by R. V. Jones
London 244 km 142° 10°
Sheffield 454 km 149° 11°
Bristol 372km 120° 11°
Southampton 272km 117° 11°
Birmingham 405 km 137° 11°
Homeward Flight.
The second table in the logbook ran:
Hinflug
294 10
318 11
283 11
274 11
302 11
By assuming that the entries referred to the same towns as those in the corresponding rows in the first table, and that the three-figure entries were bearings, we found that these intersected at a point near Cassel, in north France, and so could interpret the table as follows:
Objective Approach bearing from Cassel Magnetic Variation
London 294 10°
Sheffield 318 11°
Bristol 283 11°
Southampton 274 11°
Birmingham 302 11°
We could therefore deduce that:
(a) the aircraft approached its targets from the direction of Cassel.
(b) it was not concerned with distance calculations on the outward flight, which would be consistent with the distance being determined by a distant ground station, and,
(c) after it had reached its targets it intended to return direct to an aerodrome near Poix, and since it was now navigating on its own it needed to know the distance from the target back to Poix, as well as the direction.
All these deductions were consistent with what we so far knew of the Y system, and they additionally indicated that there was a ground station at Cassel similar to that on the Hague peninsula.
A third table in the log book gave us the frequencies both for the beam itself and for the ranging system employed by each of these ground stations.
Fig. 5. The method of interfering with the Y-Ranging system, January 1941. The signal re-radiated by the bomber on 46.9 Mc/s is picked up at Alexandra Palace and retransmitted back to the bomber via the television transmitter on 42.5 Mc/s
Following what I had already said in my report on the X system about the desirability of using a more subtle type of countermeasure, it was easy to see a delicious method of upsetting the ranging system: and this time I had my way. To take a specific case, the ground station at Cassel radiated a (sinusoidally modulated) signal to the aircraft on 42.5 Megacycles per second, which was picked up by the aircraft and its modulation there transferred to a transmitter on board and then reradiated back to the ground station on a frequency of 46.9 Megacycles per second (Figure 5). The ground station could then calculate the distance the aircraft was from it by the delay in the return signal. But we could pick up the signal from the aircraft on 46.9 Megacycles per second even better than its own ground station could, and we could in principle re-radiate this already re-radiated signal back to the aircraft on the same frequency, 42.5 Megacycles per second, as that being used by the ground station. This would therefore be fed in to the aircraft receiver, along with the fresh signal coming in from the ground station and in turn be fed back to the ground station again. The effect would be rather like that which occurs in public address systems where the noise from the loudspeakers impinges on the original microphone, and is therefore picked up and relayed back to the loudspeakers again. The effect on the ground station would be to make it think that the aircraft was at a false distance, because the returning waves would have travelled round an extra loop between the aircraft and our own station before getting back to their original base, and if we used a powerful transmitter ourselves the whole system would ‘ring’ just as a public address system squeals if the gain of the amplifier is made too high.
The powerful B.B.C. television transmitter at Alexandra Palace would be excellent for the task, because it worked in the right frequency band. Robert Cockburn therefore commandeered it for re-radiating the German aircraft’s own signal. It turned out that this countermeasure, known as ‘Domino’, came into use the very first night that the Luftwaffe had decided to replace KGr100 by III/KG26 because we were at last jamming the X system effectively. There had been a few minor raids by the Y-bombers during January, and the Germans hoped that they would now have this alternative formation to act as their pathfinders for the rest of the winter.
I had advised that for the first few nights we should use a minimum of power, so as to inject into the German system just enough of a signal to give them a false range, without arousing their suspicions too much. The effect was very satisfactory. One aircraft became involved in a puzzled exchange with the ground station, which informed him that he must have a wire loose in his receiver, and that he would have to abandon the use of the system for the night. Over the next few nights, we gradually turned up the power of Alexandra Palace, and the Germans realized that the system was unusable. My original objective was that, since I was not sure how long a period of success they had already had with the Y system, we should shake their confidence by making them think that we might have been interfering with it in a way that they had not detected for a period stretching some distance back into the past. This subtlety was probably unnecessary, as it happened, because we had effectively countered the system from the very first night on which it was to be used on large scale, and this by itself completely shook the German confidence.
