In fact, progress was faster than any had hoped: a team assembled in May 1935 had 70-foot-high masts erected, and tests started within the following month. By the end of the year, results were far beyond anything Watson-Watt had promised. He had interpreted the fluctuations of a signal to guess that a formation of three Hawker Hart had strayed across the test area. He had measured aircraft heights to within 1,000 feet and had got some way to solving the direction-finding problem. The team mounted directional aerials to face north, south, east, and west and then measured the relative strength of signal. The results were enough to distinguish the British work from anything done elsewhere, and more than enough to provide Watson Watt with government money for higher masts and to get research started on alternative wavelengths (in case of enemy jamming) and detection of low-flying aircraft. The money was approved by Dowding but the gruff old man never did endear himself to the scientists, and many of them thought wrongly that Dowding did not understand the scientific principles of the new device.
There was a unique atmosphere at Bawdsey, to which the researchers moved in 1936. The old manor house was by the sea. It had extensive grounds that included a cricket pitch, peach trees, and the biggest bougainvillaea in the country. The high-grade academic physicists lived and worked in the manor house. There was no red tape and they stopped work for a swim or a bit of gardening as they felt like it. On the other hand, it was not unusual for the laboratory to be in full operation long after midnight Visitors came from the famous Cavendish Laboratory at Cambridge to sit round the fire and talk shop. These sessions grew into what the Bawdsey men called 'soviets' in which visiting civil servants, Air Marshals and eventually air crew straight from operations could say anything they liked to anyone they chose. An Assistant was often actively abetted in arguing with an Air Marshal, said an unrepentant Watson-Watt, who was often fomenting such excitement.
It was in this atmosphere of middle-class comfort that senior officers met scientists, with no clearly defined division of authority. No visitor to Bawdsey could fail to see its value as a way of applying scientific method to war. From Bawdsey, in 1937, teams went to study the discrepancies between radar tracks and navigators' logs. Another team went to Fighter Command. The name 'Operational Research' was coined by Watson-Watt. He defined this as "investigation by scientific method on actual operations current, recent, or impending and explicitly directed to the better, more effective and more economical conduct of similar operations in the future." Although it never got the public attention that radar attracted, Operational Research eventually became just as important to the progress of the war.
IFF
By 1938 many airmen were worried that the radar could not identify friendly aircraft. It was typical of the negative attitude of most brass hats when the Commander in Chief Bomber Command said he would do everything in his power to oppose the radar work unless this problem was solved. Eventually it was solved, up to a point. It was called Identification Friend or Foe — IFF — a device for every aircraft. This re-radiated a much more powerful pulse than the one it received (but on the same frequency) so that its blip on the radar screen could be identified as that of a friendly aircraft.
The Reporting Network
The sort of radar defence that Britain had built by 1939 could only have grown out of the informal interaction of scientist, airman, and civil servant. Part of Watson-Watt's genius was knowing what was possible, so that as the government put money into research they found his promises fulfilled. But the great achievement of British radar was not to be found in the rather crude Chain Home RDF stations or the more sophisticated CHL (Chain Home Low) sets but in the way its information was interpreted and used. In this respect it was most fortunate that Dowding, who gave the first go-ahead for radar, then became Chief of RAF Fighter Command.
Bawdsey became the first radar station, as well as the scientific laboratory. Here, too, there were RAF officers planning the training of the personnel needed to man the other stations. Additionally they set up a full-scale experimental Group Operations Room, and experts were already planning the immense network of telephone cables that would be needed to feed all the information back to other such control centres.
By January 1938, Fighter Command aircraft at Biggin Hill airfield were working under radar control from the station at Bawdsey. >From this time onwards, civil airliners passing within range of the Bawdsey apparatus had fighters sent to intercept them for practice. When war began, the operators were able to track German bombers mine-laying in the Thames Estuary. Sometimes the radar was so accurate that RN minesweepers could find the mines immediately.
The canny Scotsman Watson-Watt had proved to be the perfect man for the job, in spite of many bitter disputes in which he was involved. His knowledge of pure science gave him the basis upon which to work and his experience with electrical storms stood him in good stead at a time when electrical disturbance was one of the worst problems of practical radar. His career as a scientist for government departments equipped him for the internal politics he now encountered, and above all he was driven by a sense of urgency that made him set time limits to research, after which equipment went into production whatever its state of development.
The scientists realized that the quality of radar would depend upon generating very high power for very short wavelengths. Already the original experiment's 50-metre wavelength had been reduced to 10 metres for the chain of stations that was being erected round the British coast. For a supplementary chain (CHL) the wavelength was only 1.5 metres. The shorter wavelengths provided a narrow beam that was far more directional. So the CHL masts had rotating aerials that swept the horizon to find the maximum intensity of response. These CHL sets were largely due to the work of an Australian named W. A. S. Butement, a War Office scientist who had started such beamed radar experiments as early as 1931 but had been discouraged from continuing with them.
But, even by 1940, it was still very difficult to read the blips on the cathode-ray tubes and height estimation was done by comparing the signals of different aerials. Judging the number of aircraft in any formation just from the wobble of the cathode's glow was even more illusive. And when the operators were reading many blips at once, and trying to distinguish single aircraft from large formations, the results were confused and contradictory.
The Filter Room
From each of the Chain Home stations they phoned the details seen on the cathode-ray screens to a Filter Room at Bentley Priory. (This room also received reports from the Chain Home Low stations that searched for low-flying raids.) The Filter Room exemplified the way in which the whole radar system reconciled man with machine. Here the reports from the radar stations were weighed against the accuracy of their previous reports and against known faults in the apparatus. Only after the reports were compared, judged, and interpreted were they passed on to the Operations Rooms. A good example of the value of the Filter Room was 'range-cutting'. The Chain Home stations were far more accurate at measuring range than finding direction, so the range reports from two neighbouring stations could be intersected to provide an accurate position.
Another important task was comparing the reports of enemy raids with the estimated position of any RAF aircraft that might be seaward of the radar chain. The IFF system that enabled friendly aircraft to characterize the blip they made on the screen was far from perfect. It remained the weakest link in the system for a long time and eventually was radically changed. Meanwhile the Filter Room was responsible for preventing RAF squadrons from attacking friendly aircraft.