by R. V. Jones
‘Window’ was still having its effect, so much so that on 8th October 1943 Goering had conceded us his admiration:
In the field of radar they must have the world’s greatest genius.
They have the geniuses and we have the nincompoops.… The British would never have dared use the metal foil here if they had not worked out one hundred per cent what the antidote is. I hate the rogues like the plague, but in one respect I am obliged to doff my cap to them. After this war’s over I’m going to buy myself a British radio set, as a token of my regard for their high frequency work. Then at last I’ll have the luxury of owning something that has always worked.
(Irving, The Rise and Fall of the Luftwaffe, p. 247).
In the ensuing turmoil, Kammhuber was removed from the night-fighter command, and was replaced by General ‘Beppo’ Schmid, who had been a Nazi in the 1923 ‘Putsch’. This was a good sign for I had reckoned that if we could get Kammhuber the sack, it was a criterion that we were winning. On the personal side, I was sorry to see him go because I had much admired the objectivity of his claims.
Our losses remained reasonably low in October (3.9 per cent) and November (3.6 per cent), and we were, of course, supplementing ‘Window’ by other countermeasures, including some against the ‘running commentary’ which the German controllers were broadcasting to their nightfighters. One of the best of our efforts was on 17th November when, during an attack on Ludwigshafen, we succeeded in counterfeiting the controller’s voice over a powerful transmitter of our own (known as ‘Aspidistra’ because it was the biggest in the world) and warning all German nightfighters to land because of the danger of fog. When the Germans found that we were intervening in this way, they substituted women for men to broadcast the commentary, but for this we were ready and had German-speaking WAAFs standing by. The next move by the Germans was to have a man repeat any orders that our WAAF gave, so that the nightfighters would know that these orders were spurious. All we then had to do was to have our man repeat any orders that their woman gave. As a further twist, they supplemented verbal orders with music, so that, for example, a waltz meant that the bombers were in the Munich area, jazz meant Berlin, and so forth, with the end of an attack being signalled by the March ‘Alte Kamaraden’.
Since this chapter is primarily concerned with bomber losses, there is a point unconnected with Intelligence which nevertheless deserves to be told. The question to be decided was whether we should fit de-icing equipment to our bombers or not. At first sight it would seem that the fitting of de-icing equipment was bound to save aircraft but the matter was put to Professor George Temple. When he looked at the figures he came to the following conclusion: the weight of the de-icing equipment meant that each bomber fitted with it must carry a smaller bomb load. Therefore, to achieve the same weight of bombs within destructive range of the target, the total force would have to be increased. Knowing the rate of casualties inflicted by the German defences on our bombers, he could work out how many more bombers would be shot down than before. This number turned out to be significantly greater than the number of bombers that, on average, would be saved by de-icing equipment. Therefore the fitting of this equipment would have increased bomber casualties rather than saved them. This is an example of a phenomenon where an action can have the opposite effect than that intended, and a lesson always to be borne in mind by politicians and administrators.
With the onset of the Battle of Berlin in November 1943, our losses began to rise. This was hardly surprising in view of the great distance over which our bombers had to run the gauntlet of the German night-fighters, but at the end of December 1943 there was a very disturbing development. My personal attention was, of course, divided between supporting Bomber Command and elucidating the details of the flying bomb, but it was through this division of attention that the trouble came to light. The watch that I had set on the 14th and 15th Companies of the Air Signals Experimental Regiment had already told us that the 14th Company was plotting the flying bomb trials. Now it showed us that the 15th Company too, was engaged in something unusual.
I was telephoned by Scott-Farnie to ask what I made of the messages that the 15th Company was sending. Once again, they were ranges and bearings, and I told him that I would look at the evidence that night, 5th January 1944. The messages referred to ‘Flammen’ (flames), and they were unusual in that they gave ranges up to 350 kilometres, well beyond normal radar range. The ‘flames’ could be switched off, and were not under the control of the observing station, which seemed to find it easier to determine range rather than bearing. They could also sometimes be seen during the day, and from the positions of the few plotting stations we were able to locate, we realized they referred to the positions of our bombers. By a process of elimination, I was quickly able to argue that the Germans were ‘challenging’ and plotting the I.F.F. (Indentification Friend or Foe) sets that had been kept switched on in some of our bombers, and perhaps also in American aircraft, too.
This was the very danger about which I had warned so strongly in 1941, and which had been dismissed by Bomber Command. My note of 12th September 1941 had said, ‘Therefore, either I.F.F. has no effect, or it contributes to our losses: we should refrain from the use of this treacherous device over enemy territory’. A year later, the Operational Research Section of Bomber Command had reported that the intervening experience over Germany had shown, ‘There is no evidence that the use of the J-Switch (by which the I.F.F. was left switched permanently on) has had any appreciable effects on searchlights, flak defences, or the activities of enemy fighters, or the “missing” rate’. The O.R.S.B.C. report had then gone on to make a fatal recommendation, all the more reprehensible for the clear warning of potential danger that I had given: ‘It is known, however, that many crews think the device effective, and it should therefore be retained.… Since no evidence has come to light indicating the harmful effects of the J-Switch, the psychological effects on the crew alone is sufficient to justify its retention’.
