6
On windswept Romney Marsh in Kent in 1934 an extraordinary concave concrete block 200 feet long and 25 feet high stood facing the Channel. It was one of two sound locators designed by the Army acoustics section.
Much thought and money went into the design and erection. They were then the only means of detecting hostile aircraft beyond the island shores. Unfortunately they were almost useless.
The great sound mirror with microphones along its length could, under ideal conditions and with a great deal of good fortune, give a rough bearing of an aircraft a little over eight miles away but it could not indicate height or range. Temperature variations, the noise of motor-cars, boats and birds allied to make even a bearing doubtful. Aircraft approaching at an acute angle to the reflector could hardly be heard at all.
There was therefore practically no warning of a raid on England, the number of bombers, or their direction and height, until they crossed the coast and could be plotted by the Observer Corps. The warning time was too short for fighters to be scrambled to intercept. The only alternative was to maintain standing patrols over the approaches to London, but this was impossible without many times the fighter force proposed.
The air exercises of 1934 clearly showed the weakness. Not more than two in five of the ‘hostile’ bombers were intercepted. At this time the standard Vickers Virginia bomber cruised at only 73 m.p.h. and had a full-load ceiling of 7,000 feet. When used in the final night section of the exercises head-winds reduced its speed to just over 60 m.p.h., but despite this 48 per cent of the attacking force reached their targets.
Bomb loads of aircraft were rising and a generation of planes was being developed which would fly higher and would have cruising speeds of 180 m.p.h. or more. These would allow less warning and make the task of the fighter even more difficult.
It was small wonder general opinion held that the bomber was invulnerable. This, with exaggerated claims by all the leading British and European theoreticians for the effects of aerial bombardment, presented a black outlook for R.A.F. fighter defence.
At the Air Ministry there were two men concerned with science, Mr. H. E. Wimperis, Director of Scientific Research since 1924, and Mr. A. P. Rowe, a member of his staff who was the only man in the directorate then employed wholly on armaments.
In June 1934 Rowe informally surveyed the problems of air defence by the simple method of going through the dusty Air Ministry files. Among the thousands he found only fifty-six on the subject. In a memorandum to Wimperis he stated baldly that unless science found some new method of assisting air defence any war within ten years would be lost. The warning did not go unheeded by Wimperis, who instigated a series of developments which were to revolutionise warfare.
Wimperis proposed to the Secretary of State for Air in November that a committee for the scientific survey of air defence be formed within the Air Ministry under a well-known physicist, Mr. H. T. Tizard. The suggestion was approved and the committee appointed, with Tizard as chairman, Rowe as secretary, together with Professor P. M. S. Blackett, Dr. A. V. Hill and Wimperis.
After receiving Rowe’s memorandum Wimperis decided to investigate every avenue, even to the extent—not without tongue in cheek—of the possibility of the ‘death ray’, long the amusement of fiction writers. On this he consulted Mr. (later Sir) Robert Watson-Watt, a forceful Scot who had worked for many years on high-frequency radio and atmospheric research. He was then Superintendent of the National Physical Laboratory’s Radio Research Station at Slough, Buckinghamshire.
Watson-Watt was no more enthusiastic than Wimperis about ‘death rays’ but agreed to have calculations made if only to eliminate the idea. One of the Radio Research Station staff, Mr. A. F. Wilkins, prepared figures which showed that beams of sufficient power to harm human beings and machines could not then be generated but that radio beams might be used for detection.
At the end of a final report Watson-Watt inserted a note suggesting that even if death rays could be produced the target must still be found before they could be put to use. He had ideas on the problem of detecting aircraft from his research into radio wave reflections and asked if the Air Ministry’s scientific adviser would be interested. The document was put before the Tizard Committee’s first meeting in January 1935 and they immediately requested a paper on the subject.
Watson-Watt showed in Post Office Report No. 233 of June 1932 that aircraft interfered with radio signals and re-radiated them. From this he postulated that an aircraft meeting a short-wave radio pulse would act as a radiator and reflect the signal back to the ground. The time lag measured in microseconds between the emission and reception of the reflected signal could be shown on a cathode ray tube. Thus with a suitable time base the distance of the aircraft from the radio station could be measured.
