by R. V. Jones
To set the problem in perspective, I need only quote Churchill’s minute of 8th July 1940 to Beaverbrook:
But when I look round to see how we can win the war I see that there is only one sure path. We have no Continental army which can defeat the German military power. The blockade is broken and Hitler has Asia and probably Africa to draw from. Should he be repulsed here or not try invasion, he will recoil eastward, and we have nothing to stop him. But there is one thing that will bring him back and bring him down, and that is an absolutely devastating, exterminating attack by very heavy bombers from this country upon the Nazi homeland. We must be able to overwhelm them by this means, without which I do not see a way through.
A sustained air bombardment of Germany was therefore a major instrument of military policy, all the more appealing to the nation as a whole because of the Blitz. As Churchill himself said, the almost universal cry was, ‘Give it to them back!’
The problem could be more closely defined by considering the choice of attacking by day or by night. The former would result in increased precision, so that it would be possible to attack selected objectives, such as oil plants, the destruction of which should paralyse the German military effort. But our early experiences in attacks on naval bases such as Kiel quickly showed that bombers could not defend themselves against fighters, even when flying in close formation where cross-protection between the bombers had been carefully rehearsed. Therefore if major attacks were to be made by day, these would require fighter escort, and it was easy to prove, or so it seemed, that this, too, would be bound to fail. The argument was simple: the Germans would be fighting over their own territory, and near their home bases: their fighters would therefore only need a short range, whereas ours would require a very long range: and since short range fighters have to carry far less fuel, they could therefore have a higher performance and so shoot down our long-range escort fighters. Moreover the German fighters could be under control from the ground and choose the time, place and manner of interception. All these factors were confirmed by the experience of our early raids, and so it seemed that a daylight bombing offensive against Germany would be quite impracticable. We should therefore have to attack by night, when the German fighters would be severely handicapped in finding us; and, again, our experience during the Blitz had shown that bombers had a very good chance of getting through against free-lancing fighters. The question would therefore arise sooner or later of German progress with radio and radar aids to nightfighting and also, indeed, to anti-aircraft guns. Their successes in this direction would be a major factor in determining whether or not our bombing policy would itself succeed; and the understanding of German developments in the radar field was a problem as congenial to me as the beams had been, at least in technicality if not in morality.
I therefore drew up my plan of attack. There were other Sections in Air Intelligence who would be more expert than I was myself in such details as fighter performance and armament, and such details would better be left to them. As regards anti-aircraft guns and searchlights, the work had been transferred, with the disappearance of Freddie Wintle, back to the War Office, where it became a branch of Military Intelligence. Its new Head, I was delighted to find, was ‘Gubby’ Allen, the England Cricket Captain; he was a most friendly colleague right through the war. I myself would concentrate on German radar, because I was sure that the Germans would find, as we had found ourselves, that sooner or later they would have to depend on it for nightfighting, and if I could only understand the performance and limitations of their particular equipments, this might well prove the key to understanding their whole system of night defence.
PART TWO
CHAPTER TWENTY-THREE
Freya
IN CONCENTRATING our effort against German radar, the problem was how to get at the kind of radar that the Germans would use for defending their homeland. Here the strength of their position could also be a weakness, for they would almost certainly bring some of their radar equipment forward to the Channel coast. Indeed we already knew that they had done so, and that the name of their basic equipment was Freya. So the first phase of my attack must be to find out what Freya looked like, what its radio characteristics were, and how it performed: this should at least acquaint us with German radar technique, and the necessary information should be obtainable by photographic reconnaissance and by listening for the radar transmissions.
The second phase would probably be more difficult, since the night defences of Germany were likely to lie well back from the Channel coast, perhaps in Germany itself, where we had almost no agents operating, and which would be much less accessible to photographic or radio reconnaissance. Moreover, we had very few agents operating in Holland, Belgium or France in early 1941, because as a matter of principle we had never spied on allies and consequently had no underground networks ready to operate as soon as the Germans took over the territories. It would be some time before the Resistance movements began to operate coherently, so in early 1941 the immediate attack must be on the Channel coast in the hope that what we learnt there would enable us to brief our various agencies when these were able to operate further back.
The first scratch, if not the first blood, had been drawn when we had learnt of the existence of Freya in the summer of 1940. Would aerial photography ever improve to the extent that we could see it? The first glimmerings of an answer came one day in January 1941 when Claude Wavell, now definitely established as my main contact with photographic reconnaissance, telephoned to say that there were various curiosities that he would like to show me. These were mainly photographs of beam stations, principally on the Hague peninsula, north-west of Cherbourg, where there was a Knickebein, and two X-beam stations and one Y-beam station, all of which had circular turntables. At the end he threw in another pair of stereo photographs, also of the Hague peninsula, adding that they might well signify nothing but that there was a pair of much smaller circles about 20 feet across at the edge of a field, and these had not been there some months before. They might be nothing more sinister than cattle feeding troughs or ‘cow-bins’, as he called them, but I might be interested. They were near a village, and I asked him its name. ‘Auderville,’ he replied and a bell rang loudly in my mind—for Auderville was the name of the village near which a Freya five months before had been instrumental in the sinking of H.M.S. Delight. Could these 20 foot circles be the Freya for which we had been so fruitlessly searching?
