SOME HISTORICAL NOTES
The development of radio was the result of studies carried out by many eminent scientists during the early part of the 19th century. Probably one of the most significant was James Maxwell (1821-1879) a British Physicist who developed the theory of electro-magnetism and predicted the existence of electromagnetic radiation. Herman Helmholtz (1821-1894) carried out research into oscillating electric currents. Further important contributions were made by Oliver Heaviside (1850-1925) and Arthur Edwin Kennelly (1861-1939) who predicted, almost simultaneously, the existence of a layer of ionised gas, some 90-150 km. above the ground. It would have the ability to reflect medium frequency radio waves and because of this reflection radio waves can be propagated beyond the horizon. This is important because it enables long distance communications to take place. Guglielmo Marconi first demonstrated this facility in his famous transmission in 1901 (using a spark transmitter) from Poldu in Cornwall to Newfoundland in Canada.
This success was followed by the development of more powerful radio transmitters and more sensitive receivers. The ability to include sound in the transmitted signal soon followed. This resulted in the fitting of radio equipment on board ships enabling ship-to-ship and ship-to-shore communications to take place. The value of this new facility was soon demonstrated when the Titanic on her maiden voyage struck an iceberg in mid-Atlantic and sank. The ship’s radio operator sent out a distress signal, which was received by the RMS Carpathia, causing her to rapidly steam to the Titanics’ last known position, managing to pick up some survivors.
Attention then turned to the design and construction of radio stations to broadcast news and entertainment to the general public. The Marconi Wireless Telegraph Company was established in the early 1920s and built a radio production factory in the centre of Chelmsford Essex. In the grounds of this factory two 450 ft. high steel towers were erected separated by some 600 feet. A double wire aerial was slung between the tops of the towers. This aerial system together with a transmitter operating at 1500 metres wavelength was given the code name 2LO and was the first radio broadcasting station for the newly formed BBC. This was followed by the construction of a medium wave transmitter at Daventry in 1925.
The introduction of radio was important in the context of radar and indeed other electronic systems such as navigational aids. Factories were built to meet the demands of this new business, thus providing the manufacturing resource to meet the needs of the war effort. Additionally, universities and technical colleges introduced courses to teach young students in the new electronic disciplines, providing a pool of trained people for research and engineers for the Armed Forces.
Christian Hulsmeyer (1881-1957) of Germany is credited with the first practical demonstration of an equipment to detect ships at sea. In 1904 his ‘Tele-Mobilescope’ was shown in Cologne and proved that radio detection of targets was possible. The detection ranges were very short, presumably due to low receiver sensitivity or low transmitter power or a combination of both. Although the product was patented in 1904 in both Germany and Great Britain, it was seen not to be commercially viable. David Pritchard’s book ‘THE RADAR WAR’ gives a good description of Hullsmeyer`s work together with a copy of the original block diagram. It was not until the 1930s that any significant further advances were made.
Many books have been written about the early days of radar and the numerous applications, which followed. Two books are worthy of special mention. Jack Gough`s book, entitled ‘WATCHING THE SKIES’, details the years immediately after the Second World War and discusses the UK`s Ground Radar System from an M.O.D perspective. It is a comprehensive account of the political background lying behind the decisions, which resulted in the establishment of the post-war radar defence network known as ROTOR. Some information on this is contained in Appendix 2 of this book.
The book ‘RADAR DAYS’ by Dr. E.G.Bowen recounts the contribution made by Sir Henry Tizard, Watson-Watt and A.F.Wilkins to the development of radar in the years just prior to WW2.
Jack Gough`s book although excellent in content, is somewhat ‘heavy going’ as a read. E.G.Bowen`s book, on the other hand, although very informative, is in a lighter vein and because it contains many kindly anecdotes relating to colleagues and others it is a very interesting and entertaining book to read.
During the late 1930s it became apparent that Germany was on course to launch a war of conquest in Europe. The bombing of Guernica by German aircraft on April 26th during the Spanish Civil War caused much destruction and loss of civilian lives. To counter this type of threat, Britain did some preliminary studies on the possibility of destroying enemy aircraft by the use of a ‘death ray’ generated by a powerful focussed radio beam directed at the enemy aircraft.
Arnold F. Wilkins, an engineer working for Robert Alexander Watson-Watt, at that time Superintendent of the Radio Research Station, part of the National Physical Laboratory at Datchet in Berkshire, did some calculations, which showed that the power required in the radio beam to destroy an aircraft was not a practical proposition.
An earlier report by the British Post Office Engineering Department had reported that an aircraft flying through an experimental radio beam had caused the beam to ‘flutter’. Wilkins had read this report and thought that it indicated that the aircraft had re-radiated some of the energy in the radio beam. He did further calculations, which convinced him that it would be possible to design equipment that could detect and track an aircraft.