The Handley Page Heyford was the R.A.F.’s last biplane heavy bomber and its span of service covered the years 1933 to 1939. One aircraft of this type was med for the first practical demonstration of radar at Weedon near Daventry on February 26 th, 1935
The basic knowledge for these assumptions was gained as far back as 1924 from work done by E. V. (later Sir Edward) Appleton at the Radio Research Station in determining the height of the ionised area surrounding the world known as the Heaviside layer. Appleton employed radio pulses to measure the echo’s time of travel.
From calculations, again made by Wilkins, Watson-Watt produced an historic document, ‘Detection and Location of Aircraft by Radio Methods’. This was submitted to the Air Ministry on February 12th, 1935.
Wimperis was keenly interested in this shaft of light on the bleak defence horizon and requested a demonstration. He and Dowding, then Air Vice-Marshal and Air Member for Research and Development, met Watson-Watt at the Royal Aircraft Establishment, Farnborough, Hants, to discuss the matter.
Watson-Watt pointed out that equipment was nowhere near being designed. What he could justify, however, were the principle and the mathematics.
Accordingly a demonstration was arranged for February 26th. The B.B.C. short-wave overseas radio transmitter, with a power of ten kilowatts, at Daventry, Northamptonshire, was to ‘illuminate’ the target while the viewers would see the reflected signal on an improvised receiver between ten and twenty miles away. The research station produced a receiver linked to a cathode ray oscillograph, the screen of which was similar to that of a television set. In the centre of the screen was a bright green spot which it was hoped would be deflected by the radio signal reflected from an aircraft. The plane, if detected, would vary the length of line made by the deflected spot.
In the late afternoon of the 26th a caravan drawn by a Morris car left the Radio Research Station, Slough, on the Bath road and later drew up in a field near Weedon in sight of the Daventry masts. The team consisted of Watson-Watt, Wilkins, and the driver, Mr. Dyer, while the ‘examiner’ from the Air Ministry was A. P. Rowe.
A lumbering Hayford night bomber from Farnborough was briefed to fly a fixed track of twenty miles up and down the centre-line of the Daventry fifty-metre beam—a boring procedure the reason for which the crew had no idea.
The field watchers heard the aircraft, kept their eyes glued to the screen and waited. Steadily the green spot grew to an inch in length and then receded as the aircraft droned away. The range was about eight miles. To a casual onlooker the inch stub would have meant nothing, but to the five men in the caravan it showed that such a system could be made to work. Thus on a winter’s afternoon in the heart of the country a device was bom which was in large measure to decide the fate of Britain and the world. In Watson-Watt’s words, ‘Britain became once more an island’.
Rowe reported his findings to Wimperis, who pressed the Air Ministry to support further development. It says much for the foresight of some senior R.A.F. officers and the gravity of the bomber threat that the sum of £ 10,000 was allocated to the work.
To ensure security an innocuous name ‘radio direction finding’ or ‘R.D.F.’ was applied to the research programme. At the time R.D.F. conveyed a relationship with time-honoured methods of direction finding by means of a ground beacon and a receiver in the aircraft.
An R.D.F. team from the Radio Research Station was formed under Watson-Watt and a home for it was found at Orfordness on the Suffolk coast. The site was near an R.A.F. airfield on a long neck of land joined to the mainland only at its northern tip. To all intents and purposes it was an island and it was not long before the researchers acquired the title of ‘the Islanders’.
The team moved in on May 13th, 1935, to what was officially called the new Ionospheric Research Station. Laboratory transmitters and receivers were ready within a fortnight. Practical experiments were possible on June 5th, when a seventy-five-foot radio mast was completed.
The islanders’ brief was to obtain approximate continuous plan positions of aircraft at long range, approximate height and strength and a means of distinguishing friend from foe.
On June 15th the Tizard Committee visited Orfordness to inspect progress. An old Vickers Valencia was used for trials but the results were poor due to atmospherics. Some weeks earlier Watson-Watt warned Rowe that several wavelengths would be necessary to combat possible enemy radio interference and much shorter wavelengths for detecting low-flying aircraft. The problem of low-level detection still exercises defence planners of the 1960s. Watson-Watt wanted wavelengths much less than fifty metres and envisaged 200-foot-high masts to obtain maximum efficiency.
While Wilkins and Dr. Bowen, with only four assistants and a part-time help from Slough, were striving to make radar an accomplished fact changes were taking place in the committees of Whitehall which formulated scientific defence policy.
