The crunch came in late April 1942. Aerial photography spotted that a German parachute unit had moved to a position near the head of the Cherbourg peninsula, only seventy miles across the Channel from Worth Matravers. Perhaps a German Para raid was imminent. Still the scientists were reluctant to move from their seaside home. On a visit to the site to catch up on progress with research into the pieces captured at Bruneval, R.V. Jones ostentatiously wore a revolver strapped to his belt and carried a tin hat. Throughout his visit he made it clear that he wanted to get back to London as soon as possible. His behaviour no doubt added to the scientists’ nervousness. The matter was resolved when in early May the War Cabinet instructed TRE to find a new home, its third move since leaving Bawdsey Manor at the beginning of the war. After a frantic search for alternative premises, the entire establishment was uprooted on 26 May and moved to the buildings of Malvern College in Worcestershire.
The transfer of men and materials had as many complications as the earlier moves. However, this move was its last. TRE stayed at Malvern for the rest of the war and remained there into the post-war era, when it changed its name to the Royal Radar Establishment. It was to become the centre of British radar research and the development of computers for use in guided missiles.
The capture of the radar at Bruneval had provided the final pieces the British needed in order to understand how the German defensive radar system worked. The Freyas could detect the approach of Allied bombers from about ninety miles out. As the bombers came within about twenty-five miles, the Würzburgs or Giant Würzburgs tuned in to them. With their centimetric radars they could even pick out individual aircraft flying within a formation of bombers. These installations constituted a vast defensive shield running from Denmark down through Holland, Belgium and north-eastern France, to the west of the German border. Commanded by General Josef Kammhuber, it was therefore known to the Allies as the Kammhuber Line. All bombers would have to cross this strip of territory in order to reach targets inside the Reich.
Along the Kammhuber Line the airspace was divided up into sector rectangles approximately 27 miles wide and 21 miles deep. By 1942, each sector was covered by a Freya for early warning and two Würzburgs, one of which tracked the movement of the Allied bombers while the second followed that of the intercepting German night fighters. The highly accurate information was sent back to command rooms, where two lights were shone on to a table map known as a Seeburg Table. A red light represented the movement of the bombers, a blue light that of the fighter. The controllers could then mark the angle at which to direct the fighters to target the bombers. During 1942, more and more bomber crews reported the intense activity of night fighters along the Kammhuber Line and losses were mounting.
At TRE, first in Worth Matravers and then in Malvern, a team under Robert Cockburn had been working on the jamming of enemy radar. The arrival of the stolen Würzburg parts was a huge boost to their work. They soon discovered the wavelengths to which the Würzburg could be tuned and found that it had no built-in counter to jamming.
Jones had suggested before the war, after a visit to Bawdsey Manor, that radar would always be vulnerable to what he called ‘spurious reflectors’, that is devices employed to mislead the radar receivers as to where or how extensive an approaching fleet of aircraft was. Robert Watson-Watt and his colleagues were reluctant to pursue this possibility, as they were committed to making radar work, rather than proving how it could be made not to work. As a consequence, when war came there were no plans to cope with German jamming of British radar, except the ability to switch to different frequencies.
However, the science of jamming had developed rapidly from the summer of 1940 onwards. The Royal Navy repeatedly jammed enemy naval radar stations along the French coast. The Germans had very effectively jammed British coastal radar when the Scharnhorst and Gneisenau made their dash up the Channel in February 1942. Now the British scientists had their hands on one of the most advanced pieces of German technology, they could look at different ways of jamming that too.
As well as being studied at TRE, the captured gear was also examined at the Royal Aircraft Establishment at Farnborough. Here engineers identified a weak spot in the design of the receiver. The wire from the mixer to the frequency amplifier was unshielded. If a signal was sent at the right frequency this would be picked up and would jam the Würzburg’s output. Donald Preist later described this as ‘very significant in terms of the radar war’.7
Cockburn and his team came up with a variety of suggestions. The TRE scientists realised that the Würzburg would be subject to the jamming or distortion caused by dropping dozens of strips of aluminium. They discovered that if these were roughly half the length of the wavelength of the radar, that is about 25 cm or 10 inches long and about half an inch wide, the aluminium would resonate or amplify the radio waves back to the Würzburg’s receivers. Not only would it give the impression that there were many more bombers than were actually present, it would also prevent the operators from tracking individual aircraft and so guiding the night fighters to attack them. ‘Window’ was the name given by A.P. Rowe to this jamming system. Bundles of aluminium foil were prepared and were ready for use within two months of the Bruneval raid, in April 1942. The wireless operators and flight engineers of the heavy bombers were trained in throwing the aluminium pieces out through a special chute at two-minute intervals.
However, there was a strong argument against jamming enemy radar. Once they had realised what was being done, the enemy could devise or copy similar measures to jam British radar. Watson-Watt was particularly vocal in his objection to jamming, as he believed it would ultimately lead to the disabling of Britain’s own radar systems. Churchill’s friend and scientific adviser, Professor Frederick Lindemann, also argued this view. Just before Window was going to be used for the first time, in May 1942, Lindemann obtained a prohibition. He was concerned that if the British used aluminium foil, the Germans would retaliate by using a similar method to jam British radar. Fighter Command would be unable to function, leading to a massive loss of life from German bombers attacking Britain.
