Night Raid

by Taylor Downing

  Using this information, by the autumn of 1941 Jones was able to report to the Air Ministry chiefs in great detail about the Freya system. Each station, he said, consisted of two sets of antennae, one acting as standby or reserve for the other. A rotating aerial was mounted on a turntable, as was the operator’s cabin, complete with transmitting and receiving equipment. The aerial antenna was both transmitter and receiver and operated, Jones calculated, on a waveband of 2.3–2.5 m. Freya could operate at various ranges, from a distance of about ninety miles to as close as about a mile and a half. The reports picked up from the stations suggested an accuracy of about half a mile. The equipment was capable of 360-degree rotation, but once an enemy aircraft was sighted the Freya usually only rotated within the few degrees needed to keep it in sight. Jones was even able to report that the equipment was made by AEG in Berlin and the operators probably used cathode ray tubes on which to base their plots.

  From aerial photographs it was possible to calculate that each station was manned by an officer and about thirty men, usually from the Luftwaffe but sometimes with Wehrmacht and Kriegsmarine personnel present. In 1941, the organisation of the system came under control of a new Luftwaffe unit called Luftgau Nachrichten-Regiment 12 (the 12th Signals Regiment of Luftwaffe Regional Administration). Jones estimated that there were as many as 150 Freya stations in operation.9

  Jones also realised that the Germans used a grid system made up of rectangles measuring about 1 km east–west and 0.75 km north–south in which to plot the approach and passing of Allied aircraft. This approximately matched the accuracy of the Freya network. However, in late 1941 bomber crews began sending back reports of a significant increase in interception by enemy fighters at night. The Germans seemed to be using something far more accurate than could be expected from the Freya network. In addition, the enemy fighters always seemed to be at exactly the right height to intercept the Allied bombers – and Freya was not good at detecting height. For some time the boffins at TRE had been picking up signals which appeared to come from a completely different German radar system, operating on a much shorter wavelength of 53 cm.

  Jones realised that, once again, this had been predicted in the Oslo Report. According to the report’s author this system used paraboloid or bowl-like reflectors. Jones calculated that they would probably have to be about ten feet in diameter. This would mean that the whole installation was probably half the size of a Freya antenna.

  The word that came up a few times in intercepted messages was of another system called ‘Würzburg’. But what did this mean? How did the so-called Würzburg link into the Freya radar chain? Was it some newer and far more accurate radar system? If so, would this disrupt and potentially lead to the cancellation of the bombing offensive against Germany? Moreover, would it ever be possible to find anything as small as one of these new radar installations along the coast of occupied Europe? This was the next challenge the British scientists faced.

  8

  Photo Intelligence

  R.V. Jones had built up a strong working relationship with some of the interpreters whose job was to analyse aerial photographs. In April 1941, the entire photo intelligence community had finally moved from the primitive conditions of their first headquarters in Wembley, where the roof of the building leaked and many of them had to work beneath umbrellas to keep dry when it rained. A new organisation called the Central Interpretation Unit was opened in a grand country house that had been requisitioned on the banks of the Thames between Marlow and Henley. A splendid mock-Tudor building with tall chimneys and magnificent gardens with views along the Thames valley, its name was Danesfield House.

  The photo interpreters could barely believe their luck. From the trials and tribulations of trying to work in a busy suburb of London during the Blitz, they now found themselves laying out their photos and equipment in the grand wood-panelled halls of a turn-of-the-century mansion. The exterior of the house was swathed in wisteria, whose delicate scent drifted inside during the summer months. Danesfield even had central heating, which was extremely rare at the time. And instead of commuting through the bombed streets of London, the photo interpreters were now billeted in luxurious houses in the countryside of the Chilterns. One photo interpreter stayed in the lodgings of a wealthy businessman where a butler who had formerly worked for a duke woke him every morning with a cup of tea. The new establishment, called by the RAF, like all air force stations, after the local village, was named RAF Medmenham.1

  The RAF was in the process of inventing nothing less than an entirely new science: that of photo interpretation. The analysis of aerial photographs was broken down into a number of stages. First Phase was carried out at the airfield. As soon as the reconnaissance aircraft landed, ground crew collected the film from the aircraft’s cameras and rushed it to be processed and printed. A photo interpreter was on hand to examine the photos and to provide an immediate analysis of urgent tactical questions. Was that ship still in the harbour? Had that squadron of German fighters deployed at the airfield? Were those Panzer tanks still sheltering in the same place? Had a bombing raid succeeded in hitting the target? This intelligence was passed on within three hours of the aircraft touching down.

  Then the aerial photos were taken to Medmenham, where Second Phase photo interpreters put together a more considered daily intelligence briefing. Interpreters worked in shifts around the clock to produce this report. Second Phase usually involved some form of numbering or measuring of the details on the photos. By counting the aircraft lined up on an airfield the interpreters could see if a new squadron had deployed to that particular base. By measuring the dimensions of a group of buildings they could calculate the storage capacity for coal, fuel or munitions. By measuring the width of a bridge in front of an intended advance they could predict whether it was strong enough to support Allied tanks.