In July Mr. Baldwin, the Prime Minister, told Churchill that Lord Swinton was ‘very anxious’ for him to join the newly formed sub-Committee of Imperial Defence on Air Defence, despite strong opposition from Neville Chamberlain. Churchill, a dedicated critic of the Government’s poor defence policy, agreed to serve if he could reserve his freedom of action. He did not wish to be stifled by a privileged position. Showing unusual public spirit, Baldwin approved, subject to public discussion being avoided of secret matters dealt with by the committee.
Thus Churchill became a member of one of the most exclusive and important defence committees, which was to shape the destiny of Britain. In no other country perhaps could a situation exist where a back-bench member of Parliament and ardent critic of the Government could become privy to the nation’s most jealously guarded secrets and participate in their development.
Churchill kept his promise. While his angry voice boomed across the dangerous years warning and demanding, no whisper was heard of radar or of any other device on which the committee worked.
Churchill, however, made it a condition for his joining the Air Defence Committee that his close friend Professor Lindemann (later Lord Cherwell) should become a member of the Tizard Scientific Committee at the Air Ministry. The Prime Minister agreed. Churchill found scientific matters difficult to understand and leaned heavily on Lindemann through the years as his adviser.
Lindemann, however, had his own ideas on air defence and lost no time in putting them forward. He could see the future of radar but differed from Tizard on how it should be developed and applied. He also pressed two of his favourite projects, infra-red detection and parachute bombs for breaking up bomber formations.
One of Lindemann’s physicists at Cambridge was a brilliant young man, Professor R. V. Jones. In mid-1935 Jones was engaged in repairing a rudimentary infra-red detector invented by Commander Paul McNeil of the United States Navy. McNeil was demonstrating his gadget in England, but when it broke down resorted to the Cavendish laboratories for assistance.
When Lindemann heard of the apparatus he immediately seized upon it as a possible answer to the aircraft detection problem and introduced the subject to the Tizard Committee. His other notion concerned small bombs on parachutes connected with wire to be dropped in the path of enemy bombers. The wires would foul wings and propellers and the bombs complete their destruction. This was a completely blind alley for research on which valuable time and money were wasted.
Lindemann, after much argument, gained some support for infra-red. Heat detection could not rival radar in range, but Jones managed to get a set working on a Monospar aircraft in 1936 which could detect an aeroplane at a range of half a mile. This was an achievement but the problems were so complex that infra-red was doomed to sink into oblivion until revived by the German Army for night driving and detection in 1944.
In the Tizard Committee Lindemann and Tizard were unable to agree. Both men were brilliant scientists who trained together under Professor Nernst in Berlin. Their very brilliance and contrasting personalities led to violent differences of opinion and clashes on policy and technicalities. In August 1936 Hill and Tizard resigned in protest at the arguments. Lord Swinton, Secretary of State for Air, had the courage to reappoint the original committee a few weeks later without Lindemann, but with the addition of Professor E. V. Appleton and later of Professor T. R. Merton. The differences of opinion in the Tizard Committee could have had a serious effect on the rapid growth of radar.
The acceptance of scientists for air defence can be largely attributed to Swinton. His was the guiding genius which laid most of the solid foundations of Britain’s air rearmament and, above all, he appreciated the need for scientists not as advisers but as an integral part of the fighting machine.
One of Swinton’s first acts when he was appointed Air Minister in June 1935 was to bring three scientists into the Air Ministry to sit in on air staff deliberations. This team consisted of Tizard, who became Swinton’s personal adviser, Blackett and Hill, while Lord Rutherford took a fatherly interest.
The R.A.F. in 1935 could be likened to an old-established and highly respected company which had been selling the same line too long. It was faced with intense competition from a new and virile rival in another country which threatened to put it out of business. The only alternative to extinction was the rapid development and production of a new sales line. This arrived in the form of radar. The chairman was Swinton, managing director was Tizard and board members were Blackett and Hill. The chief engineer-cum-sales manager was Watson-Watt.
Interior of the receiver or ‘R’ hut at the Dunkirk, Kent Chain Home radar station in 1940. In the centre are the ‘observer’ and the ‘converter’, with the cathode ray tube hidden by the W.A.A.F. in the foreground. On the far wall is the telephone switchboard
While the top direction sorted itself out in London there were practical developments in radar and, only a month after the Tizard Committee’s visit of June 1935, Orfordness began to show interesting results. A record pick-up at thirty-eight miles range was made and the same plane was followed out to forty-two miles. For these trials a new and shorter wavelength of twenty-six metres was used because fifty-six metres was subject to interference from commercial wireless and atmospherics. On July 24th, while awaiting the return of a Wallace biplane which was followed out to thirty-four miles, a new echo was observed at twenty miles. From its fluctuations the ground operators inferred that the echo consisted of three aircraft. For the first time radar had identified a formation. The pilot of the Wallace confirmed that it consisted of three Hawker Hart bombers which flew on blissfully unaware that their passage had been observed by the small group in the hut at Orfordness.
