This New Year's Day marked an important anniversary for RAF Boulmer's Air Surveillance and Control System. Eighty years ago, the first radar unit dedicated to the control of aircraft from the radar itself became operational at RAF Sopley in Hampshire. This heralded the dawn of the era of 'radar control', which is the basis of RAF Air Operations Controllers' work today.
Throughout the Battle of Britain, Chain Home (CH) and Chain Home Low (CHL) radars had been used for early warning. With information presented to them on as counters on a 'Plotting Table', Sector Controllers could generally position their fighters within 5 miles of an enemy formation. At this range, pilots could usually gain visual contact with enemy aircraft and take over the interception.
However, in the autumn of 1940, the Luftwaffe switched to night bombing - the 'Blitz'. The CH and CHL radars still gave warning of bombing raids but Sector Controllers struggled to position friendly fighters close enough to see an enemy aircraft on all but the brightest moonlit nights - Fighter Command could not contest the night skies over the UK in same way it did in daylight.
Three advances combined to solve the night-time interception problem, and they all entered service around the turn of the year 1940-41. The first was the Bristol Beaufighter, a fast, powerful twin-engine fighter with two crew. It was fitted with the second advance - Air Intercept (AI) radar which, if the aircraft was positioned correctly, could guide it from its maximum range of several miles down to several hundred yards behind the enemy aircraft.
However, the third advance was the key without which the other two would not have worked - a specialist 'Ground Controlled Interception' (GCI) radar from which the Beaufighter could be placed in a position to use its own radar.
This GCI radar - initially the mobile Type 8, to be replaced by the static Type 7 - was an improved version of the existing CHL radar.
Modifications included an antenna providing accurate height information; a motorised turntable, which allowed the antenna to sweep through 360 degrees at a constant rate; and a 'Plan Position Indicator' (PPI), which enabled the radar to be displayed as we would recognise it today for the first time - the radar appeared at the centre of the screen with aircraft 'blip' displayed at the correct range and bearing from the radar, presenting a map-like overview of the air situation in real time. A controller sitting at the radar could thus see both their fighter and target at the same time, and manoeuvre the fighter into the correct position so the AI radar could take over. Successful trials of this equipment took place in October 1940, with the first production GCI radar declared operational at RAF Sopley on 1 January 1941, using the callsign was 'Starlight'.
The combination of GCI radar, AI radar and the Bristol Beaufighter developed rapidly into an effective night-fighting combination which started to inflict notable losses on enemy raids by Spring 1941.
The development of the GCI radar would spark a change in the controller's role. Sector Controllers took turns to be 'GCI controllers' at the radar site, cultivating the mix of science and art needed to interpret the PPI picture and issue voice commands to place one aircraft hundreds of yards behind another - skills that our Air Ops Controllers still learn and practise today!