Charles Frank and I examined them in turn. We could see the shadows of some fairly tall structure, which might merely have been like a maypole, at the centre of each circle: and then Charles spotted the vital clue that the shadows were of different widths in successive photographs. Recalling that I had found the first Knickebein by a similar observation, he suggested that the different widths might be due to whatever it was rotating between exposures, so that at one instant it had been more or less end-on to the direction of the sun, and at a subsequent incident more nearly broadside-on. In fact, the difference in breadth was only about a tenth of a millimetre on the print, and it was a very fine observation; but it was positive, and I decided to ask the Photographic Reconnaissance Unit to take a low-level oblique picture of it. Although my desire to see a photograph was urgent, I told the Unit that it should exercise complete operational freedom in picking the time and the weather for the sortie. As a result, this did not occur for some days.
When it did, the pilot returned saying that I had sent him out to take a photograph of an anti-aircraft gun. A more foolhardy request it would be hard to imagine, and it was difficult to argue with him because he had been there and risked his life, and I had not. But, although I felt rather silly, I was not entirely convinced, and I examined the photograph that he had brought back. It was indeed of a light anti-aircraft gun, but it was not quite where I had specified—it was some hundred yards or so away; and there, on the very border of the picture where it was almost lost in the distortion of the gelatine was the edge of the structure that I had aske
d to be photographed, and it did look like the edge of some kind of aerial. I therefore told the Unit that I was sorry but that I would have to ask for another photograph. This time the new pilot, Flying Officer W. K. Manifould, had the two objects beautifully centred in his picture (Plate 9(c)); there was no doubt that they were radar sets. His sortie took place on 22nd February, and on the following day Claude Wavell telephoned me to say that he had the pictures and that they confirmed our suspicions. I went out to his headquarters on the morning of 24th February to collect them, returning in time for a meeting that Air Marshal Joubert had convened for that afternoon with one item only on the agenda: ‘To discuss the existence of German radar.’
The photographs were not the only evidence that I was able to take to the meeting, for we had also at last heard Freya’s radar transmissions. These should have been easier to observe than its physical appearance, for all we needed to do was to listen in the right frequency band. But despite my warning in December 1939 (p. 74) that no proper listening service existed, and despite the fact that in our search for the X-beams we had discovered the German naval radar transmissions on 80 centimetres, our Listening Service was still inadequate, and the gap had once again to be filled by individual enterprise. This came about because in early November 1940 Air Marshal Joubert, concerned that I was still single-handed, had instructed the Telecommunications Research Establishment that they must detach an officer to help me.
The first that I knew of this was when my telephone rang and a voice said, ‘This is Mr. Garrard of T.R.E. Air Marshal Joubert says that I have to come to help you!’ This was not without embarrassment for, glad as I was to have further help, Charles Frank was just joining me, and it would take some time to get any further newcomer ‘cleared’ with Security to come to work in Broadway. The best that we could do in the meantime would be to let him work in my Air Ministry office alongside Joubert’s, and this was relatively dull.
But Derek Garrard was not a man to remain inactive.… Impatient at having so little to do in my Air Ministry office, Garrard acquired a suitable radio receiver and took it in his own car down to the south coast to see if he could find the missing Freya transmissions since the official listening service had failed. In the course of a few highly profitable days, which included his getting arrested as a Fifth Columnist for his unauthorised activity in a Defended Area, he succeeded in hearing the Freya transmissions on frequencies of about 120 Megacycles a second, or 2.5 metres wavelength, and even in getting rough bearings on where they came from. Some of his bearings in fact intersected near the very equipment that we had now photographed north-west of Cherboug. It was a most valuable individual effort, and Garrard returned with his results on the very morning of Joubert’s meeting on 24th February.
So when the meeting started, I let it run on for a little to let the doubters say that they did not believe that the Germans had any radar, and then I produced both the photographs and Garrard’s bearings. Joubert looked hard at me and said, ‘How long have you had this evidence, Jones?’ He obviously suspected that I had kept it up my sleeve just to make fools of the doubters, perhaps for weeks. I pointed to the date inscribed on the sortie showing that it had been taken only two days ago. That was the end of disbelief in German radar.
So at last we knew what one type of German radar looked like; moreover, we had heard its transmissions and had heard similar transmissions coming from other stations, whose exact locations it should now be possible to determine on aerial photographs—it is always much easier to search when you know what you are looking for. We could thus find the deployment of the coastal radar chain; and although this was only one step on the way to the main German night defences, whenever these might be built up, it also had its own significance, as I pointed out to A. P. Rowe when he visited my office and we may have been showing signs of elation at our new discoveries. He commented, ‘This is all very pretty, but what good is it?’ My reply was, ‘Some day we’re going back, and we shall need to deal with those stations if we are going to land successfully.’ So we set to work to build up a complete dossier of all the German radar stations that we could find.