Two vital problems remained apart from the need for longer range detection and these were the difficulty of indicating height and of obtaining accurate bearing. By September Wilkins had measured the height of aircraft at 7,000 feet and at fifteen miles range with an error of 1,200 feet. Direction, or bearing, was far more difficult. Watson-Watt estimated that two years would be required to provide direction finding (D.F.).
In September he reported that an aircraft had been followed out to fifty-eight miles. This shattered the calculations of the air defence Sub-Committee of the Committee of Imperial Defence, which estimated that to detect at fifty miles would take some five years’ work. On the strength of the report the committee recommended that a chain of radar stations should be built covering the coast from the Tyne to Southampton. This was just seven months after the first rough demonstration in a field at Weedon.
By this time it was clear that the facilities at Orfordness were inadequate, also the erection of radar masts was embarrassing the nearby R.A.F. station. In the late summer, Wimperis and Rowe prowled the surrounding countryside looking for an alternative site and their search narrowed to the bizarre manor house at Bawdsey which stood on the mainland seashore south of Orfordness. Local gossip suggested that the owner, Sir Guthbert Quilter, might be prepared to sell. The Tizard Committee and the Imperial Defence Committee agreed, and by February 1936 an advance party occupied one of the stately towers while the stables and outbuildings were converted into workshops.
Bawdsey itself was designated as one of the stations in the radar chain so that the scientists, instead of working in a secluded laboratory, became an integral part of the defence system. This later had a major beneficial effect on development and the rapid disposal of operational problems.
The first mast was obviously too low for obtaining the best results. The shipbuilding firm of Harland and Wolff of Belfast arranged to erect a 250-foot high lattice mast at Orfordness. It was hoped to complete it by October 1935, but due to delays in the Air Ministry Directorate of Works the mast was not up until February the following year.
A second mast was completed on March 7th, 1936. Six days later Bawdsey achieved the first location of an aircraft beyond sixty-two miles with range and direction, on a Hart flying at 15,000 feet. On the same day the Tizard Committee recommended that Watson-Watt be transferred from the Department of Scientific and Industrial Research (which controlled the Radio Research Station) to the Air Ministry.
Work continued through the summer, although plagued by various snags. During these months a workable radar direction-finding system was evolved by stacking up to six directional aerials arranged on the four points of the compass and working on a six-metre wavelength. A simple goniometer was used at the base, hand rotated, and working in a similar manner to an aircraft-direction-finding loop. With a loop the signal might be coming from one direction or from exactly the opposite direction, but at Bawdsey this ambiguity was overcome by specially sensing the relays in the circuit.
The R.A.F.’s faith in its device was maintained despite slow progress. In the top level reshuffle of 1936 when Lord Dowding became the first commander-in-chief of Fighter Command, Sir Wilfred Freeman took Dowding’s place on the Air Council as air member for research and development and radar continued to be accorded the highest priority.
Squadron Leader Raymond Hart (later Air Marshal Sir Raymond Hart) was posted to Bawdsey in July 1936 as the first R.A.F. officer on the staff. His main job was to organise a school for radar training. It was estimated by the Signals Directorate that twelve N.C.O.s, twelve wireless operator-mechanics and twenty-four wireless operators would be required for four stations, Canew-don and Great Bromley, Essex, and Dunkirk and Dover, Kent. The men were posted to Bawdsey and in February 1937 the first radar-training school in the world was officially opened. Hart was to become one of the leading figures in radar operation and a major contributor to the evolution of techniques used in the Battle of Britain.
Watson-Watt suggested that women should be trained as radar operators as three typists at Bawdsey had adapted themselves excellently to the job. The Air Ministry at first objected that women might be emotionally unstable under the strain of operations. They relented, however, and women later proved their fortitude and reliability in the hectic summer of 1940 and throughout the war.
