Night Raid

by Taylor Downing

  As if all this wasn’t bad enough, Taffy Bowen and his team had been forced to stop development of the vitally important airborne radar. Based at their godforsaken outpost in a hangar near Perth, they were instructed to act as manufacturers and fitters installing in Blenheim fighters the few sets that were available. Watson-Watt was reluctant to allow commercial contractors to do this. Bowen remembered this as a terrible time and began to feel frustrated and neglected. He later described it as ‘the most unpleasant and least productive’ period in his life.3

  There was an obvious need to find a new site within a few hours of Fighter Command headquarters at Bentley Priory in north London and nearer to the major industrial suppliers. This meant the south or the south-west of England. Drawing on the reconnaissance work he had done before the war, Watson-Watt suggested the answer. Rowe went to visit a site on the coast near Swanage in Dorset consisting of an expanse of flat grassland, where there was an opportunity to build a new Chain Home radar station as well as a research centre. There were airfields nearby along with a pretty, picture-postcard Dorset village. Although it was near major urban centres it was still quiet and remote, with only a few farmers as neighbours. Once again, it was an ideal location for a top secret research laboratory. As Rowe wrote, it would remain ‘in all probability, a backwater for the duration of the war’.4 The new site had the quaint Dorset name of Worth Matravers.

  It must have seemed an idyllic spot to Rowe, who spent the next few months angling to start building work and to organise the second move in less than a year. Work did not begin until January 1940, but finally the basics were ready and dozens of purpose-built wooden workshops and Nissen huts were completed. The team of 400 packed up their 140 tons of equipment once again, headed south and on 5 May 1940 opened for business. Five days later Hitler unleashed his Blitzkrieg attack upon France, Belgium and the Netherlands.

  The creation of this new unit, which came to be called the Telecommunications Research Establishment (TRE), could not have come at a worse time. Within weeks of the move, Hitler’s forces had charged through northern France, evicting the British Army at Dunkirk, and had occupied the whole of the northern French coastline. By the middle of June, France had fallen and the face of Europe had been transformed. Worth Matravers was no longer a remote backwater but was located directly across the Channel from the Nazi-occupied port of Cherbourg. The neatly laid out research station, situated right on the coast, offered a perfect target for enemy bombers or even commando raiders.

  There was discussion of yet another move, but this time Rowe dug his heels in. ‘We can do good work here and the site is popular with the staff,’ he wrote, ‘especially after our experience at Dundee.’5 He thought that another move to an unsuitable, unprepared site would cause a collapse in morale. The debate went back and forth, and it was some time before the site was given anti-aircraft defences or even machine guns to repel raiders from the sea. It was hardly an encouraging start, but Rowe’s will prevailed. The research establishment stayed put.

  The original layout of the Chain Home radar shield along the east coast had been intended to protect Britain from an attack coming from Germany. No one had foreseen that France would collapse so rapidly, and the occupation of northern France meant there was a serious lack of radar cover to the west of the Isle of Wight. A whole section of the British coast lay open to enemy attacks. After the opening of Worth Matravers there was another frantic rush to build new stations around the south-west and the Bristol Channel. Peacetime objections by conservationists were quickly set aside and, using emergency wartime powers, the Air Ministry speedily acquired land for new sites. As well as the extension of the main Chain Home system, there was a need for a new smaller type of installation called Chain Low. These were radar stations that would fill in some of the gaps between the main stations and concentrate on spotting low-flying aircraft and vessels on the sea. They had to be built on cliff tops right on the edge of the coast, ideally on headlands where there was no interference from other electrical masts or transmitters. Complete with radar towers and wooden huts to house the equipment and the staff, each site was surrounded by barbed wire and provided with an armed guard. Three of the new Bofors 40mm anti-aircraft guns were allocated to each site, although along with most things at the beginning of the war these weapons were in desperately short supply. Women were found to be particularly good at the detailed, precise work required of a radar operator and many of the new radar stations were staffed by WAAFs (members of the Women’s Auxiliary Air Force).

  Everything about RAF Fighter Command’s defensive armoury for the Battle of Britain in the summer of 1940 was a last-minute affair. The principal fighter aircraft began to appear just before war was declared. The Hawker Hurricane entered service in December 1937 and the first Supermarine Spitfires only went into operational service at RAF Duxford in August 1938. But the mass production of this fast and brilliant aircraft was mired in difficulties that proved too complex for the relatively small Southampton company of Supermarine to resolve. In early 1940, Spitfires were coming off the production line at barely forty aircraft per month.6 The Air Ministry had ordered another 450 Spitfires but there was no hope of them being delivered for months or even years to come. Meanwhile, the operational command and control system of filtering radar information and instructing pilots where to intercept enemy bombers had only recently been worked out in Fighter Command’s operations rooms. And, of course, the Chain Home radar early warning system, with all its faults and problems, had only become operational in the nick of time.

