Before World War II, Germany had made great advances in the field of radio. By the outbreak of the conflict it had perfected a system of guiding its bombers to their targets at night using narrow beams. Called ‘Knickebein’, it allowed bombers to fly along a precise radio beam pointed at its target. If the aircraft deviated from the prescribed bearing, the signal would change and the pilot was able to correct his direction in order to stay on the beam. Once over the target the bomber intercepted another beam, which became the signal for the warplane to drop its bombs. The system was used operationally against Britain in 1940 and was gradually perfected to become first ‘X-Gerät’, using three intercept beams for more accuracy and then ‘Y-Gerät’, which utilized a single-beam method that triggered a response from the aircraft so the ground controller could determine its position and initiate the point at which bombs should be dropped. All three methods were very accurate navigational tools, far in advance of anything Britain had to offer.
Precise though these systems were – their pinpoint accuracy was amply demonstrated in the destruction of Coventry on the night of 14/15 November 1940 – they were susceptible to jamming by British countermeasures as its scientists gradually discovered more about how they worked. By the end of 1940 most enemy efforts to use the beams had been jammed. Germany was then obliged to turn its ‘blitz’ on Britain against major sites that were easily recognizable from the air, such as London and the large ports of Southampton, Portsmouth, Bristol and Plymouth. It was thus forced to carry out area, rather than precision, bombing.
Leading the task of discovering what Germany was doing in the field of radio was a civilian scientist attached to the Air Ministry’s Scientific Information Branch, Dr Reginald Victor Jones. It was fortunate that the nation had such a man as Jones working in this sphere at that time, for he had a remarkable ability to predict what logical developments could be achieved by the enemy, even before they had become a reality. It was this deductive technical capacity of Dr Jones’s that allowed Britain to keep track of the Germans in the evolution of radar. Germany’s use of narrow radio beams to aid navigation prompted Jones into thinking that they were also using narrow beams for radar, even though many at the top of the scientific world in Britain felt otherwise.
In fact Germany was, as Jones predicted, making startling progress with the idea of using radio beams in the area of radio detection systems. However, unlike the British the scientists and engineers working in this field all belonged to commercial companies and each developed their work more or less in isolation. Systems were built and then demonstrated to the military, rather than progressing in concert with the requirements of the German Kriegsmarine and the Luftwaffe. This tended to slow down advances and lead to inter-service rivalries.
The bespectacled radar transmitter specialist Donald Priest, from the Telecommunications Research Establishment at Swanage, talks to the commander of the Combined Operations support ship Prinz Albert after the raid. Priest went over to Bruneval with Commander Cook’s flotilla as a technical adviser with the understanding that he would go ashore only if the area was totally secure. His knowledge of British radar development made it imperative that he did not fall into enemy hands. (IWM H17356)
By the time war broke out the Kriegsmarine was sponsoring radar work and had on its major warships a serviceable short-wave system (60cm) built and developed by the electronics company GEMA. Known as ‘Seetakt’, it was capable of locating surface ships, in perfect conditions, up to 160km away, but was primarily designed for ranging purposes rather than for detection. Over 200 Seetakt radars were built, a number of which were used for coastal defence. Another system developed by GEMA for the German Navy used long-wave technology and worked in the 2.5-metre waveband at 120MHz. This became known as the ‘Freya’ early warning radar system. It had a range of almost 160km but, unlike the British Chain Home system, could not determine the altitude of any intruding aircraft. The Luftwaffe had little knowledge of these developments until 1938 for the German Navy kept the development work secret. Once Generalfeldmarschall Göring got to hear of Freya’s ability to detect aircraft, the Luftwaffe immediately ordered a number of Freya systems for its own use.
By mid-1940 Britain knew that Germany had some practical radar, but had few details of its size and performance. Intelligence suggested that a system called Freya was employed in France although what it looked like and how it was used was still not known. Dr Jones needed the answers to these questions and knowledge of the actual frequencies Freya operated over, but first a working system had to be located so that it could be carefully studied. There was some suspicion that some kind of radar station on the Cherbourg Peninsula in France had detected the destroyer HMS Delight when it was 30km off Portland Bill and then directed German bombers to intercept and sink the warship. Aerial photo-reconnaissance later indicated that there was an unknown installation close by a compound near to Cherbourg that included known X-Gerät and Y-Gerät transmitters, which might be Freya radar.
Further aerial pictures gave Jones the evidence he was looking for. Careful study of two sequential photographs made on 22 February 1941 showed a rotating antenna around 9m high. In the meantime an assistant of Dr Jones’s, Derrick Garrard, had taken a suitable radio receiver down to the south coast and was listening for enemy radar transmissions. Two days later he succeeded in hearing Freya transmissions around the 120MHz frequency. The two pieces of evidence proved to the Air Ministry that the Germans had radar and were using it.
