Night Raid Page 4
However, almost unimaginable progress had been made at Orford Ness and at Bawdsey in the four and a half years since Watson-Watt and Wilkins had stood in a field at Weedon and watched the cathode ray tube come alive as the old RAF bomber flew by. A network of radar stations had been set up around the eastern and southern coasts of Britain. An understanding of how to calculate range, bearing and even height had been made. Strides had taken place in the development of airborne radar. The army and the navy were now aware of the opportunities this new science offered them. But as the research scientists packed their bags and left Bawdsey, there were still questions for the rest of the scientific establishment in Britain to ponder: had the Germans developed their own radar system? Was there a German version of Bawdsey Manor also working somewhere in great secrecy? And if so, did the enemy have anything equivalent to the operational radar system now in place in Britain?
3
Freya and Würzburg
Robert Watson-Watt had been working tirelessly for more than two years on the development of radar when, in the early summer of 1937, he decided to take a holiday. He and his wife Margaret planned a walking tour in a remote part of what was then called East Prussia, the easternmost part of the German Reich. They were both interested in ecclesiastical architecture and liked Germany and the Germans. Equipped with suitable walking gear and heavy boots, along with a wooden mount and paper for his wife to sketch on, and what looked like a small pocket torch, they set off. After a few days in Berlin going to concerts and movies, they moved east and checked in to a hostel in Neukirchen. It was a remote spot. Not a single foreigner had signed the hostel register for five years.
Although Watson-Watt and his wife intended to enjoy a brief break from the demands of creating a new technology for the defence of Britain, there was rather more to their walking holiday than might be supposed. The British intelligence service, known as the Secret Intelligence Service (SIS), had picked up stories of an establishment similar to Bawdsey in the Grosses Moosbruch, a remote forested moor in eastern Germany. The SIS wanted someone to go out and see what was happening. Who better than the chief himself, who would be sure to identify anything resembling radar towers under construction?
So, under the guise of a walking holiday, Watson-Watt and his wife headed off on their spying mission. The SIS kitted him out. The ‘torch’ he took was a tiny telescope-and-microscope. Margaret made sketches not only of local churches but also of high-tension pylons. And they even had a cover story if interrogated that they were looking for the grave of a great-grandmother called Brücker – in fact the name of the German grandparents of Watson-Watt’s secretary at Bawdsey.
Watson-Watt took his spying responsibility seriously and systematically covered the region in question, walking through woods and climbing church steeples to gain good views of the local countryside. At one point he and his wife thought they were under surveillance from a man disguised as a peasant who repeatedly rode past them on a bicycle. But the man on the bicycle really was a local peasant busy on an errand. And there were no signs of any towers, for radar use or otherwise. Watson-Watt concluded that the SIS had been taken for a ride. He came home after a pleasant break and reported that there was no evidence to suggest the Germans were developing any form of radar.1
Watson-Watt’s walking holiday had significant consequences for British science. It became the established view within Britain that while this country had developed a sophisticated radar system and was in the process of integrating it into an effective command and control system for national defence, the Germans had developed no such system. When the war began the prevailing wisdom within the British establishment was still that the Germans did not have radar. Nothing could have been further from the truth.
German scientists had been aware from the late nineteenth century that when radio waves hit a metal object they bounced back. Even after Christian Hülsmeyer’s failure to interest the German navy and industry in his Telemobiloscope, other scientists and engineers had played with similar ideas during the First World War, although no progress was made in developing a practical system of radar for military use. The key figure in the next stage of radar development in Germany was a brilliant young experimental physicist named Dr Rudolf Kühnhold. He was a passionate and serious young man, sometimes impetuous and very sensitive to the impression others had of him. Kühnhold had done his postgraduate work at the University of Göttingen and was only twenty-five years old when in 1928 he joined the NVA, the Experimental Institute of Communication Systems, which was a part of the German navy in the port town of Kiel. As in Britain, the Germans were experimenting with the use of audio signals to pick up the presence of vessels at sea, and with sonar, underwater acoustics, to follow vessels below the surface. Kühnhold grew frustrated with this line of research and decided that the future lay with the electromagnetic study of radio waves rather than acoustics. In 1931, Kühnhold was appointed Scientific Director of the NVA and his appointment ushered in a new era in German science.
In Germany, the impulse to develop a system for identifying objects at a distance came not from defence, from finding an early warning of the approach of enemy bombers as in Britain, but from offence. The German navy was keen to find better ways of targeting its guns on enemy ships and to find an improved system for range finding and location, a two-dimensional problem, in contrast to Britain’s need. So Kühnhold began a series of experiments using short wave transmitters to detect the presence of vessels at sea. He started working with the Pintsch company using directional antennae. As this system was intended for use on board ship, there was no possibility of constructing 350-foot towers like those Watson-Watt and his team were to build on the Suffolk coast. Everything had to be smaller in scale, and German radar research therefore went off in an entirely different direction to the work that would follow in Britain. Instead of a system that covered a broad field of action, as it were floodlighting a large area of the sea in its search for enemy aircraft, Kühnhold developed a system that would be far more focused and directional, more like a searchlight seeking out a specific object. But he and the Pintsch company kept coming up against the problem that would dog the early development of radar. Using a wavelength of about 50 cm, he simply could not generate enough power in a transmitter to send out waves strong enough for a receiver to pick up their echoes after they had hit an object and bounced back.
