Bloodhound was the RAF's only long range / heavy SAM and was in service until 1989. The ramjet powered semi-active guided missile can trace its history back to 1949 when Bristol Aircraft Company set up Project 1220 to develop a surface to air guided weapon (SAGW) to protect the v-bomber airfields from Soviet air attacks. This project was to fulfil what was called "Stage 1 Air Defence" and while providing a air defence role, was really only useful to provide the RAF with experience of deploying guided weapons until the more advanced "Stage 2" was developed and in service in the early 1960s

Project 1220 was assigned the Ministry of Supply codename "RED DUSTER". Bristol's believed that to get a decent performance, particularly range, for a SAGW, a ramjet would provide superior performance to that of a rocket powered weapon. Bristol's engine department commenced work on development of a ramjet for Red Duster and worked closely with Boeing Aircraft and the Royal Aircraft Establishment. The guidance system for this missile was to be developed by Ferranti.

A series of test vehicles were developed and flown, called eXperimental Test Vehicles or XTV, with XTV.1 to XTV.5 being used to develop the aerodynamics, propulsion system and Ferranti guidance system. The final test vehicle was called XRD, eXperimental Red Duster and was more or less the definitive Bloodhound I.

The next stage in development were the Service Acceptance Trials (SAT) with the test missiles, the Service Acceptance Vehicles (SAV) being fired at the Woomera range. Initial XRD.1 performance was very disappointing, mainly due to the ramjets, which used a flare to maintain combustion. This meant that the missile range was restricted to the flare's burning time. In the initial trials of XRD.1 the RAF were so disappointed that they cancelled an order for Red Duster and ordered the rocket powered English Electric Red Shoes, later called Thunderbird I.

Since Bristols had already been contracted to supply Australia and Sweden with Red Duster, Bristols had to sort out the problem. Quickly. This was fixed by changing the ramjet combustor to a design used by the National Gas Turbine Establishment (NGTE) for its ramjet test vehicle. The difference was that the NGTE combustor used a separate pilot combustor, rather than a flare, to keep the main combustor lit. Thus was born XRD.2, which entered RAF service as the Bloodhound I in 1958.

Early SAGWs used a beam-riding guidance system, but this was somewhat primitive, so a semi-active guidance system using pulsed radar was selected for Red Duster. As development progressed, it was becoming clear that pulsed radar was susceptible to jamming and had a poor low-altitude performance. As better radars were developed, Continuous Wave radar became the preferred choice. It also became clear that the Soviets would soon have supersonic bombers carrying stand-off missiles in service by the end of the 1950s. So, a faster longer ranged missile was required.

By 1955 it was thought that a missile to meet the Stage 2 air defence requirements was beyond the state of the art, so a pair of intermediate stages were added. As mentioned above, English Electric had developed a SAGW called Red Shoes for the Army. Since the army mainly dealt with low-level threats, continuous wave radar should be applied to Red Shoes, producing Yellow Temple, later called Thunderbird II. Modifying the Thunderbird to use CW radar produced what was called Stage 1 1/2. Bristol's pondered fitting Bloodhound I with CW guidance, producing "Super Bloodhound" but were putting their money on another missile project.

To meet a long range high-speed threat required a faster longer ranged missile, with mid course update and semi-active terminal homing using CW radar. The missile, called Blue Envoy, was to be Stage 1 3/4. Blue envoy used CW radar and improved ramjets that were designed around the NGTE combustor system. By using the NGTE combustor Blue Envoy could accelerate and climb using pilot and main combustor, but once in a cruise, could shut down the main combustor and cruise on the pilot combustor alone.

 Blue Envoy (Stage 1 3/4) was cancelled in 1957, as was Stage 2, leaving Bristol with no SAM work to follow Bloodhound I. After being told of the cancellation, some engineers from Bristol were sharing a taxi with a engineer from Ferranti. The Ferranti engineer suggested doing what the aircraft people had been doing for years, i.e. modifying the engine and systems to produce a new model.

This was done, by way of adding CW guidance and the ramjet improvements from Blue Envoy, to produce QF.169, Bloodhound II. This entered service with the RAF, RAAF, Swedish and Swiss Air Forces, remaining in service until the 1990s. Development of the BS.1009 Thor engines for Bloodhound III required further XTVs, 11 to 17.

Various proposals for Bloodhound variants included RO.166, the Mk III with command guidance and a nuclear warhead and the Mk IV, which was a mobile version, proposed for the Army based on the experience of the Swedish Air Force. A further variant was Naval Bloodhound, which used the Bloodhound systems in a new airframe. Bloodhound 21 was a mobile export version with reduced ECCM capability.

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