It was unlikely that Freya was the only type of radar equipment that the Germans had. Indeed, we knew that their naval radar was different, at least as regards the wavelength (80 centimetres) on which it operated. Moreover the Oslo Report had told us that there was another system working on about 50 centimetres with paraboloidal aerials: what had happened to it? The first glimmering of an answer came at much the same time as the Auderville photograph was taken, when we heard through Enigma that a Freya equipment was being sent to Rumania along with another equipment called ‘Würzburg’ for coastal protection, and that two Würzburg were being sent to Bulgaria for a similar purpose. Since radar equipment was not very plentiful, I assumed that these were the minimum number of equipments that would just cover the Black Sea coastlines of the two countries, 260 kilometres for Rumania and 150 kilometres for Bulgaria. Each Würzburg in Bulgaria would therefore have to cover 75 kilometres of front, which it could just do if it had an all-round range of 37.5 kilometres. If this were so, the Freya in Rumania would have to cover (260–75) kilometres, which meant that a Freya must have an all-round range of 92.5 kilometres.
We already knew from Garrard’s observations that Freyas sent out 1000 pulses per second, so that their designer was expecting to get the reflected pulses back within a thousandth of a second; and since radio waves travel with the speed of light, roughly 300,000 kilometres per second, the double journey to the target and back could not be longer than 300 kilometres, giving a range of 150 kilometres as a maximum. So the 92.5 kilometres deduced from the slender Rumanian evidence as a minimum was of the right order. This led us to hope that the equally slender evidence for the Würzburg range as 37.5, or say 40, kilometres might be good, too. And hope it was, for we had another clue which encouraged us to think that Würzburg might be the key to our major problem. This was the institution of a nightfighting area which was defined as a circle of 40 kilometres radius centred on den Helder in north-west Holland.
From what we could see of Freya, it was unlikely to be able to measure the height of aircraft, but we ourselves were already finding that for effective night interception the ground controller needed to know the height of the bomber as well as its position on the map. The Germans must encounter the same difficulty, and would therefore be tempted to use a second type of radar equipment which could measure height, and they would have to restrict their nightfighting radius to whatever range this second equipment might have. Was this the explanation of the den Helder circle, and was it more than coincidence that its radius was 40 kilometres, when we had deduced at least 37.5 for Würzburg? The paraboloidal system foreshadowed by the Oslo Report should be capable of measuring height, for in contrast to the vertical flat mattress-like aerials of Freya, the paraboloid could be tipped up as well as rotated.
So, tentatively, the key to German nightfighting would be the Würzburg apparatus, which would have a paraboloidal aerial looking like a large electric ‘bowl fire’. If Oslo were right again, its transmissions should be on a wavelength of about 50 centimetres: and, if 40 kilometres were its maximum range, its pulse repetition rate should not exceed 3750 per second. With these figures in mind, we searched and found the transmissions: their wavelengths were about 53 centimetres, and the pulse repetition rate was 3750. The first transmissions that we detected came from the Channel coast, and the obvious next step was to locate a site accurately enough for photographs to be taken. For the moment, though, this was impossible—it had been difficult enough to find the first Freya on a photograph, and Würzburg was almost certainly smaller. What I hoped was that the Germans, faced with problems of security in unfriendly territory, would try to minimize their difficulties by keeping their equipments as ‘bunched’ as possible, so that sooner or later they would decide to put Würzburgs alongside Freyas. We would therefore photograph as many Freya stations as often as we could, in the hope t
hat one day we would spot a Würzburg.
On the basis of the first Freya photograph, my relations with the photographic reconnaissance pilots were now very good. I think that they must have realized the difficulty in which I had been placed by having to ask that another of them should go out after the first pilot had said that I had sent him out to photograph an anti-aircraft gun, and they were obviously ready to undertake any task that I asked of them. I was therefore rather worried when I was told by Claude Wavell that a re-organization of Photographic Reconnaissance was occurring, and that it was to come under a new Assistant Directorate of Intelligence, A.D.I. (Photos). He was Peter Stewart, who up to that time had been running the Air Ministry War Room which among other things produced the Daily Summary of Operations. I was told that he was a man who had his own way of doing things, and much would depend on whether or not we hit it off together. I therefore called on him, half expecting trouble but, as with Medhurst, we took an immediate liking to one another. Peter was a member of Lloyd’s and belonged to a City insurance firm, and before the war he had joined the Auxiliary Air Force. In fact he had been Commanding Officer of No. 600, the City of London, Squadron; and he had an intense sense of duty and patriotism. There was a story that he had received an adverse report from an Inspecting Officer about his conduct of 600 Squadron; being adverse, this had to be shown to him for his comments. The point of criticism was that he was on too familiar terms with his junior officers, who actually called him by his Christian name; his comment was, ‘I would rather be called Peter to my face than Stuffy, Sausage or Ginger behind my back!’—the nicknames applying to Air Marshals Dowding, Gossage, and Harris.
