The Wartime Memories Project - RAF Filter Rooms

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The Filter Room was the nerve centre of the Radar system. Information was sent from the many Radar stations which formed a chain of protection around our coasts, this information was then "filtered" by the young women of the WAAF and represented on the map table by markers which were moved as the information was updated. From this display the Officers controlled the battle.

There were 7 Filter Rooms in Britain, each controlling its own area. These were manned 24 hours a day through out the entire war.

  • RAF Barnton Hall 9 Group Fighter Command
  • RAF Bentley Priory. HQ Fighter Command
  • RAF Kenton Bar & Blakelaw. 13 Group Fighter Command
  • RAF Raigmore. 13 Group. Fighter Command
  • RAF Watnall. 12 Group Fighter Command


The Filter Room

"Must be under twenty-one years of age, with quick reactions, good at figures - and female". These were the prerequisites for members of the WAAF seeking a commission as Officers working in the Filter Room. This secret section of the RAF's Defence programme in World War Two has never had the recognition it deserves. Nevertheless, it was one of the greatest aids to protection of Britain and to our air operations of the whole war.

The reason that very few people even today have heard about this is the extreme secrecy which the personnel maintained about its work and its influences. Only in recent years have the restrictions been lifted and wartime members of this close group been freed from the silence imposed upon them.

The work done by the airwomen plotters of the Filter Room, the Movement Liaison Officers and the Filterer Officers who were responsible for calculating and rectifying the position, and identifying the hundreds of tracks of hostile and friendly aircraft leaving and approaching the coasts of the British Isles, was vital.

It is time that their valuable contribution to the Battle in the air be recognised. The Filter Room was the nerve centre of the Radar system. It received information from the many Radar stations which formed a chain of protection around our coasts. This information, due to the early primitive forms of detection equipment and the possible human error of its operators needed to be instantly corrected, co-ordinated and displayed on a huge map table of the area concerned, in a form suitable to be passed on to the Operations Rooms. Without this essential link, the Radar information at that time could not have been used.

This cleaned-up (or filtered) information we have all seen in many films where WAAF Ops room plotters move coloured arrows around a map table, using a long pole-like contraption. It always appears so peaceful and bears no relation to the hectic activity occurring in the Filter Room.

From this information, orders were given by the Senior Officers observing from the gallery above the Ops table, for air raid warnings to be sounded in threatened areas, fighter squadrons to be scrambled, incoming hostile aircraft be intercepted and returning bomber aircraft in difficulties monitored so air-sea rescue boats could be directed to their assistance, should they ditch. The ack ack gun sites and balloon barrage stations also relied on this information.

The country was divided into seven regions, including Northern Ireland and the Scottish Islands and there was a Filter Room for each. These were manned for twenty-four hours daily from the commencement of hostilities until after peace was declared in Europe. Personnel were formed into four watches. Sometimes it was impossible through illness or shortage of trained personnel to maintain this and a three-watch basis was instituted. This meant leave was impossible and other than eating, sleeping and working, there was little time left.

Personnel had two fifteen minute periods when possible during the watch for a refreshment break. The food available varied considerably. Sandwiches of marmite and raw cabbage were offered throughout the night watch for weeks on end at one particular station! Working conditions were often difficult and unpleasant. Many of the centres were underground where ventilation and heating left much to be desired.

The pressure of work depended upon the amount of aircraft activity and also the region involved. Naturally the northern areas were not as busy as the Filter Rooms covering the coast from the Wash to the Isle of Wight, (11 Group), and the Isle of Wight to Wales (10 Group). The weather too was a key factor in the activity to be expected so meteorological advices were posted constantly.

The requirement for the Filterer Officers to have quick reactions was patently obvious. They had to sort out the correct position of the aircraft from the various overlapping Radar station plots which covered the same aircraft responses. They needed to estimate both height and number of aircraft, as well as direction from information given, having intimate knowledge of the siting of the Radar stations involved and judging their accuracy. All of this had to be done with great the aircraft themselves were constantly moving on to new positions. It was found that male Filterers, mostly well over thirty years of age were far too slow during periods of intense activity and they had to be removed from the table!

For the displayed information to be of value to the Operations Room, it had to be as up-to-date as possible. This meant that in times of the greatest activity, a Filterer Officer must estimate and display salient information on up to fifty different tracks within a minute. The mental stress and physical strain were intense under these conditions and when the personnel came off watch, whether officer or airwoman, tension was invariably high. Throughout the meal supplied when coming off duty, the atmosphere was almost hysterical as they gradually unwound. Quite often however tired, sleep was impossible.

On the whole, it was amazing how few buckled under the strain. They all realised the importance of their work and it took a really major illness to prevent them from appearing for duty. However, subsequently, time has taken its toll of some amongst that small group. There have been instances of suicide, of recourse to alcohol in later years and bouts of deep depression. This is not to be wondered at when one considers that whilst filtering the tracks of the bomber squadrons on operations over Germany or plotting fighter sorties against incoming hostiles, these young women knew that their own husbands or sweethearts were amongst the aircrews. They would count with trepidation the numbers of the returning Allied aircraft.

The mixture of backgrounds amongst the members of the Filter Room officers was amazing. Most of the senior male officers hailed from the Stock Market where they worked as jobbers and brokers. It was an inspiration on the part of the RAF to choose these men for the positions as Controllers and Movement Liaison Officers. All personnel involved had to have quick reactions, good mathematical ability and be physically very energetic. The women chosen ranged from psychology or science students, young actresses, county debutantes, grammar school high flyers to daughters of famous people - novelists, painters, musicians and vicars. But they were all dedicated to their work.

Many friendships were forged under these conditions and remain close until today. Now the strictures of secrecy have been lifted, it is surely right that their dedication should be recorded. The importance of their work in the defence of Britain together with their contribution to the successful invasion of Europe and the ultimate overthrow of Hitler's forces should be made known.

Eileen Younghusband

Read more of Eileen's experiences.


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