During the next few months more and more intelligence, supported by technical deductions made by Jones, all indicated that Freya was being used as a long-distance directional radar. It also indicated the existence of another type of radar, called ‘Würzburg’, which was being employed in conjunction with Freya to give short-range information on the height and bearing of intruding aircraft. Intelligence suggested numbers of these two radars working together made up an effective defence line across northern Europe. The Kammhuber Line, as it was called, controlled intercepting German night-fighter groups and directed them on to incoming British bombers. The system was most effective and proving to be costly to RAF Bomber Command.
Jones quickly realized that the technical make-up of Würzburg would need to be analysed so that some sort of jamming arrangements could be employed to counter its effects. It was clear that Würzburg was one of the most important of the enemy’s radars, employing the latest German developments. There was much evidence of its existence, for intelligence sources had claimed to have seen a mysterious parabolic antenna in Germany and listening groups from the TRE had detected pulsed German transmissions opposite Dover in the 50cm waveband at around 570MHz. The information pointed to the possibility that the enemy was employing Würzburg to detect incoming British aircraft as they approached the French coast. Further investigation by scientists from TRE in aircraft fitted with high-powered radio receivers had detected transmissions in the 50cm waveband all along the Channel coast.
Diagram of a German Freya radar of the type based at Bruneval. It was the discovery of this type of installation at Bruneval that helped the British locate the presence of a Würzburg radar on the same site. Experts had reasoned that the inherent efficiency of the Germans would most likely lead them to put the newer radar close by existing Freya equipment. (US War Department)
The picture that initiated the planning of Operation Biting. This photograph, from the archives of Combined Operations, highlights the ‘small black object’ that aroused so much interest in the Photographic Interpretation Section when it was looking for the location of a Würzburg radar installation. It was nothing more than a speck on a photographic plate, but it was the first indication that the radar existed. (Crown Copyright)
Jones now lobbied for aerial reconnaissance photographs to be studied in detail to find one of these elusive and mysterious parabolic antennae. It was accepted that the apparatus worked in the 50cm band and transmitted a pulsed beam with a repetition rate of between 3,600 and 4,000 per second. From this it was relatively straightforward to deduce that the radar had a range of about 40km. Therefore to cover the whole coastline there would have to be one station every 80km along the French coast. The likely sites were narrowed down by employing the theory that the Germans would apply themselves to their normal dictate of convenience and security and locate their Würzburgs in the same compounds as their Freyas.
On 15 November 1941, sortie T/953 by the RAF Photo-Reconnaissance Unit took pictures of the coastline north of Le Havre in France. The Central Interpretation Unit (CIU) staff at Medmenham found Photograph 02Y to be of great interest, for it showed a Freya station located on top of the cliffs along the coast near Cap d’Antifer. Study of the photograph showed a fairly standard layout for the site with the usual large antenna emplacements. Dr Jones’s insistence that these sites should be carefully examined prompted his assistant, Dr F. C. Frank, to scrutinize the photograph in greater detail.
Dr Frank pointed out that a path led along the cliff edge for some distance towards a large villa. It stopped, however, a few metres short of the house in a large loop. At the end of the loop was a small black object, no more that a tiny pinprick on the 12.5cm by 12.5cm contact print that the doctor was studying. Frank suggested that someone had considered it necessary to make a track from the main Freya station to this object. Might it therefore, he reasoned, itself be a radar of some sort?
When the discovery was reported to Jones he used his influence to get the object photographed in more detail. He contacted the CIU and asked for low-level pictures of the installation at Cap d’Antifer, explaining that what he was looking for might resemble a large electric bowl fire. On 4 December 1941 Flight Lieutenant Tony Hill DFC made a photographic reconnaissance sortie over the site and saw the apparatus in question, reporting that it did indeed look like an electric bowl fire. Unfortunately the photographs he took missed the object itself and were inconclusive. Undaunted, he successfully repeated the flight the next day at great personal risk and brought back two incredibly detailed pictures of the installation.
Jones was overjoyed when he received the photographs for they confirmed the existence of Würzburg in the form that he had expected. Its antenna was a parabolic dish with a diameter of around 3m. Its equipment appeared to be housed in a small shed located at the base of the aerial. The whole installation was situated remote from any other building in a low-banked hollow. Close by was a nineteenth-century villa, which no doubt housed the technicians manning the radar installation. The site itself was no more than 100 metres from the cliff edge, with a clear view out to sea.
As Jones and Frank studied the terrain surrounding the radars, they were struck by the openness of the compound. It was perched close to the cliff’s edge with a path running down to a small beach. To its rear was wide-open countryside with no town of any significant size nearby. Its vulnerability to attack was plain to see. The idea began to form in their minds of a raid being mounted to steal the radar. The component parts of the Würzburg if studied at first hand would yield any number of enemy secrets. Jones was at first loath to suggest anything that might cause any loss of life, but possession of the radar could help stifle the enemy’s advances in the use of radar and might help shorten the war. It was a risk that, on balance, was worth taking.