Jones was totally opposed to this argument. He believed that the Germans were inventive enough to have worked out a similar form of jamming themselves. In any case, he argued, the Luftwaffe were now mostly occupied on the Eastern Front and did not pose the threat they had done against Britain in the winter of 1940–1 during the Blitz. Knowing that Window was a means to defeat the formidable defences of the Kammhuber Line, Jones wanted to use it as soon as possible. As it turned out, he was correct in predicting the Germans’ inventiveness. They tested a similar form of jamming over the Baltic, but Göring forbade its use in case the Allies retaliated with the same technique. Bizarrely, both sides had worked out the system but neither wanted to use it.
In the spring of 1942 Bomber Command launched a huge new offensive. New four-engined heavy bombers like the Halifax and the Lancaster were now available, new and more effective bombs had been designed and the Command had a new, bullish leader in Sir Arthur ‘Bomber’ Harris. He was convinced that bombing could win the war on its own by destroying the German war machine. With Stalin calling for a second front, a new bombing offensive was the only way Britain, and with it the United States, had at this point of the war of hitting back at the heartlands of German industry and wartime production. Accordingly, the first ever ‘Thousand Bomber Raid’ took place over Cologne on the night of 30 May.
Subsequently hundreds of British bombers flew almost nightly over Germany, but the losses to German night fighters and to anti-aircraft fire were alarmingly high. Various techniques were used to try to reduce the effectiveness of the Kammhuber Line. The big four-engined bombers were told to take evasive action as they passed through the Line by corkscrewing and descending a few thousand feet. This confused the Würzburg operators, who temporarily lost the bombers’ precise location. Another measure was to fly outside the Line, either to the north or the south. But such measures were short term and
limited. Jamming remained the best way to defeat the Line. Nevertheless, the delay in the use of Window continued throughout 1942. On 4 November, Air Chief Marshal Portal called a meeting to reconsider its use. But, once again, under pressure from Lindemann and Watson-Watt supported by Fighter Command, who believed they would be the big losers, the use of Window was rejected.
Instead, the RAF chiefs decided to use another jamming system called ‘Mandrel’. This was an airborne interception system carried by Defiant aircraft, which worked by creating a burst of noise that disrupted the wavelength on which the Freyas sent out their radio signals. This helped to incapacitate the Würzburgs by turning off the early warning system they relied upon. But the German engineers soon got around Mandrel by adjusting the wavelengths on which the Freyas operated. Another method, called ‘Spoof’, was also tried out in the summer of 1942. Instead of jamming the radar, this sent out radar-like pulses that told the Freyas that large fleets of enemy bombers were approaching. If these were used to distract from a real bombing raid taking place somewhere else, they could draw off the enemy fighters to the wrong area. This was used quite effectively for a few months to draw fighters away from the American daytime bombing raids. But before long the Germans installed more Freyas and were able to predict which was a Spoof attack and which was a real raid.
Everything came back to Window, but still its opponents held the floor. Finally, after most other techniques had been tried, the use of Window once more came up before the Chiefs of Staff on 23 June 1943. This time none other than the Prime Minister took the chair. Those for and those against lined up as before, and presented the same arguments as they had a year earlier. But this time the new head of Fighter Command, Air Marshal Sir Trafford Leigh Mallory, argued that even if his defences were neutralised by the German use of Window in retaliation, the case for saving the growing losses in Bomber Command was overwhelming. Mallory agreed to take responsibility for any consequences. Churchill weighed up the arguments and concluded, ‘Very well, let us open the Window!’8
There was a further delay as the Chiefs of Staff did not want to use Window before the invasion of Sicily in case it was used in turn against the landing fleet. However, Window was finally dropped for the first time on the night of 24 July 1943 in a raid on Hamburg. Its use had a spectacular effect in disabling German radar and the use of their night fighters. Only 12 bombers were lost out of 791 that took part in the raid – a loss rate of 1.5 per cent compared with 6.1 per cent for the previous six raids. On the following nights it was used in raids on Essen, and then again on Hamburg. Radio interceptors in Kent listened in to the confusion of the Würzburg operators as they struggled to identify the British bombers and guide the night fighters anywhere near them. At long last the Kammhuber Line had been blinded and the German night fighter menace muted.
The raids on Hamburg set off huge firestorms that raged across the city. Whole districts were engulfed in flames. Buildings simply disappeared. Bodies were incinerated. It was later estimated that about 42,000 people had lost their lives. More than a million had fled. Twenty-two square kilometres of the city had been razed to the ground. Albert Speer, the Minister of War Production, told Hitler that if the Allies launched similar attacks against six cities in swift succession, German war production might collapse.9 The scale of destruction unleashed by the use of Window was of a new order. But its use had been delayed for seventeen months after the stealing of the Würzburg pieces from the cliff top at Bruneval.