Once the idea that we were interfering with the system became known to the German air crews, we obtained a further benefit. Since the aircraft had to be instructed by the ground station when to release its bombs, it had to be monitored all the time during its bombing run, and the ground station could handle only one aircraft at a time. The aircraft would therefore fly to a convenient area from which it could be ordered onto the beam by the ground station, and so commence its bombing run. In principle, all we needed to do was to transmit false orders to the aircraft. In fact we did not do this, but it seemed such an easy countermeasure that the German crews thought that we might, and they therefore began to be suspicious about the instructions that they received.
Coupled with the kind of misunderstanding that so often occurs in operations, it was not long before the crews found substance to their theory. On one occasion, for example, the ground station ordered an aircraft to steer a course of 270° (i.e. due west) presumably because it was east of the beam, and this was the vector required to bring it to the right point to start its bombing run. For some reason the aircraft failed to hear any further orders from the ground station and went a long way west, only to return to base and complain that the British had given him a false order. What with our real countermeasures and those imagined by the crews, Y operations became a fiasco and the system was withdrawn; we had restored our moral ascendancy for the rest of the winter.
This of course did not stop the bombing. London was such a large target that it could be attacked without any aids; and our ports, especially those in the south where the Germans could hear their beams strongly enough to give them at least the right direction of approach, were heavily attacked. But inland towns were now much more difficult; and the Germans had little further success against them.
Only later did I find that there was no foundation to our original reasoning that the Y system would involve a beam and a range measurement, correct though the conclusion was, and important as it had proved in the Battle of the Beams. The fact that it was known as Wotan had nothing to do with its method of working. Had I known enough, the Y system was code-named ‘Wotan II’; and the X system was ‘Wotan I’. And so while Wotan may have had one eye for Y, he could not have had crossed eyes for X.
We could see from vertical air photographs that the turntables for the beam transmitting aerials were made the same for the X and Y systems; and later in the war when a Y station was erected in Norway. One of our Norwegian friends photographed it (Plate 8(a)). Incidentally we called the system ‘Benito’ because we reckoned that Mussolini was the one-eyed end of the Axis.
CHAPTER TWENTY-TWO
Retrospect and Prospect
BY FEBRUARY 1941 the Battle of the Beams was as good as won. We had a
nother three months of bombing to endure, but all three major German systems, Knickebein and X and Y, were defeated. Many bombs therefore went astray, often attracted by the decoy fires that were now part of the countermeasure programme. Moreover our fore-knowledge of the German targets was at last beginning to result in the destruction of their bombers, as our nightfighters were becoming equipped with good airborne radar and as our ground controlled interception technique improved to the extent where they could now effectively hunt along the beams. With the last major raids of April and May 1941, the Luftwaffe was therefore not only tending to miss its targets, but it was beginning to encounter losses on a potentially prohibitive scale.
As information flowed in, we could see more of the Luftwaffe policy. The X-Gerät had been developed at least as early as 1937, and X-beam stations had been set up for the bombing of Warsaw in 1939, and then transferred to the Eifel region for operations against France—it was probably a French report about them that Woodward-Nutt had mentioned to me at lunch. Nevertheless the German Air Staff had not appreciated the importance of the X-Gerät until they were driven to bombing by night after the Battle of Britain, and had found Knickebein jammed. The main bombing force had been intended primarily for daytime operation, and even the X-beam flyers had been squandered in ordinary operations in the Norwegian campaign. The unexpected command of all the coast from den Helder to Brest gave the Luftwaffe an enormous geographical advantage: it could attack Britain from any direction ranging from north-east to south-west, and the situation was ideal for the beams. Fortunately, we were just beginning to parry the X-beam threat at the time that the German Air Staff realized what an important weapon their radio men had given them. The X- and Y-beam stations were then described in a contemporary Luftwaffe appreciation as ‘enormously important and hardly replaceable’, and Dr. Plendl was created a Staatsrat by Goering in recognition of his work for the beams.
