GCHQ & Radar Experiments | rafstationblakehill

The GCHQ Years - 1963 - 1993

"Spooks and Experiments"

Article by Chris Morshead - updated June 2024

Few people will not have heard of Bletchley Park, famed for the WWII production of “Ultra” intelligence material, some of which came from decoding messages from the infamous German “Enigma” cypher machines, a task greatly assisted by Polish cryptanalysts who led the way in breaking “Enigma” in the run up to the War.

Subsequent coding devices such as the German “Lorenz” and the Japanese “Purple” cypher machine all contributed to the gathering of SIGINT – Signals Intelligence - by the UK and the USA. Britain’s Intelligence Agency, originally formed as the “Government Code and Cypher School” (GC&CS) in 1919, became an indispensable organisation which played a key role in the defeat of the Nazis and the Axis powers through WWII.

After War, in 1946, GC&CS relocated to Uxbridge on the outskirts of London and a new title appeared for it; GCHQ (Government Communication Headquarters). However, it was soon clear that new threats were rapidly emerging out of the ashes of WWII, the principle one being that of the Soviet Union and the Warsaw Pact. It was realised that GCHQ would need to expand to meet this new threat and to monitor the Soviet crypto machines such as “Crystal” and “Albatross”. In 1948, a new home for GCHQ was found – in Cheltenham - where it still operates from to this day.

As the Cold War intensified and with development of larger atomic bombs, long-range strategic bombers, nuclear-armed ballistic missiles which could be launched from land – or from submarines – and the growing conventional Armed Forces of the Warsaw Pact, it became the role of GCHQ, in conjunction with their US partner, the NSA (National Security Agency), to harvest “INTEL” (Intelligence) on all these threats, providing reliable, timely and accurate information to both the Government and the Armed Services. In short, GCHQ were our eyes and ears and noses, located around the world, searching out the smallest bit of information which could be key to our National Defence from SIGINT bases in the UK, the Mediterranean and the Middle and Far East.

Then, in October 1948, over a weekend known as “Black Friday”, the Soviet Union changed its crypto systems – and the West lost its ability overnight to “read” Soviet coded messages. From that point on, techniques such as T/A (Traffic Analysis), where coded signals are traced even if they are impossible to read, became the mainstay of SIGINT. In 1963, to enable GCHQ to continue to develop and maintain its technological edge in the field of T/A and other SIGINT techniques using things such as HF/DF (High Frequency {Radio} Direction Finding), RAF Blakehill Farm was handed over to GCHQ as a Communications “Research Site” where such techniques were tested and refined and new ideas trialled.

For the next 30 years, Blakehill Farm was “home” to a huge number of trials based on cutting-edge research, both in Communications and other applications of radio as detection or monitoring systems including various long-range HF Over The Horizon Radars (OTHRs) capable of detecting targets several 1000 miles away. Some of the surviving RAF WW2 buildings may have been used to house experiments, as well as buildings such as the Purley Farm House, once home to farmer Bert Clifford and later commandeered as engineers quarters next to the airfield technical site.

The rather “low key” GCHQ Experimental Radio Station sign which used to be at the entrance to RAF Blakehill Farm. The half piece of paper (bottom left of sign and enlarged image) would have informed the reader that the site came under the “Official Secrets Act”.

It is clear that the facilities were used by a huge number of Research Organisations, both Military and Civilian, to study a wide range of phenomena, not just Military. This included such things as Oceanic Research, using various OTHRs to study sea conditions (wave heights, direction of movement, speed of movement etc) out in the Atlantic Ocean beyond Ireland out towards Iceland. The organisations involved in this and other work included various Universities, the Institute of Oceanographic Sciences, the Meteorological Office, the Royal Signals and Radar Establishment (RSRE) based at Malvern and even the civilian air traffic service providers, now known as National Air Traffic Services (NATS). This work partnered, in many cases, with countries across the world – including, in some cases, the Soviet Union. Clearly, partners were carefully chosen depending on the topic being studied at the time and not all “partners” would have access to the site given some of the highly sensitive work being carried out at Blakehill Farm!

