Most Secret War

by R. V. Jones

  Another agent who was supposed to be in contact with R.A.F. personnel reported that he had been told that a ‘Professor Ekkerley’ (whom I hoped the Germans would identify as Eckersley) had been giving special lectures to R.A.F. units in which he described the new ‘Jerry’ radio navigational system using Lorenz-type beams. I left it to my German opposite number to work out whether ‘Jerry’ stood for ‘Jay’ or for ‘German’ or for any other object with which his knowledge of English may have acquainted him. The agents were enthusiastically thanked by their German masters for their very valuable information.

  I could not know in advance whether or not the hoax would be successful, but the enthusiasm mentioned in the last paragraph was a good sign, and we might therefore hope for perhaps three months’ life for Gee once operations were started on a large scale, before the Germans were able to revise their ideas of what we were doing and develop suitable jammers. In fact large-scale Gee operations started on 8th March 1942, and no jamming was experienced until nearly five months afterwards. We had therefore obtained considerably more than the three months for which we had hoped at our most optimistic, and prisoners were still being interrogated about the Jay beams as late as July. In his book Instruments of Darkness, Alfred Price has provided further evidence because he discovered an account of a meeting in Berlin on 26th May 1942 to discuss our new navigational system. The Intelligence Officer in charge of the Intelligence investigation was Engineer-Colonel Schwenke, who reported:

  We have also carried out a systematic interrogation of prisoners. The following facts have come to light. As a result of the extensive use by us of the Knickebein and X- and Y-Gerät systems these devices fell into British hands; this was because we did not fit demolition charges.

  In mid-1940 orders were given for the immediate construction of copies of the Knickebein and a year later, in August or September 1941, these were ready for service. The British found it comparatively simple to copy the German set, as the airborne Knickebein uses the installation for (Lorenz) blind beam (airfield approach) receivers, and the British had obtained the licence for the Lorenz set before the war.… From the interrogation of prisoners, we know that this system was used under the designation ‘Julius’.

  He went on to tell how captured Gee sets now indicated that we had also developed another system, and then gave an accurate account of the genuine Gee principle. He went on to say that the Director General of Air Signals, General Martini, was going to call a conference on the question of jamming Gee, and so it seems that jammers for Gee were not even designed more than two months after we were using it on a large scale. In the meantime the Air Signals Experimental Regiment (who had operated the beam stations against us in 1940) had themselves set up listening stations to investigate the Jay beams, and I was able to report at the beginning of 1943, ‘It is pleasing to find among the personnel some of those who were previously operating the X-beams against us, so that some of our old scores against the Regiment are being wiped out.’ A final twist to the story was that when the Germans realized that they had been hoaxed they ceased to pay any attention to the Jay beams, which continued to work throughout the war, and thus provided a useful homing service for our bombers when more sophisticated aids were jammed.

  CHAPTER TWENTY-SIX

  Würzburg

  BY THE middle of 1941 we had a fair knowledge of the Freya stations in the Channel coast and we were scanning photographs of their sites in the hope that we would ultimately find evidence of a Würzburg, the smaller paraboloidal equipment whose transmissions we could hear on wavelengths around 53 centimetres. If, as we suspected, the Würzburg could determine the height as well as the plan-position of an aircraft, it could be the key to whatever system of night-fighting the Germans might develop. It turned out that the same thought had occurred to General Ernst Udet, the World War I air ace, who succeeded in the summer of 1940 in making a practice interception of a target aircraft, on the basis of information from two Würzburgs, one following the target and the other Udet himself. On 16th October 1940 a British bomber was successfully intercepted for the first time using this technique; it was probably this experience that led to the setting up of the circular nightfighting zone of 40 kilometres radius at den Helder.

  In September 1941 we heard of another nightfighter circle, this time of 60 kilometres radius, centred near Bad Kreuznach, the wine capital of the Nahe region. Had the range of the Würzburg been extended and, if so, how? I asked for photographic cover, and was advised by Claude Wavell that it would be well if I visited Benson and met Geoffrey Tuttle, the Commanding Officer of the Photographic Reconnaissance Unit because he liked to know the reasons why he was asked to risk his pilots. I felt much sympathy, for it was too easy to ask for photographs without thinking of the risks that had to be run to get them. I readily went to Benson, and the meeting with Tuttle resulted in a lifelong friendship. He had the embarrassing and difficult task of taking over from Sidney Cotton, who he thought was the greatest leader he had ever met; but he himself set a splendid example, and he was able to call on the most able pilots in the R.A.F. to join his unit. Somehow we never found the Kreuznach station, although the area was carefully photographed; perhaps the station had not been set up, or we had insufficient idea of what we were looking for. But the disappointment had its compensation in the even warmer contact with the pilots that resulted from my visit.