What this meant was that in 1942 there was no sign that the Germans were utilizing our I.F.F. transmissions. This conclusion was doubtless correct, but its implication was that although it was of no use, it encouraged crews to press home attacks in defended areas where the flak was so intense that they might otherwise have stopped short. Now, in assessing the position fifteen months later, I had to be careful because my opposition to the I.F.F. legend was well known, and my interpretation of the evidence regarding ‘Flames’ might thereby be discounted unless the proof was complete. Two days later, I issued a formal report which concluded:
It appears inescapable that I.F.F. has betrayed some of our bombers. The legend about effect of I.F.F. on searchlights may now be reaping a tragic harvest, and future tragedies of similar type will only be avoided by the peremptory application of common sense to shatter quasi-scientific superstition.
While their Radar remains neutralized, the Germans will probably make every effort to utilize the radiations from our aircraft. In view of the encouragement which they must thereby have received, they will probably try other radiations should we now thwart them on I.F.F., and we shall therefore need to be even more circumspect than before in our use of all radio equipment which involved continual transmissions from our aircraft.
At first there was some disbelief in Bomber Command headquarters, which I had accused of the immoral practice of encouraging brave men to clutch at false straws in their hour of greatest danger (I actually used these words at a conference) and I was particularly critical of the Operational Research Section which, as scientists, should have been much more objective. I was able to point to actual raids during December where, according to the Germans’ own (Enigma) reports 9 out of the 41 aircraft lost on 2nd/3rd December against Berlin had been shot down because of their use of I.F.F., 4 out of 24 lost on Leipzig on the following night and 6 out of 26 on Berlin on 16/17th December—and these may have been due to one plotting station alone. This crucial evidence was a marvellous bonus from ou
r attempts to follow the flying bomb trials. I felt that we had achieved one of the best ‘right and lefts’ of all time by picking out the 14th and 15th Companies.
At last Bomber Command headquarters was sufficiently convinced to issue orders that I.F.F. should be switched off, and I was told that the Commander-in-Chief had sent a signal to all units flaying ‘those idiots who believe in the joss-like protection of I.F.F.’. Nevertheless it proved difficult to enforce I.F.F. silence in all aircraft, and with our concentration tactics, it only needed one aircraft to leave its I.F.F. on for the whole bomber stream to be betrayed. Moreover, the ‘flames’ plotting was completely immune to ‘Window’, because of the different wavelength and because, as in the Y-system, the aircraft itself amplified the echo many times over that normally associated with radar and it positively identified itself as British.
Since I had to continue to report the I.F.F. activity for some weeks after the prohibition order had gone out, the Air Staff decided that the strongest representations should be made to the Command, and the Commander-in-Chief was called by the Secretary of State, Archibald Sinclair, to explain what he was doing. In the meantime, thanks partly to the treacherous ‘flames’ our losses had risen to more than 6 per cent in January 1944, and 7 per cent in February, and even nearly 10 per cent on bad nights.
Fortunately, at the same time as our losses to nightfighters were rising in the early months of 1944, the Eighth Air Force entered a new phase of effectiveness. The reason was the advent of the P51B, the ‘Mustang’ fighter. This aircraft resulted from a request from the Royal Air Force to North American Aviation, who built the prototype in 1940. More than six hundred had been supplied to the Royal Air Force by the end of 1941 but in their original form they were under-powered, with their Allison engines giving 1,150 h.p. Five aircraft were therefore fitted with Merlin 61 engines, and the production line was accordingly modified in America, with American-built Packard Merlins. These changed the performance of the aircraft from 366 m.p.h. at fifteen thousand feet to 425 m.p.h. at the same height, and 455 m.p.h. at thirty thousand feet. Moreover by adding extra fuel tanks that could be jettisoned, the operating range could be extended to more than 700 miles, and the Mustang could outperform all the standard German day fighters. Almost by accident the philosophically impossible had been achieved.
The result was that the American day raids could now have effective fighter escorts over a very large part of German territory. This completely changed the balance of air power, and in February 1944 the Army Air Force staged its Big Week, where immense damage was done to the German aircraft industry, including the destruction of 700 completed Messerschmidt 109s; moreover, the production of JU88s for nightfighting had been cut from 365 to less than 200 per month (Irving, The Rise and Fall of the Luftwaffe, p. 270). Despite this damage, however, overall aircraft production had risen to more than fifteen hundred per month compared with an average of about one hundred a month in 1943. But while aircraft could be produced and replaced, skilled pilots could not; and especially after the Mustangs were allowed to seek out the German fighters rather than merely escort their bombers, the end of the German fighter force was in sight.
