Most Secret War

by R. V. Jones

  As regards the tactics of the campaign, it would clearly be dangerous to attack only the radar stations that could cover our intended landing area, and so we had a general rule that for every one attack that we made in the area there should be two outside it, so that the Germans should not be able to deduce from the intensity of our pre-invasion attacks exactly where the landings were to be made. Some idea of the distribution of the German radar stations may be gained from Plate 23.

  It was also important that we should be able to assess the effectiveness of our attacks as the campaign proceeded, so that we could estimate how much of the German radar cover was left intact. We had, of course, the reports of the pilots carrying out the attacks, supplemented by evidence from their camera guns. We also had a strong photographic reconnaissance effort, carried out both by regular reconnaissance pilots and by specialist units devoted to tactical reconnaissance. In addition, we could listen from stations on our south coast to the transmissions from the German radar stations themselves, to see how many of them survived. As for ground agents, we did not use them for this operation, since there was much other work for them to do.

  One vital concept of the whole campaign leading up to D-Day was that we should not only conceal our intention to land in Normandy but should also do everything possible to give the Germans the impression that we were going to land east of the Seine, so as to mislead them into keeping as much of their armoured forces there as possible and that we should then destroy all the bridges at the last moment so that they would be unable to come into action. On the night preceding D-Day, therefore, we aimed at giving the impression that a large sea-borne force was heading towards landings east of the Seine, and the development of ‘Window’ made this possible, with Robert Cockburn working out the technique with Leonard Cheshire, who was then Commanding 617 Squadron. The idea was that each of his Lancasters should fly in rectangular orbits eight miles long by two wide, moving the centre point of each orbit in a south-easterly direction at a rate of 8 knots, the speed of a sea-borne convoy. ‘Window’ would be dropped the whole time, with the Lancasters so deployed as to give the overall impression of an area sixteen miles long by fourteen wide full of ships advancing towards Fecamp on the French coast. In addition to ‘Window’ dropped by the Lancasters, ‘Moonshine’ simulators (p. 243) were to be carried on motor launches to give augmented and extended radar echoes, so that a few launches travelling under the ‘Window’ cloud would appear as a massive convoy to any airborne radar reconnaissance that the Germans might fly. A second spoof ‘convoy’ was to be created in the same way by the Stirlings of 218 Squadron, heading towards Boulogne. The scheme called for very precise flying, and it also required to be observed by at least one German radar station. It was therefore decided to leave one station intact, and the one at Fécamp was selected for this privilege.

  About three weeks before D-Day the party under Victor Tait at A.E.A.F. headquarters (housed in the famous Fighter Command premises at Bentley Priory, Stanmore) came into regular operation. On the technical side, Derek Garrard went from my Section, and on the tactical Intelligence side I selected J. A. Birtwistle, who had been a Fighter Command Intelligence Officer at R.A.F. Kenley during the Battle of Britain. The third member of my team was Rupert Cecil, an Oxford biochemistry graduate who was now a wing commander with a D.F.C. and Bar, after two tours in Bomber Command. We had met when I first lectured at the R.A.F. Staff College, and he joined me shortly afterwards. We could now see bomber operations through a pilot’s eyes, and his presence assured Bomber Command that one of their own men had the fullest access to our work. Moreover, he gave us mobility; and although his airmanship was not always conventional, I would have flown with him anywhere. In the weeks before D-Day he regularly flew us to the stations from which the radar attacks were being made. These began on 10th May, but for the first week or so I did not take a direct part, because of the other activities that we had to maintain, including setting up our own Overseas Party under Hugh Smith to go in behind the initial attack on Day D+2, to seize any radar or other technical equipment that should be sent back to England for examination.

  The evidence from the first week indicated that the attacks were going rather well, and Birtwistle—who had been briefing the pilots personally and had clearly done it excellently—told me that he thought it was time for me to come in. On his and Cecil’s advice, my first step was to visit the two main stations concerned, Thorney Island, where the radar strikes were being flown by 20 Sector, under Group Captain Gillam, and Hurn, where 22 Sector was operating under Group Captain Davoud. So on Saturday 27th May Cecil, Birtwistle and I went out to Hendon, having secured a Proctor communications aircraft with which Cecil was to fly us to Thorney Island and then on to Hurn and Odiham (from which 39 Reconnaissance Wing under Group Captain Moncrieff was flying the photographic sorties along with 35 Wing under Group Captain Donkin at Gatwick), and then back to Hendon at the end of the day.

  I had not been in the air for some considerable time, and flying with such a spirited pilot as Rupert Cecil was a new experience. As we headed south-westwards from Hendon a Spitfire from Northholt thought that he would surprise us with a dummy attack from our starboard flank, heading straight for us. From his subsequent manoeuvre I imagined that he was as surprised as I was when Cecil, with all his old bomber pilot’s reactions, banked us sharply into a turn heading directly at the fighter, at the same time shouting at the top of his voice, ‘You should always turn into an attack!’ Since I had almost forgotten the practice of going with the aircraft and was tending to use the horizon to maintain my orientation, I found myself still trying to sit vertically while we were in a vertical bank. The Spitfire duly missed us, and we went on our way, the flight itself being memorable for the sight of wild rhododendrons in bloom on the west Surrey hills—I have never been able to see them since without recalling D-Day.