  Had I known it, a photograph was already in my hands. It had come into Air Intelligence through our American liaison and had been taken in May 1941 by the American Embassy in Berlin. It showed an object on the Flak Tower in the Tiergarten (Plate 13(a)). The photograph took some months to reach me, and it was indistinct; moreover there was no indication of its scale. At first I thought it was a searchlight with some sort of control box mounted on its back, and I could only keep it in mind as an unsolved problem. Enlightenment came in an unexpected and literally roundabout way from a Chinese physicist who had worked in Berlin and was on his way back with his wife to China via Ankara. There our enterprising Naval Attaché met him, and persuaded him to come back to England in case he might have useful information. When he and his wife arrived they were most discourteously treated by M.I.5, who failed to appreciate that they had made the long and risky detour simply to help us.

  The two were locked up and stripped, and the physicist was very justifiably indignant. All his papers and suitcases had been gone through without his permission—he had been bright enough to place threads in tell-tale positions to show if anything had been disturbed. When I met him he was literally ‘hopping mad’. He was so angry that he could not keep both his feet on the ground at the same time, saying, ‘They have no right to do this to me! I am an individual man! Individual man!’ It was indeed appalling treatment for a pair who had made the relatively dangerous journey from Ankara to England instead of going directly back to China, and it was not easy to change his frame of mind. However, in the course of a day or so I managed to make a few amends on the part of His Majesty’s Government, and we discussed what the Chinese physicist had seen during his years in Berlin. I had with me the photograph of the object in the Tiergarten and asked him whether he had seen it. He had. I then asked him whether the ‘bowl’ was solid, and bright like a searchlight mirror viewed from the front, or whether the bowl consisted of a mesh more like a sieve or colander. He told me that he was not sure, but he thought that it was a mesh. If so, it could not be a searchlight, and might well be radar equipment and by that time I knew that P.R.U. was flying sorties over Berlin. I therefore asked Claude Wavell to send me some photographs, and I was able to relate the dimensions of the tower to those of the Tiergarten as a whole, which gave me the scale of the photograph and showed that the diameter of the reflector must be about twenty feet.

  Such a diameter would make the apparatus at least as large as a Freya and it should therefore have been visible on photographs of the Channel radar stations, had it been there. So the mystery of Würzburg was not yet solved. But at about the sam
e time in the autumn of 1941 Charles Frank made the vital observation that was ultimately to clear everything up. Claude Wavell had sent us photographs of the Freya station at Cap d’Antifer, the chalk headland about 20 kilometres north of le Havre. There were two Freyas situated at the top of the four hundred foot cliff, and a track appeared to run southwards from them for some hundreds of yards to a large villa further along the cliff and nearer the village of Bruneval.

  The inference was that this was the headquarters of the radar station and the track had been worn by traffic between the house and the Freyas. At least, that is what most observers would have deduced; but Charles pointed out that the track did not run quite up to the house but ended in a loop rather further away from the house than it should have done had the vehicles been driven up to it. By the loop there was a small speck which was so indistinct that we had to look on several photographs to check that it was not simply a speck of dust on the negative. Photograph No. 10(a) shows, not the photograph on which Charles made the observation, but one which was a good deal better and taken from low altitude—and even then the speck is barely visible. I requested a photographic sortie at low level, as usual giving complete operational freedom for the sortie to take place only when conditions were favourable. In the meantime I told Claude Wavell what I had done, so that he could look out for the photographs when they were taken, along with my suspicion that the object might well turn out to look like a large electric bowl fire.

  A few days later two pilots from the Photographic Reconnaissance Unit, Gordon Hughes and Tony Hill, happened to visit Wavell, who told them of my interest in the object. Tony Hill said that he would go and have a look: I had already heard of him, although not by name, as a photographic pilot who was practising most assiduously at taking low oblique photographs but was almost always missing his target. His enthusiasm never wavered, and he just went on trying.

  Later, when I came to know him well, he told me that his trouble was that he was ‘a bit slow’ in his personal reaction time, with the result that by the time he had pressed the shutter the object was past the camera. Actually, it was a very difficult thing to get right because no one had worked out properly how low oblique photographs should be taken. The only arrangement that had been made was for a camera to be pointed sideways and looking somewhat aft from the fuselage of a Spitfire just behind the pilot’s seat (Plate 14(c)). Therefore what a pilot had to do was dive and fly past the object to be photographed; the object would disappear under his wing, and he had to guess when it would reappear behind the wing and fire the shutter accordingly. Since all this had to take place while he was flying at fifty feet and three hundred miles an hour, with quite possibly a light anti-aircraft gun firing at him, it is not surprising that he found it difficult.

  It turned out that Tony Hill’s father, Colonel Hill, ran Fordham’s Brewery in Hertfordshire which had brewed the beer for the 1937 Coronation, and Hugo Meynell had been one of the Brewery’s pupils. Tony Hill himself was my idea of every schoolboy’s hero—modest, lively, and ready to go on trying indefinitely until he got things right. Actually things did not go right on his first sortie against our object—his camera failed. But he returned and telephoned Claude Wavell, telling him to tell me that he had seen the object and it looked just like what I had expected, a large bowl fire. He would go out again tomorrow and get me a photograph.