Help came from an unlikely quarter. Philips, the electrical giant based in Holland, had designed a magnetron valve that could generate about 80 watts of power on a shorter wavelength of 13 cm. Using the Philips valve and a frequency amplifier in the receiver, Kühnhold devised a piece of equipment that was able to pick up vessels crossing Kiel harbour at a range of about two miles. This was still nowhere near good enough to meet the demands of the German navy for its gun sighting. Kühnhold had to think again.
Kühnhold consulted several electrical specialist firms, including Telefunken. Turning up unannounced at the office of the company’s head of development, Professor Wilhelm T. Runge, Kühnhold tried to sell the possibilities of radar, but much to his annoyance Runge was not interested. All the other firms he approached were doing valuable work for the German navy or air force and had neither the capacity nor the inclination to commit resources to this new field of experimental research. So, along with some radio specialists, Kühnhold decided to set up his own company, Gema.2 It was set up with an experimental radar outstation at Pelzerhaken in Schleswig-Holstein on the Baltic coast, to the north of Lübeck. This was another exposed and remote coastal spot so beloved of the radar pioneers. Although it was never on quite the same scale, it was the nearest the German engineers had to Orford Ness.
Although progress was slow, on 24 October 1934 tests at Kiel detected a vessel at a range of eight miles and in addition picked up a return signal from a Junkers aircraft that just happened to fly across the beam. This was four months before Watson-Watt carried out his first experiment near Daventry. But in a remarkable prefiguring o
f Air Marshal Hugh Dowding’s offer in February 1935 for the establishment of an experimental radar station in Britain, the German navy were sufficiently impressed with the results of Kühnhold’s experiments to award him a grant of approximately £10,000 for the further development of the technology.3 From now on, Kühnhold’s research was concentrated on a frequency of 600 MHz and a wavelength of 50 cm. Moreover, his research was now to continue in absolute secrecy, as in Britain.
Kühnhold realised he could concentrate the radio waves in pulses, just as Watson-Watt discovered, and by experimenting with different types of transmitters he was able to site the transmitting aerials alongside those of the receivers. He requested German industry to improve the quality of its cathode ray oscilloscopes in order to make them easier to read, so as to catch up with progress elsewhere in Europe and in the USA. Development was slow but in September 1935, new tests were at last carried out in front of senior naval officers. The tests were successful in locating the gunnery ship Bremse at a distance of about eleven miles with an accuracy in range of roughly a hundred yards. The naval officers saw that they had the makings of a superb tactical gun-aiming device and committed more funds to the research. It was decided for security reasons to disguise the work as Dezimeter Telegraphie (Decimetre Radio), or De-Te for short, and in the following year a range of further designations appeared, including Funkmessortungsgerät (Radio Locating Apparatus), abbreviated to FmG or FuMG. This was remarkably similar to the term Radio Direction Finding or RDF, invented in Britain to disguise the research work that was taking place there.
The German scientists soon realised the advantages of working at longer wavelengths and when they shifted to a 2 m radio wave they managed to extend the range of their radar. They also started to use parabolic reflectors, large bowl-shaped structures with a diameter five times the wavelength of the radio signal they were sending out. In early 1936 this new system picked up echoes from an aircraft flying over the sea at nearly twenty miles. With further improvements this was soon extended to forty miles. This became the basis of the radar the Kriegsmarine was to use during the war, known as Seetakt.
Although the German and British scientists and engineers were working in a roughly parallel direction, there were many differences between the research being carried out in Germany and in Britain. In Britain, radar developed in close liaison with the military and with the senior scientists at the Air Ministry. And Watson-Watt developed a sort of two-way dialogue with serving officers in the RAF. By contrast, Kühnhold’s work carried on without regular input from the German navy, although their funding proved vital to its continuation. The navy, and later the German air force and army, laid down the specifications they wanted the radars to adhere to and left the scientists to get on with it.
In Germany in the late 1930s a rivalry also developed between the different civilian companies that became involved. This was typical of the way the Nazi state operated. Different companies with their teams of physicists and engineers worked in isolation and in competition with others. There was little unity of purpose. And it suited the military to have one company trying to outdo another in meeting or surpassing the specifications that had been laid down. It also resulted in the splintering of the German radar establishment, which began to use different forms of the technology, operating on different wavelengths in different ways, for different military clients.