  Our final approach to Thorney Island was somewhat dramatic: one moment we seemed to be high in the air and then everything seemed to happen at once, but evidently not quite rapidly enough for Cecil, who was working several controls at the same time and shouting, ‘Landing this aircraft is like delivering a bloody cow!’

  The rest of the day was uneventful (apart from a characteristic Cecil landing at Odiham which earned as big a reproach as a Flight Lieutenant Flying Control Officer dared make to a Wing Commander with two D.F.C.s, ‘I didn’t see you make an orbit, sir!’ only to be withered by Cecil’s’. ‘Didn’t you?’) until our final landing at Hendon where a Dakota was immediately ahead of us and turning into his final approach. Cecil immediately recalled one of the few rules that he observed in flying, which was that the aircraft at the lower height has the right of way. Since he could out-turn a Dakota in a Proctor, he actually turned inside the other aircraft, commenting, ‘Look at that idiot going off on a cross-country!’ and succeeded in losing enough height so that when the Dakota pilot had straightened out for his final approach he was astonished to find us immediately in front of him, and we landed amid a shower of Verey lights fired from the ground, and only just skimming the railway embankment that bordered the eastern side of the airfield. A train was travelling southwards at the time, and we were only about fifty yards in front of it—I can still recall the heads of the driver and fireman looking out and wondering whether we would miss them.

  Rupert Cecil had two other rules for flying. The first was to make sure that your radio did not work because then you could not be instructed from the ground, and in such a situation the captain of the aircraft had complete discretion in all his actions. And since some of Cecil’s actions were not exactly conventional, he had one further rule which ran, ‘You can get away with anything—once!’ And if my description of flying with him earns the disapproval of more orthodox airmen I can only repeat that I would have flown with him anywhere.

  It was a day well spent because both I and the pilots benefited from the contact. At first they had been lukewarm about shooting up radar stations, which did not explode
spectacularly as, for example, railway locomotives did; but as they came to realize the importance of the operation, they began to take a direct interest, and were perusing our ‘Rhubarb’ Appendix for themselves. Most Freyas were surrounded by blast walls (as in Figure 9, p. 213), but there had to be gaps in the walls for the operators to enter the equipment. The pilots began to study our photographs in detail and make their attacks so as to fire through the gaps. Moreover, they began to suggest the stations they would like to attack. These, of course, were decided on a central plan, and orders went out to the Sectors from Victor Tait’s party at headquarters. In particular, the station at Fécamp had been left alone, but the Typhoons at Thorney Island very much wanted to attack it. I told them that it was part of the plan that Fécamp should be left intact, and that they must do nothing unless an order came from headquarters.

  A week later we were at Thorney Island again, and it was clear from the camera gun and other photographic evidence that the attacks were being very well carried out, and exceeding anything that we could have hoped. Even before my first visit 29 sites had been attacked, involving 619 sorties, and 20 radar equipments had been badly damaged, as judged by the photographic evidence alone, and many others had probably been damaged but not badly enough to show up photographically. During the subsequent week many more attacks were carried out and I began to think that we could succeed in eliminating a substantial proportion of the German radar effort by the time D-Day arrived.

  On my visit of 3rd June I found the pilots clamouring to be allowed to tackle Fécamp, and I weighed up the arguments. If I could persuade the rest of the party at headquarters that an attack should be made, after all, and an order therefore be sent out to the Sectors, the pilots would have the satisfaction of knowing that they had had a direct influence on the conduct of the campaign. Although nothing was really necessary to boost their morale, the sense of participation would reward their enthusiasm. Also, I thought, the plan was quite possibly too rigid, in that it was all very well leaving a station alone, but it was in any event unlikely that we would eliminate all the stations that might observe our spoof convoys, and so even if Fécamp were knocked out the spoof would be duly observed by the Germans. I told the pilots that I would see what could be done, and we flew back to Hendon for the evening meeting at Stanmore. Finally I convinced the rest of the party that it was foolish not to make at least a minor effort against Fécamp: since it had not been so far attacked its radar operators were likely to be the least flustered of any in the whole coastal chain, and therefore the most likely to be able to detect that our spoof convoy was false. This argument won the day, and it was rather reluctantly agreed to send out an order to Thorney Island for a small attack to be made. The order went out on 4th June, and Birtwistle, Cecil, and I could guess at its effect.

  On Monday 5th June we again travelled to Thorney Island, and found that the pilots had just returned from the Fécamp attack. They had interpreted their orders very liberally, and had given Fécamp everything they could carry. Before returning to Stanmore, we flew on to Hurn, and it was clear that the Invasion was ‘on’ because the large armada of ships which had been in Spithead two days before was no longer there. I was silently wishing them Good Luck when we had a head-on encounter with a whole wing of American Thunderbolts. It was like standing in a butt while a covey of enormous grouse is driven past you on all sides. What was more, the Thunderbolts with their big radial engines were climbing, and so none of their pilots could see us.