  The system now faced its first real test. By the summer of 1940 enough radar stations of sufficient quality existed around Britain to predict the arrival of fleets of enemy bombers. The key issue was one of timing. A raiding fleet of enemy bombers flying at, say, 7000 feet could probably be detected at about 80 miles. It would take about twenty minutes for those bombers to reach the English coast. It took a fighter plane like the Hurricane or the Spitfire between thirteen and fifteen minutes from being scrambled to get to a height above the incoming bombers from which it could sweep down to attack. Radar provided an early warning that gave those crucial minutes to the fighter defenders.

  But in the dogfights that followed, victory for the RAF was by no means certain. The RAF fighters were outnumbered roughly two to one by excellent German fighters like the single-engined Messerschmitt 109 and the twin-engined Me-110. The skies of southern England were soon filled with the vapour trails of aircraft in combat, as onlookers on the ground gazed up anxiously and wondered who was winning. If Hitler could command the skies above England then he would be likely to invade.

  The RAF enjoyed two strokes of good luck in the Battle of Britain. First, the Germans chose to launch their raids in the long daylight hours of summer, when the Chain Home system worked best. Although the system was still not sufficiently accurate to send RAF fighters to engage with the raiders at night, in daylight the fighters could be scrambled and directed to a point in the skies near enough to the enemy planes to visually identify and intercept them.

  Second, the Luftwaffe was not aware how effective the British radar system was in identifying their approach across the sea. On 3 August 1939, a month before war was declared, a large Zeppelin airship, the LZ 130, packed with electrical and radio listening devices, had slowly and majestically flown up the east coast of England, with the objective of monitoring and listening in to the radio waves transmitted by the strange new towers that were being built. But in a disastrous error the Germans tuned in their receiving devices to wavelengths that were too short. The Chain Home system operated at frequencies within the 22–30 MHz range, on a wavelength of about 12 m. The Zeppelin’s receivers, tuned in to much shorter wavelengths, failed as a consequence to pick up the pulses of radio waves that were being transmitted from the newly constructed towers. The conclusion passed on to Göring and the other Luftwaffe chiefs was that the British were not using radar.

  So when the Battle of Britain began, almost
a year later, the Luftwaffe did not recognise the importance of the Chain Home radar stations.7 In one aerial photograph of Bawdsey that came to light at the end of the war, a German photo interpreter had written in marker pencil ‘Not a military target.’

  In mid August, the battle between the Luftwaffe and the RAF reached its critical phase when the Luftwaffe began to attack British airfields in an attempt to destroy the RAF as a fighting force. On 12 August the Luftwaffe bombed radar stations along the Kent coast, but their defensive revetments restricted the damage and they were soon back in action. Only the station at Ventnor on the Isle of Wight suffered substantial damage and was out of action for ten days. But not realising how important these stations were to the RAF defence of Britain, Göring did not order a repeat attack. The stations carried on with their vital work day after day, predicting when and where the enemy raiders would arrive. Britain’s crucial radar ‘eyes’ were allowed to continue to watch out for the approach of enemy aircraft throughout the air battle that followed. It was an extraordinary blunder by Göring and the Luftwaffe.

  Despite the advantage that the radar network gave to the defenders, the RAF began to wilt under the pressure. The pilots and ground crews were on standby from before dawn until dusk, from about 4.30 a.m. to 9 p.m. The strain was immense. In the second half of August the Luftwaffe mounted ever heavier attacks on RAF airfields, destroying planes on the ground as well as in the air. On 18 August, the RAF lost 63 fighters destroyed with a further 62 damaged, the Luftwaffe 69 aircraft with 31 damaged. In the last week of that month the RAF lost 144 Spitfires and Hurricanes; the Luftwaffe lost a similar number of planes, but had larger reserves to draw upon. The attrition was taking its toll and Dowding realised that his supply of skilled pilots was running out. The Battle of Britain was a prelude to a German invasion. If the battle was lost, it could prove a disaster. Then Hitler announced a change of tactics.

  A group of RAF Wellington bombers had hit Berlin. Although the damage was minimal, Hitler was furious that the capital of the Reich had come under attack. He ordered the Luftwaffe to retaliate by bombing London. On the afternoon of Saturday 7 September, the radar stations picked up a huge mass of German bombers and fighters approaching the English coast. It filled a vast airspace of about eight hundred square miles. But to their amazement, the bombers flew on over the airfields they had been attacking, over the green fields of Kent, and over the suburbs of London in order to drop their bombs and incendiaries on the docks and the East End of the city. The docks, the centre of a huge trading empire, were set ablaze. As hundreds of buildings burnt, further waves of bombers arrived and dropped more bombs. Four hundred and forty-eight civilians were killed and 1500 wounded. On the next night further raiders came back to bomb the same targets. Although there were still furious dogfights to be fought between the RAF and Luftwaffe fighters, the RAF had been saved from a loss rate it could endure for not much longer as the Luftwaffe began to attack civilian and industrial targets. The people of London and the other major cities of Britain became the target. The so-called ‘Spitfire Summer’ ended with plans for invasion of southern England being put on hold.

  The triumph of the Battle of Britain was a victory for the men and women of RAF Fighter Command who had fought against a powerful enemy and had refused to give in. But it was also a victory for the men who had developed the radar system and turned it into a powerful agent for the defence of Britain. Radar really did make the difference between victory and defeat for the beleaguered country. For without radar there could have been no victory in the skies over southern England in the summer of 1940.

