Norse god of Thunder , it was deployed in the UK between 1959 and September 1963 as an Intermediate Range Ballistic Missile ( IRBM ) with thermonuclear warheads . It was later augmented in the U . S . IRBM arsenal by the Jupiter . A large family of space launch vehicles — the Delta rockets — were derived from the Thor design . A modified version is still in use today as the first stage of the Delta II . Design and development . Fearful that the Soviet Union would deploy a long - range ballistic missile before the United States , in January 1956 the Air Force began developing the Thor , a intermediate - range ballistic missile ( IRBM ) . The Thor program unfolded with amazing speed , and within 3 years of the program ’ s inception the first of twenty Royal Air Force Thor squadrons became operational in the UK . The UK deployment carried the codename ' Project Emily ' . One of the advantages of the design was that , unlike the Jupiter IRBM , the Thor could be carried by the USAF ' s cargo aircraft of the time , which made its deployment more rapid , although the launch facilities were not transportable , and had to be built on site . The Thor was a stop - gap measure , however , and once the first generation of ICBM s based in the United States became operational , existing Thor missiles were quickly retired . The last of the missiles was withdrawn from operational alert in 1963 . A small number of Thors , converted to " Thrust Augumented Delta " launchers remained operational in the Anti - Satellite missile role as Program 437 until April 1975 . These missiles were based on Johnston Island in the Pacific and had the ability to destroy satellites in low Earth orbit . With prior warning of an impending launch , they could destroy a Soviet spy satellite soon after orbital insertion . These missiles remain in storage , and could be reactivated , though the W - 49 Mod 6 warheads were all dismantled by June 1976 . Initial development as an IRBM . Development of the Thor was initiated by the US Air Force in 1954 as a Tactical Ballistic Missile . The goal was a missile system that could deliver a nuclear warhead over a distance of with a CEP of . This range would allow Moscow to be hit from a launch site in the UK . The initial design studies were headed by Cmdr . Robert Truax ( US . Navy ) and Dr . Adolph K . Thiel ( Ramo - Wooldridge Corporation , formerly of Redstone Arsenal ) . They refined the specs to an IRBM with : On November 30 , 1955 three companies were given one week to bid on the project : Douglas , Lockheed , and North American Aviation . They were asked to create " a management team that could pull together existing technology , skills , abilities , and techniques in ' an unprecedented time . ' " On December 27 , 1955 Douglas Aircraft Corporation was awarded the prime contract for the airframe and integration . The Rocketdyne division of North American Aviation was awarded the engine contract , AC Spark Plug the primary inertial guidance system , Bell Labs the backup radio guidance system , and General Electric the nose cone / reentry vehicle . Douglas further refined the design by choosing bolted tank bulkheads ( as opposed to the initially suggested welded ones ) and a tapered fuel tank for improved aerodynamics . The engine was developed as a direct descendant of the Atlas MA - 3 booster engine . Changes involved removal of one thrust chamber and a rerouting of the plumbing to allow the engine to fit within the smaller Thor boat - tail . Engine tests were being performed as of March 1956 . The first engineering model engine was available in June , followed by the first flight engine in September . Engine development was complicated by serious turbopump problems . Early Thor engines suffered from what was known as " bearing walking " , whereby the turbopump bearings shift axially within their housing , causing rapid wear and the bearings to seize . First launches . Thor test launches were to be from LC17 at Cape Canaveral . The development schedule was so compressed that plans for the Atlas bunker were used to allow the completion of the facility in time . Nevertheless pad LC17 - B was just ready for the first test flight . The first flight of the Thor IRBM was on 25 January 1957 . The first airframe , number 101 , was delivered in October of the previous year . The vehicle reached an apogee of whereupon contamination destroyed a LOX supply valve causing the engine to lose thrust . The Thor slid backwards through the launch ring and exploded on contact with the thrust deflector . Serious pad damage occurred . The second Thor flight ( 102 ) lasted 35 seconds after an April 1957 launch . It was ended by a range safety officer who destroyed the missile after seeing faulty data on a readout which indicated that the missile was heading inland over Florida . Thor vehicle 103 ( May 1957 ) exploded on the pad during tanking due to a faulty main fuel valve resulting in tank overpressurization leading to tank rupture . Thor vehicle 104 ( August 1957 ) broke up after 92 seconds due to a loss of guidance . Thor vehicle 105 ( 20 September 1957 ) , 21 months after the start of construction , flew downrange . Estimated range without the extra load of the R and D instrumentation was . 1957 saw five more flights , the longest of which covered . Deployment . Thor was deployed to the UK starting in August 1958 , operated by twenty squadrons of RAF Bomber Command . The first active unit was No . 77 Squadron RAF at RAF Feltwell in 1958 , with the remaining units becoming active in 1959 . All were deactivated by September 1963 . All sixty of the Thor missiles deployed in the United Kingdom were based at above - ground launch sites . The missiles were stored horizontally on transporter - erector trailers and covered by a retractable missile shelter . To fire the weapon , the crew used an electric motor to roll back the missile shelter ( essentially a long shed mounted on steel rails ) , then used a powerful hydraulic launcher - erector to lift the missile to an upright position for launch . Once it was standing on the launch mount , the missile was fueled and fired . The entire launch sequence took about 15 minutes . Main engine burn time was almost 2 . 5 minutes , boosting the missile to a speed of . Ten minutes into its flight the missile reached an altitude of , close to the apogee of its elliptical flight path . At that point the reentry vehicle separated from the fuselage and began its descent down toward the target . Total flight time from launch to impact was about 18 minutes . The Thor was initially deployed with a very blunt conical G . E . Mk 2 ' heat sink ' re - entry vehicle . They were later converted to the slender G . E . Mk 3 ablative RV . Both RVs contained a W - 49 thermonuclear warhead with an explosive yield of 1 . 44 megaton s . Thor becomes a launch vehicle . The Thor rocket was also used as a space launch vehicle . It was the first in a large family of space launch vehicles — the Delta rockets . Thor ' s descendants fly to this day as the Delta II and Delta IV . " For RAF Squadrons list : "