When the original recommendation was made in September 1935 for the erection of a chain of twenty stations covering the area from the Tyne to Southampton the R.A.F. requested a trial stretch over Southwold, Suffolk, to South Foreland by November with three operational stations by June 1936 and seven by August 1936. To ease the load, the requirement was reduced to the four stations mentioned above and Bawdsey.
Much had to be done in a very short time. Inevitably delays occurred while numerous problems were solved and modifications made. The attitude of some officials in Government departments who were quite unused to any sense of urgency, after eighteen years of peacetime plodding, did not help at all. In June Watson-Watt complained to Churchill over a cup of tea at Westminster of the frustration and time wasted by the machinery of officialdom.
Although it was proposed to complete the five ‘R.D.F.I’ stations of the first programme in time for the annual air-defence exercise, the delays meant that Bawdsey only was operational and had to bear the full brunt of the critical tests.
The results on the first day of the exercise, September 24th, were incomplete, irregular and inaccurate, but after recalibration of the station there was a marked improvement. Ninety reports were given in ninety minutes and on the following day 124 reports came in 115 minutes. With only one station for analysis, and this very much a research prototype, radar was unlikely to alter greatly the familiar pattern of the 1936 exercise: nevertheless Marshal of the R.A.F. Sir Edward Ellington, Chief of the Air Staff, visited Bawdsey in October and pronounced that despite everything radar should go ahead.
The first radar station in the world to form one of a chain was built entirely at the Bawdsey Research Station and handed over to the R.A.F. in May 1937. Dover Chain Home or ‘C.H.’ followed in July, and Canewdon in August.
It was estimated that a twenty-station chain would take two years to erect, but that with improvements to equipment fifteen stations could do the work of twenty. The remaining five stations could thus incorporate the cumulative results of research.
The whole of air defence was meanwhile being replanned round radar and the evolution of Fighter Command was entirely dependent on its success.
The problems of operating radar were by now multiplying at high rate, and presentation and transmission of information were among the most important. In 1936 Mr. E. J, C. Dixon, who was lent by the G.P.O., formed a separate laboratory at Bawdsey with a working copy of a group operations room. He was assisted by Warrant Officer R. M. Woodley, of the R.A.F.
Squadron Leader Hart, in addition to running the training school, started to develop the all-important ‘Filter Centre’ where radar information could be checked and analysed before being committed to a plot. An experimental filter room was opened at Bawdsey in July 1937 and passed information collected from the three radar stations to Fighter Command.
To sort out communication Mr. G. A. Roberts of Bawdsey was attached to the G.P.O. research station at Dollis Hill, London, while No. 10 department of the Royal Aircraft Establishment under Squadron Leader Rose co-ordinated ground and building design.
The three stations at Bawdsey, Dover and Canewdon were operating for the August 1937 air exercise. Despite errors which caused apparent failures, the results were promising, with ranges of 100 miles and formations of six or more aircraft observed at 10,000 feet and above.
Immediately after the exercise the Air Ministry drew up specifications for the twenty-station chain, and the scheme was approved by the Treasury on August 12th.
Already in January 1937 it had become apparent that industry’s help would have to be invoked to provide essential valves, transmitters and receivers. Metropolitan Vickers Ltd., of Manchester, heard that Watson-Watt was looking for special valves for new radio work. After detailed discussion the company’s research department was asked to undertake the development and manufacture not only of the valves but of the complete R.D.F.1 transmitter equipment.
In June 1937 verbal instructions were given to design and produce one set of ‘R.D.F. Transmitting Equipment’—a requirement increased in August to twenty-two sets when the Treasury sanctioned expenditure on the chain. A similar contract was awarded to A. C. Cossor Ltd., of Highbury, for receiving sets.
Complete secrecy was required in the two firms and separate buildings were provided for radar work. Only two men, Dr. J. M. Dodds of Metropolitan Vickers, and Mr. L. A. H. Bedford of Cossor, were initiated into the radar secret although others of the team came to know most of it by degrees. To assist security still further one portion of the transmitter, a small box, was designed separately from the rest so that it could be made by a specially hand-picked team. Because of the loyalty of the men in both firms no word leaked out in the ensuing years.
At Cossor’s a specially chosen team led by Mr. Puckle set about producing the first receiver in a private house in Highbury Grove, North London. The completed assembly assumed large proportions and holes had to be cut through the house walls for its removal.
Thus with complete co-operation between Bawdsey and the two companies radar passed from the laboratory stage to production.
The massive 350 ft. high transmitter masts of a typical Chain Home (CH) radar station in 1940