  Finally, the photos were passed on to Third Phase, in which a range of experts divided into sections would examine the photos in yet more detail. The aircraft specialists could spot not only if the numbers of aircraft on an airfield had changed but if a new mark or design of German aircraft had been photographed. The shipping experts could see if a new keel had been laid in a shipyard, and if so could predict what vessel was under construction and when it would be completed. The industrial experts could examine a factory and calculate exactly what it produced and what its annual output would be. In their damage assessment reports after a bombing raid the photo interpreters could calculate precisely how much damage had been done and how long it would take for the factory to be back in production. They could even recommend, if necessary, the optimum time to bomb the factory again, when maximum effort had been put in to rebuilding it but before it was back at full production.

  The RAF recruited an extraordinary mix of academics, boffins and mavericks to work at Medmenham. Not only did they need individuals with particular expertise, they also needed problem solvers who could deduce what the enemy were up to simply by looking at a set of photos. Archaeologists were especially good at this as they were used to making deductions from fragmentary evidence. So the entire Archaeology Department at Cambridge University was recruited, from the senior professor to the most junior research fellow. Geologists, physicists, mathematicians and other scholars joined them and Medmenham soon acquired an intensely academic atmosphere. One young graduate nervously arriving for his first day was astonished to find that the first person he met on arrival was his old college botany tutor. But musicians, artists, cartoonists and showbusiness people also found their way to Medmenham. An Oxford professor would give a talk one evening, while the next night West End entertainers would lay on a show or a musical concert. The photo interpreters formed a sort of elite within the RAF.

  Women were found to be particularly good at the detailed, painstaking work of photo interpretation and were recruited as WAAF officers to do exactly the same job as the men. The RAF even put women in charge of some of the teams. The formidable Constance Babington Smith, known as
‘Babs’, had been a journalist on The Aeroplane magazine before the war and at Medmenham led the Aircraft Section. Later in the war she was to discover the first V-bombs at their research establishment at Peenemünde and the first Messerschmitt jets before they were rolled out for combat. Uniquely in the British war effort, female officers doing equal work with men were in command of male officers.2

  And the only weapons the photo interpreters used were slide rules, magnifying glasses and pairs of optical glasses that enabled them to work in 3D – or, as they called it at the time, Stereo. By this means they could measure objects like small radio transmitting aerials or radar towers with remarkable accuracy.

  As the war progressed the RAF photo interpreters were able to extract ever more accurate tactical and strategic intelligence from aerial photos. While the codebreakers at Bletchley Park produced startling revelations by cracking the German Enigma communications, an immense amount of day-to-day information about enemy activities came out of the work of the photo interpreters at Medmenham. An American general, Lee Chennault, later claimed that 80 per cent of all intelligence in the war had come from photo intelligence.3

  Claude Wavell was a brilliant mathematician who before the war had been working on a commercial project using aerial photographs to map Rio de Janeiro and other parts of South America. At the outbreak of war, one of the leading figures in photo interpretation got in touch and asked him to come back to Britain to join the RAF team. He hesitated at first, but after hearing of the evacuation at Dunkirk his patriotic spirit got the better of him and he cabled his friend saying ‘If you still want me, I’ll come.’ He received a telegram back almost immediately that read ‘Come at once.’

  So Wavell joined the small group learning photo interpretation for the purposes of military intelligence. He soon began to specialise in the identification of aerials, towers and transmitters, and was put in charge of the team known as G Section. It was on this work that he first met and got to know R.V. Jones. It was Wavell who spotted the first Knickebein transmitters at Cleves that helped to guide the German bombers in the summer of 1940. And, a few months later, it was Wavell who first drew Jones’s attention to the tiny circular installations with what appeared to be rotating antennae near Auderville.

  By the end of 1941, Wavell and his team had found a total of fifty Freya sites along the enemy-occupied coast from western France to northern Norway. However, the task of studying thousands of square miles of occupied Europe to find the smaller Würzburg German radar stations, probably only ten feet in diameter, was going to be like looking for a needle in a haystack. However, Jones guessed that the Germans might well site the Würzburgs near to the Freyas so as not to have to build and defend additional radar sites. So he and his assistant Charles Frank asked Wavell to send them the aerial photos of all existing Freya installations. They started searching these one by one. It was Frank who made the first dramatic sighting.

  On top of the cliffs not far from Cap d’Antifer, about twelve miles north-east of the French port of Le Havre, was a radar encampment with two Freyas. Frank noticed that a track appeared to run for a few hundred yards from them to a large and rather flamboyantly designed villa further along the cliff top that was presumably the headquarters for the radar station. However, he spotted that the track did not run right up to the villa but seemed to end in a loop a short distance from the house. Why would the track stop short of the villa? Near the loop there was a tiny blurred speck, so indistinct that Frank asked for repeated photographic cover of the site to check that it was not just a speck of dust on the photographic negative. But there definitely appeared to be something there. On a hunch that this just might be what they were looking for, Jones put in a request for a low-level sortie to take a closer look and photograph the site. Mindful of the fuss he had caused the last time he had requested such a ‘dicing mission’, Jones made it clear that this was only to be done when conditions were entirely favourable. Then he telephoned Wavell at Medmenham to tell him of his suspicions.