Robert Watson-Watt wrote a memorandum describing the results of Wilkins work and claimed that equipment could be designed, which would have a high probability of successfully performing detection and tracking of aircraft.
At a meeting on Wednesday 13th February 1935, Air Vice-Marshall Dowding agreed to a series of tests to check whether the claims made by Wilkins and Watson-Watt could be substantiated. For the period of the tests the RAF loaned a Handley-Page Heyford bomber to act as the ‘target’ to be tracked.
The tests were to be carried out near the little town of Weedon near Daventry. The pilot of the Heyford was instructed to fly on a path between Weedon and the BBC transmitter at Daventry. The detection equipment was mounted in a small van underneath the flight path and was tuned to the 49-metre wavelength of the BBC transmitter. The rectified received signal was displayed on an oscilloscope.
The pilot of the Heyford took off from Farnborough early on the morning of the day scheduled for the test and started to fly the course laid out in the flight plan. As the Heyford flew over the van housing the radio detector, the previous steady signal of the Daventry transmitter began to vary in amplitude indicating that a measurable amount of radio energy was being reflected from the aircraft above.
The Air Ministry men in the van watched and as the reflected signal from the aircraft indicated that the aircraft was in their vicinity, they were able to track it for five minutes, corresponding to a distance of approximately eight miles. The experiment had been a complete success and had proved conclusively that the detection of aircraft by radio means was possible.
Following the success of the February 1935 test, Watson-Watt’s team was moved to the remote site of Orfordness on the Suffolk coastline, 90 miles Northeast of London. Here they began the erection of the very first experimental radar system. In mid June 1935, they had succeeded in detecting radar echoes from a flying boat at a range of 17 miles, and by September the range for the detection of aircraft had increased to 40 miles. By the end of 1935, detection range had increased to 80 miles.
In March 1936, the Orfordness group was moved to Bawdsey Manor, a little further down the Suffolk coast. By this time work had started on the construction of a large chain of radar stations around the coastlines of England and Scotland that became known as ‘CHAIN HOME’. This, together with a later radar system called ‘CHAIN HOME LOW’, formed the radar detection and tracking facility, which played a vital part in the Battle of Britain.
It is to be noted that the presence of the ‘Heaviside’ layer also enabled radar engineers to design long range radars - termed ‘Over The Horizon Radars’ to detect and track missiles. These radar stations were established in a number of countries (USA, France, Australia etc) during the Cold War period. Most, if not all, have now been dismantled. The only known British site was at Thorpness in Suffolk.
There are many scientists and engineers who contributed to the development and application of radar. The following is a very brief listing of those who made an outstanding impact on this new technology.
Sir Robert Alexander Watson-Watt. LLD, DSC, Order of the Bath, FRS. was born in 1892 and died in1973. He is generally acknowledged to be the father of British radar. He was educated at the University of St. Andrews in Scotland. After graduating in 1912 he immediately joined the faculty but found his academic career disrupted by World War 1. He spent much of the war working as a meteorologist at RAE Farnborough attempting to locate thunderstorms with radio waves. He remained in the scientific civil service after the war and in 1921 was appointed superintendent of the Radio Research Station at Slough.
The development of radar was very much a team effort with Watson-Watt as the captain. Throughout the war he was increasingly concerned with coordinating the expanding effort in the radar field. He visited the USA in 1941 as an advisor to the US Government. In 1946 he left government service to become a consultant. He was elected a Fellow of the Royal Society in 1941 and was knighted in 1942. (One of Watson-Watt`s forebears was James Watt who developed the steam engine, the main source of power to drive machinery during the industrial revolution).
Sir Henry Tizard (1886-1959) served in the Royal Air Force from 1918 to 1919. In 1933 after a distinguished career in Chemistry he was appointed as Chairman of the Aeronautical Research Committee and served in this post for most of the Second World War. He supervised and championed the development of radar in the run-up to the war. After the war Tizard served as the Chairman of the Defence Research Policy Committee and president of the British Association.
Sir Henry’s scientific philosophy can best be summed up by a remark he once made “The secret of science is to ask the right question, and it is the choice of the problem more than anything else that marks the man of genius in the scientific world”
John Randall and Harry Boot working at Birmingham University in 1940 invented the resonant cavity magnetron and produced and tested a prototype. All cavity magnetrons consist of a hot cathode with a high (continuous or pulsed) negative potential from a high-voltage direct current power supply. The cathode, which emits electrons, is built into the centre of an evacuated, lobed, circular chamber. A magnetic field parallel to the length of the cathode is imposed by a permanent magnet. The magnetic field causes the electrons, attracted to the (relatively) positive outer part of the chamber, to spiral outward in a circular path rather than moving directly to the anode. Spaced around the rim of the chamber are cylindrical cavities. The cavities are open along their length. As electrons sweep past these openings, they induce a resonant high frequency radio field in the cavity, which in turn causes the electrons to bunch into groups. A portion of this field is extracted with a short antenna that is connected to a waveguide, which in turn directs the extracted radio frequency (RF) energy to the antenna system of ‘THE RADAR’.