  All this was completely unofficial. Although I had formally requested a sortie, this had been allocated to another Squadron based at the same airfield, Benson, and they had decided to send three aircraft on the very same morning that Tony Hill was making his second unofficial attempt. As he climbed into his Spitfire he was told that the other aircraft were taking off for the same target, whereupon he taxied over to the other Squadron and told them that if he found any of them within twenty miles of the target he would shoot them down. As a result he had a free run; this time his camera worked—and in contrast to so many of his practice efforts he had the Würzburg almost exactly in the middle of his two photographs. They became classics; they are reproduced as Plate II. They led to the Bruneval Raid, as the following chapter describes.

  What was already clear was that whatever electronic apparatus would give a range of 40 kilometres in a paraboloid of 10 feet diameter should be able to give at least 60 kilometres range in the 20 or so feet diameter of the paraboloid of the Berlin Tiergarten provided that the pulse repetition rate was dropped from 3,750 to 2,500 per second or less, to give the pulses time to return from the longer range.

  Our bombers had for some months been reporting the existence of a great belt of searchlights along the western frontiers of Germany, and our pilots believed that these were controlled by radar. As the next phase of our attack, now that underground movements were being organized in the Occupied countries, we could brief them to look for such installations as Freyas in the hope that their presence would be reported by friendly Resistance workers. Pre-eminent among these at this stage were the Belgians. My contact with them was through Major Jempson, our Belgian liaison and, I believe, a former policeman. He had a rather flamboyant manner—I can recall him saying, ‘Tell me what you want,’ and then, with a wave of his hand, ‘I will get you anything!’ For a time I thought that this was an idle boast, but events were to show that there was substance to it.

  In February 1942 he produced for me a report of an object which, from its description, seemed to be a Freya about 5 kilometres north of the German nightfighter airfield at St. Trond and about 35 miles east of Brussels.

  Now that we had a pinpoint I could ask for a photographic reconnaissance, and the result was sent up to me from Medmenham by Claude Wavell, saying that besides a Freya there was a tower-like object on the photograph which he had not seen before. When I looked myself, I realized that he had been misled by the low angle of the sun, and that when one allowed for this the object was almost certainly a large open-work paraboloid just like the one in the Berlin Tiergarten. It was in fact what the Germans called a ‘Würzburg Riese’ (Giant Würzburg) and I was so impressed with it that I represented it on our map by a gold-headed pin.

  Moreover, there were three searchlight emplacements around it, and a later photograph showed that there was also another Giant Würzburg, this time with no searchlights, and a Freya on the site.

  It was not long before we found another station, but with two Giant Würzburgs at Domburg on the Island of Walcheren in the Scheldt Estuary. This second station was well placed for a low-level photographic reconnaissance and I let Tony Hill know that I was initiating an official request for a sortie, so that he could make sure of getting it. Once again, as at Bruneval, he came back with just two photographs, giving full face and side views of the new equipment (Plate 13(b) and (c)). Plate 13(d) also shows a photograph of another Giant Würzburg taken by a Belgian Resistance worker.

  The Domburg station had one Freya and two Giant Würzburgs, but no searchlights. At this point I became involved in an argument with our own radar experts as to how the German system worked. Our own philosophy had been to control night interceptions by means of a single radar equipment, which rotated continuously, with its information displayed on a circular cathode ray screen in which the position of the radar set itself was represented at the centre. Returning echoes were displayed along the radius that corresponded to the direction in which the radar set was ‘looking’. The result was a map showing the returning echoes as luminous points which indicated the position of any aircraft within range. This device, which was so simple and obvious that we believed that anyone could have invented it, was known as the ‘Plan Position Indicator’ or ‘P.P.I.’. Both the bomber and the intercepting fighter would show up as luminous points, and the task of the ground controller was to estimate the bomber’s course and so direct the fighter on to its tail, assuming, of course, that information was also available about the heights of the two aircraft.

  One great merit of the system was that the mapping did not need to be absolutely accurate—if, for exampl
e, the bomber were misrepresented (owing to errors in direction finding) as 5 degrees to the left of where it really was, so would be the fighter; when the controller steered the latter into the same position on the screen as the bomber, the interception might occur somewhere different from where he believed it to be, but it would still occur, which was the main object of the whole system. Thus our system automatically cancelled out any errors in locating the bomber, and we did not need to know exactly where it was. To make a radar set accurately enough to avoid these directional errors would have been much more trouble, for which no effective return could have been derived. Our system therefore depended on relative measurements of the position of the fighter with respect to the bomber, and not on absolutely accurate independent measurements on each aircraft.

  Our experts therefore could not believe it when I said that I thought that the reason for their being two Giant Würzburgs at a single German station was that one was intended to follow the bomber and the other the fighter, and that somehow the plots from the two separate instruments were married together so that the controller could direct the fighter towards an interception. Our experts thought that the second Giant Würzburg was to act as reserve in case the first broke down. I pointed out that in that case it was hard to see the reason why one of the two Giant Würzburgs in the searchlight belt always had three search-lights around it and the other none, because if the second had been a reserve, duplicating exactly the functions of the first, it should have had searchlights as well. Moreover, it was hard to believe that the Germans were so well stocked with such elaborate equipments that every night-fighter control station should have had a spare Würzburg.