Luckily for us the Germans made the classic military mistake, which we were later to repeat, of trying out devices on a small operational scale before depending on them for major efforts. It was only for this reason that I was able to unravel the beam systems in the nick of time. Since we had no technically minded agents in Germany I had foreseen in my original design for a Scientific Intelligence Service that an attack on the operational trial stage was the only one that would offer much hope of success; and this was what I did, much aided in the case of the Y system by the insight given by the Oslo Report.
So what difference had my attachment to Intelligence made? Suppose that I had not been there, or that I had agreed to Pye’s recall, or that I had accepted Eckersley’s opinion about Knickebein?—What would have happened? We should certainly have been slower with radio countermeasures, and the bombing of our inland towns must have been worse, perhaps much worse. With our nightfighters and guns powerless, radio countermeasures were our only means of defence. Not only could there have been many more Coventrys, but Milch’s aim of knocking out our aero-engine factories might have been achieved.
Scientific Intelligence was now established as a branch having its place alongside and interlocked with the more traditional divisions of Naval, Military and Air Intelligence, and we had the beginnings of a Scientific Intelligence organization. I had been able to share in the effort by the relatively small band of scientists and engineers which had affected the outcome of the Battle of Britain and the Blitz. Beyond its effect on the immediate outcome it had made a great difference to the position of science in national affairs, for it had shown the government, and indeed governments abroad, that science and engineering could be essential to national survival. The effect on Winston Churchill was profound: ‘Thus’, he wrote, ‘the three main attempts to conquer Britain after the fall of France were successfully defeated or prevented. The first was the decisive defeat of the German Air Force during July, August, and September… our second victory followed from our first. The German failure to gain command of the air prevented the cross-Channel invasion.… The third ordeal was the indiscriminate night bombing of our cities in mass attacks. This was overcome and broken by the continued skill and devotion of our fighter pilots and by the fortitude and endurance of the mass of the people, and notably the Londoners, who, together with the civil organizations which upheld them, bore the brunt. But these noble efforts in the high air and in the flaming streets would have been in vain if British science and British brains had not played the ever-memorable and decisive part which this chapter records.’ This extract comes from Their Finest Hour, of which he sent me one of his earliest copies; and in an accompanying letter he commented, ‘You certainly did “pull the crooked leg”. It makes me very proud of our country that there were minds like yours playing so keenly around the unknowable, and I am also glad that through my friendship with Lindemann I was able to bring these deadly beams into relation with the power of the British State.’
The Battle of the Beams had sorted out those of us who knew that we could rely on one another, and stand the test.
If you can keep your head when all about you
Are losing theirs and blaming it on you,
If you can trust yourself when others doubt you
But make allowance for their doubting too
Taking them in the order I met them, there was Bimbo Norman at Bletchley delving into the Enigma messages, and behind him the brilliant band of cryptographers in Hut 6, Denys Felkin with prisoner interrogation and captured documents, Rowley Scott-Farnie with the R.A.F. wireless listening service, Claude Wavell in photographic interpretation, and now Charles Frank was with me. These were among the men, to borrow my mother’s phrase, ‘who went first’.
But this was no time for mutual admiration, for the position of Britain in February 1941 was still grim. Ports were being heavily bombed. Rationing was biting hard; and any remaining amenities of peace-time life were disappearing fast. A German invasion in the summer still seemed likely, and a counter-invasion of the Continent by us extremely improbable for long into the future. Even if they did not invade, the Germans were in a commanding geographical position, with the Luftwaffe disposed in a great arc from Norway through Denmark, Holland, Belgium and France to the Spanish border. Their U-boats, operating from ports in the same great arc out into the Atlantic, were sinking more and more of our shipping; and with further ingenuity in mine design and with a more systematic mining campaign they might well strangle our ports and with them the whole island.