In the meantime, though, the German nightfighters were by no means finished as regards Bomber Command. A new airborne radar set, Lichtenstein SN2 had been produced, and I reported its appearance in service during February 1944. I presumed that it was developed from the ‘Lichtenstein S’ which was an airborne set for detecting ships at sea, and that, if so, its radio frequency might be about 80 Megacycles per second, or a wavelength between 3 and 4 metres. This would be quite clear of our original ‘Window’ and we would need to produce strips of much greater length. The SN2 had a range of about 4 miles as compared with the 2 miles of the original Lichtenstein (type BC) of which we had been given a sample at Dyce in the previous May.
Even so, it would probably not have been of great use to the German nightfighters unless they could be guided into the bomber stream by some other system. Even as late as 15th February, more than six weeks after I had originally warned about the German exploitation of I.F.F., there were still ten I.F.F. sets switched on in our bomber stream. And, as I had warned, whetted by this experience the Germans were now plotting every other transmission emanating from our bombers. The Command was appallingly indiscreet in its use of radio transmissions, far beyond anything that I—with my education from the Navy in the virtues of radio silence—had ever thought possible. And, for that matter, had not the Commander-in-Chief himself written as D.C.A.S. of the German beams in 1941, ‘They are frequently a means of giving us advance warning of the enemy’s intention. On the whole, they have therefore been of more value to us than to the German bombing effort’?
After the war, one of the German scientists working in the raid tracking organization told me that he thought that we could have had no idea of the extent to which the Germans were making use of the information that we were thus prodigally providing. I could tell him that some of us certainly knew, but we had great difficulty in making Bomber Command and even our own scientists at Malvern believe it.
As one example, there was H2S, the radar bombing aid working on a wavelength of 10 centimetres. I obtained overwhelming evidence that the Germans were plotting it (they had started as early as November 1943), and were in fact equipping their fighters with a receiver code-named ‘Naxos’ to home on to the transmissions not only from H2S but also on the kindred equipment that were being fitted to our bombers to warn them of the approach of German nightfighters. Since H2S was being switched on as soon as our bombers took off from their airfields in England, the Germans could get very early warning of a raid, and get their fighters airborne so as to be able to home on the transmissions when they came within range.
Such was the disbelief in our evidence that Watson-Watt and A. P. Rowe, the Chief Superintendent at Malvern, said that they would only accept it if they could nominate one of their own officers to see every detail of our evidence and the methods by which we had obtained it. Fortunately they nominated Philip Dee, and although I suspected that the opportunity was being taken to see whether I had some great undisclosed source, I was delighted to welcome Dee, who some weeks after he joined us told me that he himself had found that the H2S aspect was indeed partly a cover, saying, ‘I have just realized that I have been sent here as a spy!’ Again, we became very firm friends, and I can remember from those days his telling me that after the war he wanted to get back to a university because he believed that the future of Britain lay in good university education, and that we should have to rebuild after the war. Having been at Cambridge previously with Rutherford, he went to Glasgow as Professor of Natural Philosophy in 1945.
While the argument about I.F.F. and H2S had been going on, our losses had risen to an almost unsupportable point, although on some raids, thanks to good tactics by Bomber Command, they were gratifyingly low. For example on 1st March 1944 we lost only 4 aircraft out of 557 against Stuttgart and on 26th March only 9 out of 705 against Essen. But in the last attack on Berlin, on 24th March, the loss rate was 9.1 per cent, and on 30th March we sustained the greatest losses of the war, 96 aircraft failing to return from the 795 sent against Nuremberg. Martin Middlebrook has investigated this raid (The Nuremberg Raid, Allen Lane, London 1973) and ascribes the losses to a number of factors, including the clarity of the night and the persistence of condensation trails in the half moonlight, along with the use of SN2 and upward firing cannon by the nightfighters. Anthony Cave Brown in Bodyguard of Lies (Allen, London, 1976) has suggested that the target was disclosed by us to the Germans in advance, so as to build up the credibility of an agent with which we intended to play a later hoax on the Germans, ‘that was intended to save lives on D-Day’ (p. 516). I have no knowledge of any such hoax, nor do I believe that anyone else has. The simple fact is that we were so prodigal with the information that we were giving to the Germans through our transmissions from the bombers themselves that the stream could easily be located; and in
the failure of any effective diversion and in the general conditions obtaining that night, the losses were only to be expected.
Possibly we did not stress the importance of SN2 sufficiently. It showed up only rarely in the Enigma traffic in February 1944; this may be explained by the fact that at the beginning of that month only 90 out of 480 nightfighters were completely fitted with it. But as it was given first to the best nightfighter crews, its effect was greater than the simple numerical proportion. And although on 6th March I had set the establishment of the SN2 wavelength for countermeasures as one of our two most urgent problems, and even though some weeks before we had correctly guessed that its wavelength would be between 3 and 4 metres, our listening searches failed to detect it. Proof only came when American camera guns caught JU88s and ME110s fitted with SN2’s ponderous aerials, and the photographs came to us in May (Plate 18); even then its transmissions were not heard until after an SN2-fitted JU88 landed in error and intact at Woodbridge in Suffolk on 13th July.