A green research lab

Copies of overhead projector slides showing (above) the proposed NATS (National Air Traffic Services) trial to provide Air Traffic radar cover over the Atlantic and (right) the Radar cover for JASIN 1978 (Joint Air Sea Interaction Project – read on for further information). The order OTHR radars used were both located at Blakehill Farm

From the Pof Ramsay Shearman Collection via the Malven Radar and Technology History Society via Hugh

Evidence for 5 Over The Horizon Radar Sites

So far, we have found evidence of 5 possible OTHRs here at Blakehill Farm which, based on copies of reports and/or their locations and orientation on the Airfield, we believe were used as follows:-

Below OTHR #1 - SKYWAVE (confirmed) was approx 300m long and looked West over Ireland and was used for Oceanic Research as well as ATC Radar Research and, possibly, Military Research. MOSTLY PRIVATE LAND LIMITED ACCESS

The “Skywave” Array when in use. The signals to and from the array were collected in the white cabinets which were then connected back to the “Whitworth Building”, out of sight but a short distance to the right of this picture. The “Whitworth Building” is still in use today – by the Wiltshire Wildlife Trust for rather different purposes!Photo - Prof Ramsay Shearman collection via the Malvern Radar & Technology History Society via Hugh Williams

PDash Extreme Northern point - post rema

All that is left of the “Skywave” Array today looking along where the row of central masts ran. The first post hole from the nearest central mast can be clearly seen in the foreground. As can be seen, a fence and metal gate have now been installed between where the 1st and 2nd central masts were installed

Below - OTHR #2 - Unknown (possible) was approx 425m long and looked North into the area between Scotland and Iceland. It may have been used for Oceanic Research and, possibly, Military Research but it’s role is effectively “unknown” at this time and there is no photographic evidence of an actual array. The “scar” for OTHR #2 is formed by a 1.5m wide long, narrow, concrete base. stretching the entire length PRIVATE LAND NO ACCESS

The view looking East along a clear scar which crosses the main Runway.

Below - OTHR #3 - The Low Power Sounder Experiment (LPSE) OTHR was set up in the late 1980’s. The array was approx 300m long and looked North into the area North of Scotland between Iceland and Norway and up into the Norwegian Sea. This was a receiver Test Array. The associated transmitter arrays were based, initially, at Cobbett Hill near Guildford in Surrey and then, later, using a specially constructed Transmitter Array at RAF Greatworth near Banbury in Oxfordshire. LPSE was used to study reception conditions for a proposed new Military OTHR to be installed at Blakehill Farm under Project Poteen in the early 1990’s to cover the area between Iceland and Norway to provide early warning of the movement of Soviet ships and aircraft from the Soviet military bases in the North-Western USSR into the Atlantic. Following early success with LPSE, the array was slightly enlarged to give the Low Power Sounder Extended Experiment (LPSEE) in support of additional research work ahead of Poteen.

View along the area where the LPSE/LPSEE array was located. It is not known what caused the scar itself but it could be where the fence once stood (see photo below). Given the light-weight nature of the array itself, there are no physical indications of the antenna masts or the associated cabling which seems to simply have been laid on the surface. Photo Vince Povey

View from one end of the LPSEE array. In the middle distance, a small hut can be seen which provided the terminal for the associated cables running from the antennas. The central SN/FLR-9 type array (it is quite hard to make out the outer circle in this photo) can be seen behind in the middle of the airfield but it was not involved in the LPSE/LPSEE trials. Photo circa 1987/1988 via Colin Clutterbuck.

Location of LPSE/LPSEE transmitter sites (initially at Cobbett Hill then at RAF Greatworth) with the Receiver arrays located at RAF Blakehill Farm.Map by Chris Morshead based on Google Maps

A general view of the busy “aerial farm” at RAF Greatworth. Inset is the Transmitter Array set up specifically to support the LPSEE trials at Blakehill Farm. While Greatworth is only about 40 miles from Blakehill Farm, the route taken by the signals to Blakehill would have been via the area somewhere NE of Iceland in the Norwegian Sea – a total round-trip distance of some 2500 – 3000 miles! Main Photo:- Anonymous donor to the RAF Greatworth Website at www.raf-greatworth.com via IanInset Photo:- Prof Ramsay Shearman collection via the Malvern Radar & Technology History Society & Hugh Williams

The final Production Radar which was to have been installed at Blakehill Farm under Project POTEEN was an AN/TPS71 Relocatable Over-the-Horizon Radar (ROTHR) which, due to the Cold War ending in 1991, was never actually installed (see https://www.rafblakehillfarm.co.uk/poteen-an-tp-s71-blakehill for more details). Interestingly, the Radar itself would have dwarfed this Test Array as the AN/TPS-71 array would have been 2600m long – wider than the Airfield itself so additional land would have been purchased for it fit on!

