Free The Battle of Britain by Bickers Richard Townshend Page A

the plots to a maximum of six Fighter Sectors. An Observer Corps Liaison Officer was on duty at each Fighter Group. At the period with which we are concerned, there were some 30,000 observers, manning more than 1,000 posts radiating from 32 centres.
    It was in the Sector Operations Rooms, ‘the sharp end’, that direct action against the enemy resulted from this nationwide and complicated network of interlocking data, which converged on the general situation map, the GSM.
    An Ops Room had a thick concrete roof and surrounding blast walls. The main floor was some five feet (1.5m) below ground level. The GSM, with plotters wearing head-and-breast sets sitting or standing around it receiving filtered plots, occupied most of the space. With a long rod like a croupier’s rake, the plotters moved arrows representing a single aircraft or a formation. A wall clock was divided into five-minute segments successively coloured red, yellow and blue. The arrows forming a track corresponded in colour with the current segment. Thus the Controller could see whether it was fresh or stale. Beside the track was a small block with an identification letter and track number. ‘F’ in red on a white ground stood for ‘friendly’. ‘X’ in black on a yellow ground meant ‘unidentified’. A black ‘H’ on yellow was ‘hostile’. A plot was known as a ‘raid’, whether identified as friendly or hostile.
    On the first tier of positions overlooking the GSM, running along one side of the large room, sat two NCO deputy controllers. On the next level, stepped slightly back, sat the Controller, a squadron leader in rank: in the early days of the war, this would be a pilot or observer, probably one who had flown in World War I. Gradually, to meet the growing need, non-flying officers were trained in the work. The Controller had two assistants: Ops B, a junior RAF or WAAF officer, and Ops A, usually an airwoman.
    There was also a Royal Artillery anti-aircraft liaison officer, who warned anti-aircraft sites when friendly aircraft were near their area and ordered them to cease fire when any entered it and also tried to prevent friendly aircraft being illuminated to the benefit of the enemy.
    On the wall facing the Controller’s dais were the clock, and the aircraft state boards on which the number of aircraft available in each squadron was shown, with the various states of availability to which the Group Controller had ordered them.
    â€˜Stand-by’ meant that the engine had been warmed up and the pilot was strapped into his cockpit, ready to be airborne in two minutes. ‘Readiness’ called for pilots to run to their aircraft and take off within five minutes. The average time for a whole squadron to be off the ground was three minutes. The usual states of availability were 30 minutes or an hour, which meant that pilots had to be at their dispersal point on the airfield perimeter, either in the rest hut or, in fine weather, sitting outside it. Sometimes the Group Controller would order 10 or 15 minutes availability, or two hours, when pilots were allowed to be anywhere on the station (in their messes, if they wished). The final state was ‘Released’.
    Ops A took instructions from Group – such as ‘One flight of 222 Squadron come to readiness’; ‘64 Squadron to 30 minutes’; ‘56 Squadron released’. He wrote this on a pink form and gave it to the Controller who, having read it, handed it to Ops B, who took action. For example, this might have involved calling the squadron concerned on the telephone and passing on the order.
    Behind the Controller’s dais were four radio-telephony (R/T) cabins with WAAF, or airmen on listening watch. The transmitter was situated elsewhere within the station, on open ground. The HF receiver was in the cabin and the operator had the often difficult job of tuning it. When, late in the Battle, VHF began to be