  Most reconnaissance sorties were flown out of RAF Benson, a station centrally located in Berkshire and only a few miles from the Central Interpretation Unit at Medmenham. The pilots used occasionally to pop over to Medmenham to chat with the interpreters in order to get a sense of how their photographs were being used. It so happened that a couple of days after Jones had put in his request, two Spitfire recon pilots were at Medmenham chatting with Claude Wavell before going out for a few beers. One of these pilots, Flight Lieutenant Tony Hill, was every schoolboy’s idea of a hero. With his combed-back hair and a silk scarf under his flying suit, he presented a glamorous figure. He had a laid-back, devil-may-care attitude but was utterly determined to persevere with a task until it was complete. And he never ducked tough assignments. It was as though he thrived on the risk.

  Wavell showed Hill the photograph that Jones and Frank suspected might include the new type of German radar and explained how important it was to find this final piece of the jigsaw. Jokingly, he said to Hill and his friend, ‘You pilots annoy me! You go over this place time and time again but you never turn on your cameras.’ Hill stared hard at the photograph. He asked if the tiny speck really could be the device that completed the story of German radar and Wavell assured him that this could be it. Fascinated by the thought of a new challenge, Hill offered to photograph the site the next day.4

  Sure enough, the following day, Hill took his Spitfire and flew over the site. Taking low-level, oblique angled photographs on a ‘dicing’ sortie was not easy, as the oblique camera on a Spitfire was mounted below the aircraft, pointing out to the left. So the pilot, flying maybe as low as 50 feet and as fast as 300 mph, had to line himself up just to the right of the object and the tendency was for a pilot to turn on his camera after he had shot by, thus missing the target. On the day that Hill flew over the site his cameras failed, but he still got a good look at the object on the ground. He called Wavell that evening and told him that the apparatus was about ten feet in diameter and looked like ‘an electric bowl fire’ of a type that was then fairly common. From now on the photo interpreters referred to the object as ‘the bowl fire’.

  Hill’s flight had been entirely unofficial, and he prepared to fly over the site again on the following day. As he was about to leave, he was told that another three aircraft from a different squadron had been formally allocated the task of photographing the site. Not wanting to leave a task unfinished, Hill taxied over to the three aircraft and told their pilots that this particular target was his and if he found any of them within twenty miles of the location he would shoot them down. He did not explain how he could have done this without guns, but the other pilots left him to it and Hill had the place to himself.

  This time his reaction speed was just right and everything worked perfectly. The shot he took, one of the most famous aerial photographs of the war, showed the seaside villa with its unusual high-pointed roofs. And right in the middle of the picture, a short distance in front of the house down a path, was the squat bowl-like structure with a low wall around it, almost on the edge of the cliffs facing out to sea. Hill’s low-level oblique captured the radar installation in perfect detail. The date was 5 December 1941. The name of the nearest village to this mysterious site was Bruneval.

  Jones studied the photograph when it came through and realised this was different from anything else he had seen before. Claude Wavell and his team measured the installation and confirmed that it was indeed about ten feet in diameter and was situated in a shallow pit. Attached to the device itself was a small control cabin about five feet high, and the whole apparatus was capable of rotating. Because of its paraboloid shape, the bowl could tilt upwards as well as rotate horizontally. With the information about the radio waves that Jones had already picked up, he knew that the new German radar operated on a wavelength of 53 cm, with a pulse rate of about 3750 per second. Jones calculated that it must have a range of about twenty-five miles, and further deduced that it could be used to measure wi
th some accuracy the height of approaching aircraft. Thus it would complement the Freya system, which was accurate in detecting range and bearing but not height. Through a brilliant combination of Jones’s scientific investigation, Charles Frank’s alertness, the observations of Claude Wavell and his team at Medmenham, and the precision flying of Tony Hill, the British intelligence establishment had found what must be a Würzburg, the missing link in the German defensive radar network.

  Once the intelligence officers knew what they were looking for, they were able to brief the Resistance groups that were now starting to spring up across Europe. They told the Resistance agents what to search for and asked them to report back any relevant findings. So, following this first identification of a Würzburg, things began to move quickly. The Belgian Resistance reported the existence of a similar sounding apparatus just north of a German night fighter base at St Trond, thirty-five miles east of Brussels. Jones again asked for aerial photographs to be taken and when these came through he realised that this was an even larger bowl-like structure. Moreover, there were two large radar bowls and three searchlights situated around this site. Then another large site was spotted at Domburg on an island in the Scheldt estuary. Once again, Jones let Tony Hill know of this and he went out and took two more perfect low-level photographs, giving a full face and a side view of the equipment. Again there were two radar installations but this time there were no searchlights. Jones called these new structures ‘Giant Würzburgs’.