OTHR #4 – Rhombic and Delta Arrays – Over time, various temporary Rhombic and Delta Transmitter arrays were located close to the Whitworth building to undertake OTHR research including the Joint Air-Sea Interaction (JASIN) Experiments in the late 1970’s off Rockall to the North-West of Scotland. This research work included up to 14 ships and numerous buoys which were used to measure the sea state in an area of the Atlantic near the Rockall Bank. At the same time, transmitters in the Whitworth Building fed whichever array was to be used to monitor the area by Radar. These transmitter arrays were located in the field across the perimeter track from the building. The returning signals from the Atlantic were received using the circular AN-FLR-9 type array (https://www.rafblakehillfarm.co.uk/blakehill-anflr9-cold-war) located in the middle of the airfield. The GCHQ staff operating this circular array were not part of the JASIN team but kindly passed the received data back to the researchers in the Whitworth Building for further analysis. The circular array was affectionately known as “Belle Anna” or the “Beautiful Ring” as recalled by one of the researchers who worked in the Whitworth Building on the JASIN programme.

An artist’s scaled impression of a 30m vertical Delta Antenna Array. The Array was 30m tall with a base width of 60m with the base arms 3m off the ground. A smaller 20m Delta array was also used, and possibly to simplify construction, used the same upright pole but with the black antenna wires attached lower down but with the same base span of 60m. Rhombic antenna are constructed in a similar manner, the largest being of similar dimensions (30m tall x 60m wide). The black dotted line shows the transmitter feed line running from where it crossed underneath the perimeter track on its way from the Whitworth building. The location of the FNP-9 type “Belle Anna” array used to receive the returning signals is indicated by the red ellipse. Finally, for information, the location of other known/suspected OTHRs are indicated.Source – Vince Povey annotated by Chris Morshead

The “boffins” from Birmingham University and the Appleton Labs then compared the received radar signals with the actual data collected by the ships and buoys, the aim being to perfect the ability to remotely read the sea-state using OTHR. These arrays were changed depending on exactly what experiments were being carried out at the time. Sadly, given the nature of their construction, there are no traces of these Transmitter arrays on site though the original cable-run can be made out running across the perimeter track near the Whitworth Building.

OTHR #5 – UnknownA further possible OTHR array, similar in construction to the LPSE/LPSEE linear array, appears in a photograph of Blakehill Farm running from middle-bottom diagonally right (3 antenna masts shown in total – we don’t know how many there were in total). There is no information available on the use of this array.

Three elements of a potential linear antenna array in the foreground near the old Tech Site viewed from the AN-FLR-9 type antenna. It is not known what this array was used for.Image via the Malvern Radar & Technology History Society via Hugh Williams

Other military work was conducted by organisations such as the Royal Signals and Radar Establishment (RSRE) based at Malvern but no details have been released by GCHQ of their own work here at Blakehill Farm to date though odd reports jointly written by GCHQ staff have been seem. Based on what we know of the many aerials which were located here in addition to the OTHRs, much of the work will have involved developing and perfecting key SIGINT (Signals Intelligence) and COMINT (Communications Intelligence) techniques in use at the time based on the monitoring of long-range High Frequency (HF) radio communications.

This involved work on HF Direction Finding (HF DF) using the large circular central array similar to a SN/FLR-9 array, as well as to work out how we could use HF signals for both communication and the detection of other peoples HF Radio traffic and even using the Ionosphere in other ways.

We also know of many other temporary arrays located at Blakehill but have no evidence apart from the now distant memories of people who have lived near Blakehill Farm and we don’t know what these arrays were used for. As well as looking at long-range HF work, it would not be surprising if shorter range communications were not tested here as well.