German scientists were of course quick to respond to jamming devices. Würzlaus was a radar system capable of distinguishing between aircraft and at least a light scattering of foil. The Germans also found ways of using weather reports across Germany to guess where the Allied bombers were heading. Combined with the monitoring of Allied radio activity, this enabled them to predict the target of a raid. Ground observers could then provide reports as the bombers crossed occupied territory and controllers could make a stab at directing fighters towards the bombing formations. Also, the German air-to-air radar interception system, known as Lichtenstein, was adapted to operate on longer wavelengths of between 3.7 and 4.1 metres, which acted as an antidote to the use of Window. German scientists also found ways of tuning in to the use of the ‘Identification Friend or Foe’ system used by the Allied bombers so that their own radar would identify the bombers as friends and not as enemy aircraft.
The electronic measures now in use in the skies over Europe were growing increasingly sophisticated. And of course, soon after counter-measures had been launched, then counter-countermeasures were developed. In the United States an immense amount of radar research was carried out at the Rad Lab in Boston, Massachusetts, where the counter-measures section had grown considerably in size. Here also, research was being done on perfecting the size and the shape of Window, known in America as ‘Chaff’, to maximise its effect. When the Americans used Chaff later in 1943, the aluminium strips were only a twentieth of an inch wide and one hundredth of an inch thick. They were even more effective in jamming the German Würzburgs. Machines for cutting the foil were built and brought to Britain. Hundreds of tons of aluminium were cut up, and in America consumers of Mars bars apparently had to do without their customary foil wrappers.
The disabling of the German ground radar defence system in the summer of 1943 was a victory of immense importance. It was the air war equivalent to the victories at El Alamein and Stalingrad, and of the defeat of the U-boat menace in the Atlantic. Like these other victories it did not bring about the immediate collapse of the enemy. But it was a turning point from which there was no going back, despite the development of counter-measures. From the end of July 1943, the RAF used Window on a regular basis. The strategic bombing offensive against Germany grew substantially. And it did so partly because the Allies had greater control over the skies through which the bombers had to fly.
Moreover, had Window and the other jamming techniques been used fifteen months earlier when they were ready for use, the lives of many aircrew would have been saved. At a conservative estimate, if the loss rate had been reduced from 6 per cent to, say, 3 per cent in the fourteen months following May 1942, approximately 1600 aircraft would not have been shot down and well over 11,000 aircrew would have been saved from death or captivity.10
We can only guess what would have happened if the Germans had in turn used their version of Window on bombing raids against Britain in 1943. Maybe more civilian lives would have been lost. Here we are entering the realm of one of the big ‘what ifs?’ of history. When the Germans did use Düppel, as they called their version of Window, briefly in January 1944, British counter-measures largely overcame its effectiveness. Certainly, the bombing of Britain by the manned aircraft of the Luftwaffe had largely run its course by then and it was not until the use of pilotless flying bombs with the V1, and ballistic missiles with the V2, from the summer of 1944 that the British people were driven back to their air raid shelters. By this stage a new generation of radar-controlled devices had been developed to help counter the V1. There was no defence against the V2. But that story belongs to another chapter of the radar war.
The Para raid at Bruneval had made a decisive contribution to the scientific war. The process of understanding how German radar technology functioned and how it could be blinded had been a long struggle. It had involved the brilliance of the photo intelligence teams in identifying the tiny specks on the French coast that proved to be radar installations; the genius of R.V. Jones in interpreting the pieces of evidence as he learnt them and in building up a detailed understanding of the German radar defence system; the heroism of John Frost and his Paras; and the skills of TRE in studying and calculating how the captured booty from the raid could be jammed.
In the autumn of 1943 Göring despaired at the success of the British radar scientists and he dismissed Kammhuber as head of the night fighter command. At one point Göring exploded with rage and frustration, proclaiming, ‘In the field of radar they must have the world’s greate
st genius. They have the geniuses and we have the nincompoops… I hate the rogues like the plague, but in one respect I am obliged to doff my cap to them.’ He ended his tirade by saying, ‘After this war is over I’m going to buy myself a British radio set, as a token of my regard for their high frequency work.’11 It was a strange but fitting tribute, marking the enormous importance of the Allied victory in the radar war.
Epilogue
Several medals were handed out as a consequence of the Bruneval raid. The Royal Navy were particularly generous and three Distinguished Service Crosses were awarded, one to Commander Cook who had led the naval operation and had taken the tiny flotilla of landing craft in to the beaches to pick up the men, and one to Lieutenant Quick who had leapt into the water to connect a line from the landing craft stuck on the beach to the adjoining ALC. Two members of the MGB crew were awarded the Distinguished Service Medal and six sailors were mentioned in dispatches.
The army was less generous with its gongs. Major John Frost and Lieutenant Euan Charteris were both awarded the Military Cross (MC). This was a great achievement and well deserved for both men. The equivalent award for other ranks, the Military Medal, went to Sergeant David Grieve, who had screamed the war cry of the Seaforth Highlanders when he successfully attacked the Stella Maris, and to Sergeant McKenzie, who had fought in the same action. Both Lieutenant Young, who had led the attack on the Würzburg itself, and Corporal Jones of the Royal Engineers were mentioned in dispatches. To everyone’s surprise, Lieutenant Vernon, the leader of the engineers, received nothing.
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