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The GCHQ Years - 1963 - 1993

"Spooks and Experiments"





Article by Chris Morshead

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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 German systems such as “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” (CG&CS) in 1919, became an indispensable organisation which played a key role in the defeat of the Nazis and the Axis powers.


After WWII, in 1946, CG&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 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, 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 Middle and Far East.


In October 1948, over a weekend known as “Black Friday”, the Soviet Union changed it’s crypto systems - the West lost its ability overnight to “read” Soviet coded messages. 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”.


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.  Some of the surviving RAF WW2 buildings may have been used to house experiments, as well as the Purley Farm House, once home to farmer Bert Clifford and later commandeered as engineers quarters next to the airfield technical site.

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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 to study a wide range of phenomena, not just Military. This included such things as Oceanic Research, using this OTHR to study sea conditions (wave heights, direction of movement, speed of movement etc) out in the Atlantic Ocean beyond Ireland. The organisations included various Universities, the Institute of Oceanographic Sciences, the Meteorological Office, the Royal Signals and Radar Establishment (RSRE) based at Malvern and even the National Air Traffic Services (NATS). This work partnered, in many cases, with countries across the world – including, in some cases, the Soviet Union – and ran for many years, we think over 30 years. Clearly, partners were carefully chosen depending on the topic being studied at the time and not all “partners” would have access to the site!

A green research lab

Copies of overhead projector slides showing (ABOVE) the proposed NATS (National Air Traffic Services) trial to provide radar cover over the Atlantic and (RIGHT) the Radar cover for JASIN 1978 (Joint Air Sea Interaction Project) The order OTHR radars used were both located at Blakehill Farm (source from the Pof Ramsay Shearman Collection via the Malven Radar and Technology History Society)

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The organisations using Blakehill included various Universities, the Institute of Oceanographic Sciences and the Meteorological Office. Even the National Air Traffic Services (NATS) conducted assessments into the provision of ATC Radar cover into the North Atlantic – interestingly, there is still no Radar cover over the Atlantic though Ireland are now looking at providing some – in 2020!

Evidence for 3 Over The Horizon Radar Sites

So far, we have found evidence of 3 possible OTHRs here at Blakehill Farm which, based on their locations and orientation on the Airfield, we believe were used as follows:-

PDash Extreme Northern point - post rema

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


Below - OTHR #2 - JASIN (possible) was approx 425m long and looked North into the area between Scotland and Iceland and as used for Oceanic Research and, possibly, Military Research. The “scar” for OTHR #2 is formed by a 1.5m wide concrete base stretching the entire length PRIVATE LAND NO ACCESS

Below - OTHR #3 - TEST AN/TPS71 POTEEN (possible) was approx 300m long and looked North into the area North of Scotland and may have been a Test Array for a proposed Military OTHR, an AN/TPS71 which, due to the Cold War ending in 1991, was never installed –  Interestingly, it would have dwarfed the Test Array as the AN/TPS-71 array would have been 2600m long – wider than the Airfield!


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. However, 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 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 system similar to the 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 know of at least five extremely large arrays constructed at Blakehill used for Direction Finding, Over the Horizon Radar and Target Location as well as Wavefront Analysis. We also know of many other temporary arrays located at Blakehill. As well as looking at long-range HF work, it would not be surprising if shorter range communications were not tested as VHF and UHF communications 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 – maybe one day GCHQ will reveal some of what was studied here

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 Blakehill Farm was quite possibly involved in developing 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 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”. Other studies in the 1980’s looked at the effects of a Nuclear blast on HF Radio Communications.

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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.

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 carried out here on site.    That such work was taking place is very clearly highlighted by the Flixborough Chemical Plant explosion in 1974. It was a system, probably quite similar to the ones used for Operation IVY Ionospheric research which, inadvertently, proved its effectiveness in 1974 when a huge chemical explosion at Flixborough, North Lincolnshire was detected at Blakehill Farm while conducting some research work using Radio Waves bounced off the Ionosphere. During an unknown trial, Blakehill happened to be monitoring 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. 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 highly unlikely that GCHQ would not have been doing their own research using this 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 GCHQ moved its 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. 

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