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Chapter 2 - The Need

The successful experiments in Radio Direction Finding (RDF) conducted in the summer of 1936 formed the embryo of a technique which revolutionised the fighter defences of the United Kingdom, and which proved invaluable during World War II.

The first experiments in directly controlling fighters took place at Biggin Hill in Aug 1936 and were conducted by Henry Tizzard. The bombers were allowed to change direction at random creating numerous re-calculations and subsequent failure of the intercept. Later, a second, seasoned ex-pilot sector commander took a hand and during the sortie, having judged the angle with his eye, quickly said, "Tell him to fly 070 degrees", which concluded in a successful intercept, showing that promptness was possibly more important in control than accuracy.

The initials "RDF" were accepted as being a suitably vague, but not an unconnected term, for Watson Watt’s invention and were a little less dramatic than the public’s perception as a "death ray". The term RADAR did not come into general use until 1941 when it was coined in America as an abbreviation for RAdio Detection And Ranging.

It soon became apparent to Hart that the passing of information on detected aircraft could become confusing and dangerous, particularly when two or more stations were reporting on the same aircraft or group of aircraft. Hart introduced the concept of a "filter room", a sort of half-way clearing house between the RDF equipped stations and the Operations Centre. During the Home Defence Exercise of 1938 RDF messages were passed to a filter centre at Bawdsey, filtered and then passed to Fighter Cd HQ 11 Gp, Uxbridge and Biggin Hill for use by experimental controllers. Post "Home Defence" the a/c reporting and fighter control system began to take definite shape. The reporting system, providing early warning and tracking of hostile a/c was controlled and manned by 60 (signals) Gp. The control system were maintained by 60 Gp personnel but was controlled and manned by Fighter command (fighter controllers were trained by user Gp HQs at this time).

The system required all plots from all the radar stations to be passed to, and displayed in, a Filter Room (16),where a filterer, the forerunner of today’s Track Production Officer, would correlate all the duplicated plots, assess the true situation and the "cleaned" picture would be voice told to the Operations Centre and displayed on the General Situation Map (GSM), this system was also known by wartime exponents as "mad Ludo". (17). The Interception Controller in the Operations Centre would calculate the intercept vector for the fighter aircraft under his control using the relative positions as shown on the GSM. Using R/T, the Interception Controller would then direct the fighters until they were visual with the target.

One source of constant concern was the time lag between the detection of an aircraft at the radar station and the appearance of a corresponding plot on the GSM. The increasing speeds of new types of aircraft made rapid plotting, filtering, identification and voice-telling all the more important. Height reports of aircraft received from two different stations sometimes conflicted widely and to use an average between two heights reported as 3000ft and 17000ft was clearly of no value to the interceptor, particularly when visibility was restricted by poor weather and with no on-board radar (a little like modern radar heights!). Obviously the most difficult factor was the ever present need for lightning decisions and the knowledge of the grave consequences of miscalculation. There were other problems which were summed up in a 1939 Air Ministry report:

"In the early days when radar was just beginning, the whole system from radar station to filter room was in the hands of enthusiasts, each selected for his particular suitability for the task. In the air exercises of 1938 it produced excellent results.........Since those days there has been a rapid expansion and consequent dilution of experience and technical aptitude, today the results are markedly inferior. Fighter Command has always had difficulty in finding filterers capable of replacing the original men (sic), and NCOs of all trades were misemployed as filterers in an endeavour to achieve efficiency. It became apparent that without adequate filtering, the Interception Controller lacks the correct information to achieve the maximum number of interceptions, and the fighter defence of the country could be severely handicapped. Therefore the 10.5 million pounds sunk into the radar organisation might never give the results it should be capable of".

These concerns were the Genesis for the SFC the first ever of its type in the world. Financial approval for the appointment of junior officers to fill filter posts in lieu of NCOs was given on 9 April 1940. It then became possible to select only those with the aptitude and qualifications for the task. Usually they were university graduates in scientific or mathematical subjects. Whilst it cannot be said that all filtering troubles ceased, there was undoubtedly an improvement in the quality of essential information presented to fighter operations and intercept controllers. The appointment of the first fifteen trained filter officers occurred with the opening of the Controller Training Unit (CTU) on 10 June 1940.

Having the need is of course only the first step, the type of personality who will be required to be trained to perform the task of controlling was thoroughly discussed at the advent of the School and continues as an absorbing topic today. A report compiled by Gp Capt Cherry before he retired at the end of W.W.II gives a comprehensive list of the ideal qualities in his (and my) opinion:

"Selection of Fighter Controllers - Generally

Before the war it was assumed that previous flying experience was essential in a controller. This was disproved and the following conclusions can now be stated as the result of practical knowledge gained during the last 6 years:

a. The ideal temperament for a controller should include the following characteristics:

i. a young, quick mind (men who started controlling when over the age of 40 years seldom made really good controllers). (Where have I heard that before!)

ii. initiative.

iii. ability to remain calm under stress.

iv. reliability

v. enthusiasm

vi. intelligence

vii. tact

viii ability and willingness to take responsibility

ix. ability to command respect

x. ability to understand and appreciate the point of view of the aircrew being controlled, their difficulties and the limitations and possibilities of the aircraft in which they are flying. (All Lightning controllers: give the time, distance covered and fuel used when a Lightning accelerates from .9 to 1.3? Ed)

Mind you the Gp Capt also advocated the training of some fighter pilots and other aircrew as fighter controllers, as follows ".......each pilot and navigator in a fighter squadron should take turns as controller under instruction at regular intervals." Another recommendation was for Control Liaison Officers to be appointed on each fighter squadron. Sounds like a job for the girls!

The year 1939 was, for obvious reasons, a time of great innovation. On 30 Jun that year IFF was first put into production. In Jul a signals school was proposed for RAF Yatesbury and in the following month the Air Ministry instructed that Leighton Buzzard Wireless Stn be opened for the training of WAAF plotters and General Duties No1s under the auspices of Fighter Command. Wg Cdr Hart was selected to instruct the initial trainees. At the beginning of Sep, two days before the declaration of war, a Signal Training School was formed at RAF Bawdsey to train RDF operators of Trade GpII. On 3 Sep 39, the day war broke out, the research establishment at RAF Bawdsey was disbanded and relocated to many different places because the location was considered to be high risk being on the south east coast of England. On 19 0ct 39 attempts to move RDF from Bawdsey to Yatesbury failed as Yatesbury was considered to be over-manned having a total of 5,729 personnel.

By Jan 1940 the R/T Speech Unit had been formed at Duxford to instruct on a type of speech, which proved by experiment and practice to give most satisfactory results. By mid 1940 Fighter Command HQ filter/ops room and the R/T Unit had moved to HQ11Gp Uxbridge, RDF courses had commenced at Bawdsey and airmen were being trained as plotter/filter room assistants at Leighton Buzzard.

Continue to the next part of the history ......