  The Luftwaffe continued its daytime raids sporadically into October 1940, but as autumn advanced a new phase of night bombing began, the offensive known as the Blitz. London was blitzed, with one exception, on seventy-six consecutive nights. The scientists at TRE were still having great difficulty finding a system with the necessary accuracy to guide fighters close enough to bombers at night to be able to locate and intercept them. It proved impossible to convey the detailed information from the linear, time-based displays then in use in the chain radar stations to a control room for a controller to be able to interpret all the data as if in a 3D environment quickly or accurately enough. By the time the information had been interpreted, both the fighter and the bomber had moved on. Moreover, the Airborne Interception system developed by Bowen on a wavelength of about 1.5 m was still basic. It depended on the use of dipole aerials, two aerials along the wing and fuselage of the night fighter in the shape of a T. The navigator had before him a cathode ray tube display, and by comparing the strength of the radar echo of the enemy aircraft on each of the dipoles he could give the pilot instructions to fly left or right, or to adjust his altitude up or down. Such a system was barely operational and by the end of October 1940 only one enemy bomber had been shot down with its use.8

  During the summer of 1940 a revolution took place in the presentation of information on the radar screen. A new system called the Plan Position Indicator (PPI) was tried out at TRE in which the operator looked at a round, specially treated ‘after-glow’ screen with a rotating line that picked up objects as blips. The screen represented the surrounding area, with the radar station at the centre, and every rotation of the sweeping beam highlighted the geographical position (the plan position) from the radar station of the objects being followed. PPI is supremely simple in concept and has remained the standard format for displaying radar information ever since.

  This was not the only advance made in the summer of 1940. One of the great achievements of Watson-Watt and his team was the close links they established both with the industrial partners who would manufacture the devices they created and with the universities where much original, pure scientific research was taking place. Two physicists, John Randall and Harry Boot, had spent time observing the radar towers in operation at Ventnor before the start of the war and had gone back to their university at Birmingham to try to find a way to reduce the wavelengths at which radar could operate. They set themselves a target of trying to produce a radar signal of sufficient power at 10 cm wavelength.

  It had been known from the beginning that shorter wavelengths or microwaves would be less vulnerable to jamming, and far more accurate at distance, than radio signals using longer wavelengths. The problem was to develop a transmitter that could generate the power to send out sufficiently strong microwaves, and a receiver sensitive enough to pick up the waves when they bounced back. John Randall was in his mid thirties, a tireless researcher who would not take ‘no’ for an answer. Harry Boot was in his early twenties and was less conventional, more adventurous and willing to try anything, but was also obsessed by the challenge the pair had set themselves. Looking at the various devices available they decided to work on the magnetron.

  The magnetron was a vacuum tube inside a magnetic field that was able to generate small amounts of energy of about 30 or 40 watts to power radio waves. Randall had found a book by Heinrich Hertz by chance in a second-hand bookshop while on holiday. Hertz, the great German physicist, had discovered in the 1880s that electricity could be transmitted by electromagnetic radio waves. Using the principles written up by Hertz nearly sixty years before, the scientists borrowed a couple of transformers and used a rectifier Boot built in the workshop. They began to adapt conventional magnetrons into what was called a resonant cavity magnetron. The first experiment on 21 February 1940 was a Heath Robinson affair using wax to seal the joints and a halfpenny coin to plug one end of the magnetron. It was rigged up to a car headlamp. The headlight glowed brightly and then burnt out, showing that the cavity magnetron had generated more power than anticipated. Within a few days Randall and Boot had linked their cavity magnetron to more powerful neon lights and were generating about 400 watts of energy. They measured the radio waves they were able to send out on a small antenna and found to their delight that they were transmitting powerful waves on a wavelength of 9.5 cm, only a few millimetres off their target. It was a remarkable break
through. Microwave radar technology had been born.

  Developments now followed rapidly. The crudely assembled resonant cavity magnetron that Randall and Boot had built was transferred in great secrecy to the General Electric Company laboratory in Wembley, one of the most advanced electrical labs in Britain. Here, GEC started to manufacture a new series of cavity magnetrons with proper seals and a pulsed power supply. Within weeks they were producing models that could generate 12 to 14 kilowatts (12,000 to 14,000 watts). In mid July the first of these newly manufactured cavity magnetrons arrived at TRE at Worth Matravers. A.P. Rowe allocated it to a team led by Philip Dee, who had worked alongside Rutherford at the Cavendish Laboratory at Cambridge before the war. Dee’s team included a brilliant young lecturer and research scientist who had been working on detecting cosmic ray signals at Manchester University, Bernard Lovell. Alongside him was another young luminary, Alan Hodgkin, who before the war had developed sensitive electronic equipment at Cambridge. Both men would later help to shape the face of British post-war science.9 The team soon eagerly fitted this new toy into an effective radar system and on 12 August, the very day that the Luftwaffe launched its offensive against the RAF’s radar stations, the relatively small device, mounted on a swivel, tracked an aircraft flying a few miles away down the coast.