  We duly landed at Hurn, my main memory there being of a Norwegian Wing Commander who had been taking part in the radar strikes, He had been shot down earlier that day, picked up out of the sea by one of our air/sea rescue launches, and had already flown another sortie. That evening at Stanmore, the meeting started with Birtwistle’s report of operations for the day, finally coming to Fécamp. He reported in respectful terms that an attack had been made that morning, and that he would give the details. As he read out the dosage, it gradually dawned on the others how they had been ‘conned’. Twenty-eight Typhoons had attacked, firing innumerable cannon shells and ninety-six 6o-lb. rockets, and dropping seven tons of bombs, many of them with delayed action. Birtwistle read out the report, and I can remember his conclusion as he came to the delayed-action bombs, looking at his watch and saying, ‘They should just be going off now, sir! Just a little raid, sir!’ The others took it very well, and we went home hoping for the best.

  Besides the German radar stations, there was another problem on my mind that night. This was whether or not the Germans would be able to jam our Gee navigational system that our Invasion craft were intending to use, and some of our vital communications links, especially those used for fighter control. My problem was that the radio listening stations operated by our own Signals Intelligence Service had taken many bearings on the German jammers, and had concluded that there were 23 independent sites, all of which would have to be eliminated. But we could only locate five sites, my own evidence being based on a dispute that we knew from Engima to have involved one of the German beam stations in 1940, when a jamming station had been sited on the same hill as it was, Mont Couple, near Boulogne. The beam station staff had been worried that the jamming station would upset their beam, but it evidently did not, for the jammer remained in position. We had thus been able to identify and locate it, and to watch its development over the next three-and-a-half years.

  From its appearance, Claude Wavell had over the years found four other stations in the Invasion and Spoof areas which he thought must all have been designed by the same architect, and which were sufficiently similar to the Mont Couple station to be classed as probable jammers; but he could find no more. Where then were the other eighteen? It is the most difficult of Intelligence problems to prove a negative case; we had all the alleged sites (which had been specified by our direction-finding operators to the nearest mile) rephotographed but Wavell and his team scanned the pictures in vain. We were inclined to think that once again the radio evidence had let us down, and that the eighteen missing stations were merely the result of erroneous bearings. There was much misgivings at A.E.A.F. when I told them to eliminate the five jammers and see what happened. Since they had been budgeting for knocking out twenty-three stations, there was effort to spare; and we told them that it would be worth using some of this effort against two further stations, including one of the Hague Peninsula which, as luck would have it, proved to be one of the main German intercept stations for listening to our own radio communications.

  As for the method of elimination, Rupert Cecil suggested that his old group, 5 Group, should undertake the job. I said I thought this was very unlikely to succeed because of the by now well established errors of night bombing. Cecil maintained that his Group could do it, and so we decided to try. On the first night, 31st May/1st June, they failed—but the photographs showed that all their bombs were concentrated in little more than a single field just to the side of the jamming site. Obviously there had been a minor marking error, and the concentration was so good that all the bombs had missed. Two nights later the Group went out again and this time the bombs completely destroyed the jammers. Incidentally, it was this that brought home to me the enormous improvement in our bombing accuracy which, if others had perhaps realized it, too, could have allowed us to revert to precision bombing earlier than we did. Anyway, the same technique was employed against the other four jamming sites, and we had no trouble whatsoever from the jammers over the whole period of D-Day and the following week. It had meant much anxious work for Claude Wavell and his staff in searching for the eighteen non-existent jammers, and we were all relieved at this vindication of their painstaking skill.

  I drove out to Stanmore on the morning of D-Day to see how things were going. Almost the first officer I met was the Group Captain who had asked me to find the jammers, and who had been very sceptical about our disbelief in the missing eighteen stations. When I asked him how the invasion was going he replied, ‘I haven’t heard, but it m
ust be going well—there is a marked increase in saluting, this morning!’

  And so it turned out. Not only had we eliminated the jammers and the headquarters of the German Signals Intelligence Service in north-west France which might otherwise have detected our movements on Day D-1, but we had knocked out a large proportion of the German radar chain. Of the 47 radar stations that were in operation three weeks before D-Day, hardly more than half a dozen were able to transmit on the vital night, and these were so shaken that their operators fell easily for Cockburn’s spoof, and German guns and searchlights were brought into action against the bogus Fécamp convoy. One operator in a station near Caen did, I believe, detect the approach of our genuine armada, but his reports were discounted higher up the chain of command because they were not confirmed by other radar stations. So we achieved a degree of surprise far greater than we could have hoped: four years’ work had proved worthwhile, although I have sometimes wondered what would have happened without that after-lunch talk with Tedder.

  Reviewing the results, Sir Trafford Leigh Mallory, the Allied Expeditionary Air Force Commander, said in his Official Despatch (London Gazette, 2 January 1947):

  The application of radio counter-measures immediately preceding the assault proved to be extraordinarily successful.… These results may be summarized as follows: the enemy did not obtain the early warning of our approach that his Radar coverage should have made possible; there is every reason to suppose that Radar controlled gunfire was interfered with; no fighter aircraft hindered our airborne operations; the enemy was confused and his troop movements were delayed.