I used to look at my wall map every morning and wonder how we could possibly survive. Anyone in his right senses would do the best deal he could with Hitler—but we had no thought of it. Even though we were tired by the Blitz, there was that ‘white glow overpowering, sublime that ran through our island from end to end’. It can hardly be described to those who did not experience it; it must lie very deep down among human emotions, giving the individual a strange, subdued elation at facing dangers in which he may easily perish as an individual but also a subconscious knowledge that any society which has a high enough proportion of similar individuals is all the more likely to survive because of their sacrifice.
And there were some hopeful signs in February 1941. In North Africa Wavell’s Army was sweeping westwards and capturing Italians in thousands. Those of us who listened on short waves could hear generous American voices campaigning among their countrymen for help for Britain: and, relayed by the B.B.C., the strong voice of Franklin Roosevelt was saying, ‘The British and their Allies need planes and ships and tanks. From America they will receive planes and ships and tanks.’ Above all, there was the great advantage of being able to read much of the Enigma traffic. If only we could hold on, sooner or later this could turn the tide.
Much would depend on what happened in the air, and the Chief of Air Staff, Sir Charles Portal, was strengthening his organization. Intelligence was elevated to become the responsibility of a new post, the Assistant Chief of Air Staff (Intelligence) with the rank of Air Vice Marshal instead of the previous Directorate headed by an Air C
ommodore. My own position, though, did not entirely materialize as Portal and Archibald Sinclair had intended. They had secured my release from Lord Beaverbrook on the understanding that I was to be a Deputy Director of Intelligence, which would have meant a promotion of three grades over that of Senior Scientific Officer to which I had been promoted as recently as November 1940. Such dramatic elevation was too much for the Civil Service, which gave me a promotion of only one grade, to Principal Scientific Officer. This was, of course, far less rewarding, and I would have had a very good case had I pressed my claim, in view of the written commitment by the Secretary of State and the Chief of Air Staff, but it would take a long time to fight the Civil Service and in the meantime I might acquire a reputation as being a man with a grievance, which could well be fatal. So I decided not to fight, but to depend for my authority on the value of the work that I was doing, aided by the general impression that I had at any time only to go to Churchill to ask him to issue appropriate orders.
So instead of becoming a Deputy Director I became the ‘Assistant Director of Intelligence (Science)’ or ‘A.D.I. (Science)’ for short. But Assistant to whom? In Air Staff nomenclature an Assistant Director indicated a grade rather than a function, and did not imply, strictly, that I assisted a higher officer who held the post of Director. In the reorganization of Air Intelligence, Archie Boyle moved out and the new Head was Air Vice Marshal C. E. H. Medhurst, who was styled Assistant Chief of Air Staff (Intelligence). He had two Directors under him, one for Operations and the other for Security. I was made directly responsible to him and so was effectively in parallel with these two Directors, which in a way made up for the grudging manner in which the Civil Service had treated me, and I became the only civilian in an executive position on the Air Staff.
Charles Medhurst quickly sent for me, and we at once established a rapport. His last post had been as Director of Policy, but before that he had been in Intelligence and also an Attaché; I believe that he had recently been concerned with the secret deal by which Britain was allowed to use facilities in the Azores. He understood Intelligence and he was excellent to work for: if I went to him with a problem he would take immediate supporting action, and there would usually be on my desk within twenty-four hours a copy of the minute describing the action he had taken. At our first talk together he told me how impressed he had been by my work on the beams, and that he would like me to take over responsibility for analysing how the German night defences worked because he was sure that it was a problem that demanded a scientific mind.