The magnetron is a self-oscillating device requiring no active external elements other than a power supply. In pulsed applications (as generally used in radar) there is a delay of several cycles before the oscillator achieves full peak power and the build-up of anode voltage must be coordinated with the build-up of oscillator output. The magnetron is a fairly efficient device. Large peak power outputs can be achieved. The Type 80 Mk1 S-band Defence Radar, described in this book, had a peak power of 1.0 Mega-watt. The later version, the Mk3, radiated a peak power of 2.5 Mega-watts.
Dr.E.G.Bowen. When the losses sustained by the Germans during the daylight raids during the Battle of Britain became unacceptably high, they turned to night-time raids. This reduced the ability of the RAF fighters to shoot down enemy bombers. Watson-Watt set Dr. Bowen the task of developing an-airborne radar which when fitted into the nose of a fighter aircraft could search out and lead to the destruction of the potential enemy bombers. This task became possible after the magnetron came into service, its compactness and low input power requirements could for the first time enable centimetric radar to be fitted in fighter aircraft.
The new radar, given the code-name H2S, became very effective, and the RAF ‘kill-rate’ rapidly rose. As a result, the UK government ‘leaked’ to the media that the RAF had selected pilots who had remarkable ‘night vision’ abilities in the hope that the Germans and the British people would be hoodwinked into thinking this was the reason for the high success rate. One particular pilot named Cunningham became known as ‘Cats eyes Cunningham’ and was regarded as a national hero.
The H2S radar also provided valuable assistance to Bomber Command. As well as providing fighter aircraft with an interception facility, H2S fitted to Pathfinder Squadrons, provided the pilot with a radar plot of the terrain below thus enabling the dropping of target markers on selected targets guiding the main bomber force to locate and bomb the right target.
A bonus was provided by H2S in the form of storm warning. The forward looking radar beam showed on the radar screen the returns from ice and rain ahead, providing the pilot with the means of avoiding dangerous weather situations.
In the spring of 1940, Britain was virtually without allies. Germany was well on the way to occupying a large part of Europe and Sir Henry Tizard realised that it would not be long before the British productive capability would not match that of Germany and the countries then in her occupation. He recognised that if America did not enter the war, Britain could not win without the research and productive capability of the North American continent. This was particularly true in the field of electronics, which was already playing a crucial part in the conduct of the war.
He therefore made the bold suggestion that Britain should handover her wartime secrets to the USA in exchange for research and productive capacity. Agreement was reached with the USA in July and the members of the team were chosen in August arriving in Washington early September 1940. The team was made up of 3 senior scientific service personnel Tizard, Professor John Cockcroft and Dr.E.G. Bowen.
The purpose of the mission was to hand over to the US Services all the recent British technical advances. These included virtually every British secret, the jet engine, rockets, radar etc. Nothing was excluded.
What has to be further recorded is that bringing basic radar techniques to the benefit of the greatest possible number of ‘end users’, in reliable product form, took and still takes scientists, engineers and technicians of the highest calibre, who press the boundaries of the best knowledge of their time, taking ‘Research’ into the realms of ‘Development’ and then to Manufacture.
While impressed by the early discoveries at Orfordness we who gather at THE RADAR COMPANY reunions at Cowes are impressed by what has been achieved in enhanced radar performance during recent past decades, and submit that today’s achievers can also anticipate being impressed by those that will follow them.
‘Our’ book, ‘THE DECCA LEGACY’, opens at the time of the thermionic valve, the slide-rule and the wartime spirit that permeated product and project design teams, transcending financial reward while focusing on the scientific advancement, and more importantly the aid extended to the end user.
It tells of how radar products were designed to meet the needs of maritime enterprise, those of air and sea travel and transport industries, also as sensors for those engaged in meteorology as well as tools for each of our armed services.************************************************************************
On one occasion, later in life; a radar-gun toting policeman, reportedly, pulled over Watson-Watt, in Canada, for speeding. His remark was “Had I known what you were going to do with it I would never have invented it,” He wrote an ironic poem afterwards entitled ‘Rough Justice’
"Pity Sir Robert Watson-Watt, Strange target of this radar plot And thus, with others I can mention, The victim of his own invention, His magical all-seeing eye, Enabled cloud-bound planes to fly But now by some ironic twist It spots the speeding motorist And bites, no doubt with legal wit The hand that once created it".