However, as VHF and UHF communications operate at much higher frequencies, they require very much smaller aerials; there will be no traces of those left on the site. It is unlikely that trials with satellites took place here unless mobile dish aerials were used.

RAF Blakehill Farm and the Atomic Bomb Link

We do know that monitoring the development of Soviet Nuclear weapons was a key task for GCHQ and their counterparts in the USA, the NSA, work which was formalised under Project Blue Sky in 1964. While Blakehill Farm was not formally allocated as part of Blue Sky, the GCHQ Research Station at Blakehill Farm was quite possibly involved in developing and improving equipment and techniques for such work.

For example, it was soon realised that the Ionosphere would “bend” due to the huge blasts from the Soviet nuclear tests so much work was done in the USA and the UK to see how this “bending” could be detected and used in this way. Many, once Secret, US reports dating between the 1950’s and 1980’s, tell us, for example, where, for Operation IVY, Ionospheric measurements were taken during the US Nuclear Test programme and where it was noted in the report that it was a useful technique as a means of long-range detection of large nuclear explosions, “possibly as far away as 4500km” [2800 miles]. Other studies in the 1980’s looked at the effects of a Nuclear blast on HF Radio Communications.

Above - Copies of some of the once Secret reports released by the United States covering research into the detection, measurement and effects of Nuclear explosions on the Ionosphere and HF. The Americans made use of the US Nuclear Test Sites, both in the Pacific and also mainland USA to carry out such trials during Test detonations of Nuclear and Thermonuclear Weapons. Similar work in the UK took place at Orford Ness, Suffolk.

While there are certainly no known reports of Nuclear detonations going on here at Blakehill Farm, the same detection and measurement techniques could easily have been developed and carried out here on site – even if somewhat by accident at times!

This was very clearly highlighted by the Flixborough Chemical Plant explosion in 1974. The University of Leicester were conducting research into the propagation of VLF Radio signals as part of the NATO Advanced Study Institute programme when, on 1st June 1974, a huge chemical explosion occurred at Flixborough, North Lincolnshire. The blast was detected in the 4.78MHz HF radio test signals being received at Blakehill Farm which was being used as a Receiver Site as part of this research project along with one at Leicester itself. At the time of the explosion, Blakehill happened to be monitoring the test signals being transmitted from Stafford, Upwood (Cambridgeshire) and Gainsborough (not far from Flixborough) when, all of a sudden, a major “flexing” of the Ionosphere was observed causing a disturbance in the received signals. Work was done to try and estimate the size of the blast as well confirm its location. Interestingly, that information from 1974 was still being analysed in 2003 by different Research Scientists around the world.

An extract from a 2003 report in the “Journal of Atmospheric and SolarTerrestrial Physics” showing the effects of the Flixborough explosion on the three signals from Stafford, Gainsborough and Upwood. Identical techniques could be used to detect and measure any explosion, including Nuclear Weapon explosions, using mysterious-sounding techniques such as “Wavefront Analysis”.

While the known studies we have found just looked at size of the chemical explosion at Flixborough, it is quite possible that GCHQ and other military organisations at Blakehill Farm could have been doing their own research using these sort of technique - and others - for detecting and measuring Nuclear blasts – indeed, one would really hope Britain was “keeping pace” in such vital “Cold War” research so the Government and Military planners could be kept abreast of the latest developments in the Nuclear arsenal of the Soviet Union. One day, it is hoped that such stories may be told when the Archives at GCHQ are opened up.

The end of testing - 1997 - 2000

In 1991, the Cold War ended and the Warsaw Pact broke up releasing the “Peace Dividend”. For GCHQ in particular, the emphasis shifted away from Nuclear confrontation and, particularly with the advent of the Internet, Fibre-optics and Satellite communications, the way information was passed around the world changed rapidly.

Blakehill Farm simply did not have the infrastructure to support such research work and so the site was eventually handed back to the MoD in 1997 and organisations such as GCHQ moved their research work elsewhere.

The site was finally cleared of all remaining aerials, cables and other remaining equipment by 2000 when 240 hectares were sold to the Wiltshire Wildlife Trust as a nature reserve, some of the remaining land being returned to the local farms.