Blakelaw Filter Room
This facility was somewhat smaller than the Group Headquarters, but built to a similar pattern.
Filter rooms were the nerve centres of the UK radar system and vital to the success of Fighter and Bomber Command headquarters throughout the country. Information from Radar Stations, airfields, aircraft and ROC posts were directed into the Filter Room. From here, a dedicated and hard working team of RAF personnel collated all of the information to provide an as accurate as possible air picture to be passed onto the Operations Room where, commanders could direct aircraft resources.
The work done by the WAAF plotters of the Filter Room, the Movement Liaison Officers and the Filter 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. Working conditions were difficult; ventilation and heating were poor. 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 a popular snack!
The requirement for the Filter 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 siteing of the Radar stations involved and judging their accuracy. All of this had to be done with great speed as 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 Filter Officer must estimate and display accurate 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 airman, tension was invariably high. 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 vast. Most of the senior male officers hailed from the Stock Market where they worked as 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, and grammar school high flyers to daughters of famous people – novelists, painters, musicians and vicars. But they were all dedicated to their work.
At approximately the same time another underground bunker was constructed. The communications bunker. All communications from airfield squadrons, aircraft and group headquarters were relayed through here before branching off into either the Filter room or direct into the Operations bunker. (The location of the Communications bunker is not known)
Information from http://www.websitedcm.com/bunker/filterroom.htm