The RAF Fighter Control System
To control the fighters, Britain had a carefully set-up defence system which brought all the weapons available into play. It worked like this:
The sectors of 11 Group from an original map. HQ Fighter Command (RAF Stanmore) and HQ 11 Group (RAF Uxbridge) are marked in red, the sector stations are marked in blue.
First level control
Each Group was split into Sectors with RAF stations in each, one of which was the Sector Control Station. All the Sector Control Stations reported to the Group Headquarters, and they in turn reported to Fighter Command Headquarters at Stanmore in Middlesex, near London. The Headquarters acted as a filter and communications center.
The Sector Control Rooms at the Sector Stations reported to Group Headquarters, who in turn reported to Fighter Command Headquarters. This report would initially include Fighter Squadron status. For a larger view, click on any of the diagrams.
All round the coast were radar (Radio Detection and Ranging) stations, which could 'see' an enemy raid, in some cases while it was still over France. The raid was reported to Fighter Command HQ (FCHQ) where it was plotted on a large map. This information was then passed to the Group Headquarters, who passed it on to the Sector Control Rooms affected by the plot.
The RDF Chain reported to the Filter Room at Fighter Command Headquarters, this information was filtered then passed to Group then Sector level.
The RDF information was crude by modern standards, but was more than sufficient to give bearing and range information on an incoming raid. The system consisted of two dials and a cathode ray tube that gave a screen presentation of the raids range. The two dials supplied time and bearing information. The height of the raid could only be accurately provided once the raid came within visual sighting range of the Observer Corps posts. With experience, RDF Operators could judge the size of the raid by the size and shape of the blip on the screen.
The RDF screen. The readout at the top shows the ground return blip, from trees, buildings and any terrain near the station, at zero miles. The blip at 40 miles is the raid. The left hand dial shows a bearing to the raid of 89 degrees. The time on the right hand dial reads 11 hours, 10 minutes and 27 seconds from the inner dial outwards.
Observer Corps Reporting
All over the country were Observer Corps Posts. Their job was to report the raids once they had crossed the coast and were behind the radar. They reported to Observer Corps Centres, who passed the information on to their Sector Control Rooms, thence to Group Headquarters, who in turn sent it to FCHQ and the plot of the raid was kept up to date.
The Observer Corps Posts reported to their respective Observer Corps Centers, which reported in turn to their local Sector Control Rooms. This information then went to Group and HQ level, for onward transmission to the other sectors.
Primary Defence Control
All this information was passed up or down to the Sector Control Rooms, which actually directly controlled the defences. The Sector Controller then knew exactly where the enemy were and alerted the balloon sites in possible target areas to put up a balloon barrage. The balloons forced the German pilots to fly their bombers higher, which made bomb-aiming more difficult.
The Sector Controller also warned the anti-aircraft gun sites along the route of the raid, so they were ready to fire when the enemy came within range. Most importantly, he could scramble fighters from his Sector airfields and vector (direct) them towards the incoming raid. Without this vital system, time and fuel would have been wasted in constant airborne patrolling of the coast; some raids would have got through to their targets with no warning at all.
The Sector Control Rooms then alerted the Ballon Barrages and Anti-Aircraft guns, as well as controlling the Fighter Squadrons and giving them radio information about the incoming raids.
Controlling the Fighters
In order to vector the defending fighters on to an incoming raid, the controller had to know exactly where they were. The last link in the defence system, keeping track of the RAF fighters, were Direction-Finding or D/F radio stations. These also reported to their local Sector Control Room, and so up the chain of command in the same way as the Observer Corps. Again, this information was transmitted to every sector to keep the "Big Picture" spread throughout the command system. By doing this, the loss of a single Sector Control Room did not destroy Fighter Command's ability to function as an effective defence.
The Direction Finding stations provided the last link by tracking freindly fighters and reporting to the entire chain.
This control system is the source of many of the terms still used in air traffic control today. To assist the RDF and D/F operators, British fighters were equipped with a simple form of transponder, which automatically replied to interrogation from the ground systems with an identification signal. Known as IFF, or Identification Freind or Foe, it identified freindly aircraft on the screens. A secret device, it was code-named 'Parrot'. The instruction to switch it on was therefore "Squawk your Parrot". That term is still in use today as modern transponder codes are known as 'Squawks'. Steer is also still in use, and these remnants are a testimony to the basic soundness of the system of 1940.