For instance, the Lorenz company, another electronics outfit, produced the Blind Landing System, a set of beams transmitted from the airfield that were used to guide an aircraft in to land during bad weather when visibility was too poor for the pilot to see the landing strip. Lorenz developed a mobile radar using parabolic reflectors that was efficient at twenty miles’ range. General Wolfgang Martini, the head of the Luftwaffe’s signals division, soon took an interest in their work and out of this association came an anti-aircraft (or flak as the Germans called it) radar that could direct the guns at overflying aircraft with great accuracy. The specifications laid down by the Luftwaffe in 1937 called for the continuous following of a target from a distance of over thirty miles to about six miles. This became known as the A2-Gerät, or A2 Apparatus.
Telefunken, the largest German electrical company of the day (which Kühnhold had approached for help in 1934), was also a leading pioneer in all forms of electronic technology. In Berlin in 1936, Telefunken had built a set of giant television cameras to transmit the Olympic Games to halls around the city. Hundreds of thousands who could not get into the main stadia could now watch the action live on giant screens. Although this was a closed circuit and not a broadcast signal, it was the first time an Olympic Games had been shown live on any sort of television.4 In what was clearly going to be a scientific war, Telefunken would be crucial to the German war machine. And so, soon after Hitler came to power, the Nazis began to extend their influence over the electronics and communications company. Telefunken’s chief executive, Emil Mayer, was expelled because of his Jewish origins and a good Nazi named Captain Schwab, who had been a U-boat commander in the Great War, was appointed to replace him. Telefunken was ordered to refocus its business away from customer-related technology and towards original research. And the objectives of this research would, of course, be dictated by the German military.
While Telefunken’s head of development, Runge, had been dismissive of Kühnhold’s radar ambitions in 1934, a year later he assembled his own apparatus, with a transmitter antenna 1 m square and a simple receiver, in order to seek out the presence of nearby aircraft. He was stunned by the strength of the returning signal he picked up. Almost single-handed he then began Telefunken’s long association with radar. Using funds earmarked for other secret projects, Runge went down the route that the other pioneers in Germany and Britain had taken. First he had to make the transmitters more powerful. This he did by directing transmissions using a parabolic reflector, which he nicknamed a Quirl. In the summer of 1936, when Watson-Watt and company at Bawdsey Manor were getting return signals from up to a hundred miles’ range, Runge and his team designed their first system, which only had a range of about three miles. It was named Darmstadt, and all future systems would be named randomly after German cities.
Step by step, Runge and the Telefunken engineers succeeded in improving all aspects of their radar. After Darmstadt came the Mainz system and then Mannheim, each with a longer range and greater accuracy than the last. Each system used the ‘searchlight’ approach, focusing its signals on a specific target area, unlike the ‘floodlight’ approach being developed at Bawdsey. This became the basis of a new anti-aircraft system in which radar guided the guns to fire on their targets. When Kühnhold heard about this research, instead of being pleased at the developments taking place, he accused Telefunken of carrying out unauthorised work on reflecting-wave technology. He was resentful of the heavyweight backing they could now bring to the experimental table. His fury was another sign of the internecine competition between pioneers that the Nazi state encouraged.
Meanwhile Kühnhold’s Gema company pursued its work on early warning systems. In November 1938, it trialled a new system that used a large rotating antenna made up of a metal grid 6 m wide by 5 m high. The receiving antenna was placed directly on top of the transmitting antenna. The operators sat in a cabin behind the antenna and the whole apparatus was easy to dismantle, move and reassemble in a new location. It operated on a wavelength of 2.5 m and had a range of 50 miles. There were three cathode ray screens on which the operators could measure the height, bearing and range of approaching aircraft with impressive accuracy. It even had a roller counter, which was like an early form of digital readout.5 This remarkable piece of technology was named Freya after an ancient Nordic goddess associated with beauty, love and fertility. It would soon prove its worth in war.
With war clouds gathering, in early 1939 the Luftwaffe laid down specifications to Telefunken for an alternative anti-aircraft system. It had to be smaller than Kühnhold’s Freya and, more importantly, it also had to be mobile
. Walter Runge designed the apparatus, which had a 3 m parabolic reflector. This was both transmitter and receiver and so obtained double the performance for half the antenna area. There was an operating cabin behind the reflector and the operators could use handles to rotate the whole device to adjust for height and bearing. In order to make it easier to move, it was designed so the bowl-like reflector could fold in half and the complete system was mounted on four wheels. It operated on yet another wavelength, 53 cm. The designers stuck a pin in the map and named it after the German city of Würzburg. In July 1939 the Würzburg A system was shown to the Luftwaffe top brass. They were hugely impressed and ordered a large number of the devices, intending to deploy them along the entire German border to intercept any hostile aircraft that dared to enter the airspace of the Reich.
Telefunken was to become a giant in electronics and communications technology, comparable only to American giants like Bell and GEC. The company went on during the war to develop ever more sophisticated radar systems and to design a system of radio telephones for the Wehrmacht. This network not only covered Germany but was extended to cover all the occupied territories from Narvik in northern Norway to Crete in the Mediterranean. When television research was abandoned because of the war, the whole television team joined the radar researchers and brought in considerable new and valuable expertise, especially in the use of cathode ray tubes. These tubes were used as the basis of all television screens until digital technology came along sixty years later.