Over the Horizon Radar by David Emory, July 2020 & Colin Williams, October 2020
Article six in the RAF Feltwell Loop

One problem which preoccupied America throughout the Cold War was that of providing early warning of any attack from the Soviet Union. One such system involved in attempting to provide this early warning was the 440-L forward-scatter over-the-horizon radar, a component of which was located at RAF Feltwell.

The concept for the system had been developed in the USA, where a research programme was undertaken at Stanford University in 1962-63, and similar work was performed by the Air Force Cambridge Research Laboratories (AFCRL) under project CAME BRIDGE. The early experiments were sufficiently successful that in 1965 a formal programme office was set up by the United States Air Force, with an original target date of August 1968 for a fully operational system. There were a number of delays and changes at the start of the programme, but eventually four transmit sites in the Far East were used, along with five receive sites in Europe. The transmitters sent out a continuous signal in the HF band (5 - 25MHz) which, via ionospheric refraction, would reach the receivers over-the-horizon in Europe. Any perturbation of the signal could be interpreted as a missile launch along the radio propagation path, thus triggering early warning of attack. The transmit sites used were:

    T-1: Wallace Air Station, Philippines

    T-2: Awase, Okinawa

    T-3: Tokorozawa, Japan (HQ in the Far East)

    T-4: Chitose, Japan

The receive sites used were:

    R-1: Cyprus

    R-2: San Vito, Italy

    R-3: Aviano, Italy (data correlation centre)

    R-4: Rothwesten, Germany

    R-5: Feltwell, England

The site at RAF Feltwell formally began operation (with an “Initial Operating Capability”) on 1^st March 1968, being manned by 15 Comm. Sq. OL A1 Unit of the US Aerospace Defence Command. The equipment consisted of highly sensitive receivers (FSQ-76) connected to a large array of tall antennas. Despite official views to the contrary (Historic England state that all that is left of 440-L at Feltwell is a prefabricated hut) it can be seen that there are still some physical remains of an HF antenna array which was probably used in the 440-L system. Just to the north-east of the [PMEL] building, there are eight large square concrete blocks which probably formed the bases for the antennas. They are approximately 11m apart and are aligned such that the main beam would be pointing on a bearing of 42deg, precisely the right direction to receive a signal from the Far East. There are hints of a larger array (with the antenna elements spaced at 30m apart) further to the north-west which may also have been used.

The 440-L system was closed down in 1975, after concerns had been raised about its reliability, and also press reports describing its interfering effect on Japanese television (New Scientist, March 1975). The increasing importance of satellite technology may also have contributed to its closure.

Associated with early warning of attack itself is gaining intelligence on enemy weapon development – such as missile and nuclear testing. Earlier in the 1960s, Feltwell was involved in Project Clear Sky – a joint US/UK programme to monitor the nuclear test ban treaty. As declassified documents now show, a number of techniques were used at RAF Feltwell for this monitoring, including sensors using acoustic, geomagnetic, fluorescence and VLF Phase techniques. Furthermore, a declassified document in the National Archives suggests that RAF Feltwell may also have been involved in a British Over-the-Horizon radar known as Zinnia.

If any readers have additional information about 440-L or any of the other systems mentioned, the author would be most interested to hear from them via the editor. 

I was interested to read the article on OTHR. a story which is long overdue. Mainly truthful it did have inaccuracies.

To set the record I served in the RAF 26 1/2 years. My trade was initially called AIR DEFENCE OPERATOR, later AEROSPACE SYSTEMS OPERATOR basically I was a radar operator. In 1967 I was a Senior Aircraftman (SAC) which is the rank below CORPORAL and basically is the rank that does the work.

I was stationed at RAF Bawdsey when volunteers were sought for 6 weeks at RAF Feltwell 3 or 4 of us arrived here on 7 Sep 1967.

We found that we were working for a civilian organisation with close military ties my service record says the Board of Trade. We working from a Cream "caravan" basically an American articulated trailer. We were operating Project Zinnia. The caravan was situated alongside the present PMEL building. Were paid by postal draft cashed at the P.O. addressed to us at PROJECT 637A.

Whilst in the caravan another RAF team was operating 440L under trial, inside they seemed to be Telecomms tradesmen. 440L had moved from a Southern European country for political reasons. UK was not a good choice because of HF radio reception. Initially operating from Cream caravans, by Sep 67,apart from the caravan we used they had all gone. In the early 90s I noticed the caravans parked up in Derby`s yard down the fen.

Towards the end of 67 new crews were posted in for 440L who were Air Def Ops and I, with my mates were also trained on 440L. Initially there were 4 crews for 24 hr manning comprising a Sgt and 4 SACs. It was later decided that the 4 SACs should be replaced by 4 Cpls.

On the Brit side we started developing a Forward scatter system and with postings I was soon the only SAC qualified on 440L and was sometimes borrowed doing a CPL`s job. It was found that 440l could detect FRACTIONAL ORBITAL BOMBARDMENT SYSTEMS (FOBS) and was rushed into being operational becoming 204 SIGNALS UNIT RAF. We had a Sqn Ldr a Flt Lt and a Flt Sgt with Techies, Stores, Admin and Police all working in PMEL.

The aerial system was FOLDED TRIANGULAR MONOPOLE (FTM) like large inverted spread Vs on each mast. In front buried in the ground were a series of long wires 2ft ish apart. 

Feltwell was an unusual posting as all junior ranks had their own room and all ranks ate in the same mess. We also had a combined Mess for liquid refreshment.

I remember walking passed the Bosses office one day when he came out killing himself laughing, on being asked why he said, "I've just had Strike Command on the phone asking us where we kept our weapons." At which point I laughed as well because we didn't have any.

I will stress that the whole time that I was there 67 - 72 I did not see any USAF personnel working in the (PMEL). There were several US civilians, mostly engineers employed by Raytheon who were developing the system. Late 67 with Zinnia not a success we started to be trained on 440L. Incidentally, I have seen info tying Jodrell Bank with Zinnia.

Zinnia was a backscatter system operating in the HF band (as 440L) with a high powered transmitter based at an old radar station on the Norfolk coast. 

In the late 60s a system called chirp was under development alongside 440L. It was a system to find the best frequency to operate over long distances between 2 points on earth. I believe there was at least one HF transmitter in the far east. It would transmit a signal rapidly changing frequency from 3 to 30 MHZ I don't know the timescale but it could have been over 5 minutes. At our end we had a receiver which changed frequency in unison. It had a speaker and as the scanner swept through we could hear all the other radio transmitters coming through and making a chirping sound. A record was kept of this being printed on facsimile recording paper and looked like red clouds. This was operated by civilian techs. One of these was a US UNI student on his holiday break. He had to come in morning and evening for a half hour or so. However a couple of RAF types were taught what to do and he was able to take whole days off. We loved the jars of coffee he gave us. But what a summer job.

I think this is about as much as I can give you I will try and answer any questions which you may have.

Whilst at Feltwell a local woman got her claws into me and we married in St Mary's March 1972.

Postscript: From an email received shortly after the above was published in the village magazine.

“Had a chat with Mr Stiff who lives by St Nicholas yesterday. He told me that he built the shed which was alongside those Aerials on RAF Feltwell. He didn't know what it was for but was told at the time it was to be used for "Upper Met Research."

From David Emory: “Upper meteorological research” seems to have been a cover name (not entirely inaccurate) used by AWRE and other agencies for radio methods (and perhaps others) to detect nuclear explosions / missile launches. It seems to have been used at Orfordness too, where there was another over the horizon radar (before the more famous COBRA MIST system).

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