The Chain Home radar system was made up of twenty-one coastal stations with 300-foot-high steel lattice masts. These vulnerable structures could “see” out across the sea over an arc of 120 degrees and detect aircraft at more than a hundred miles distance and, excepting very low-flying examples, read their height and direction of travel. The detection capability was seaward only; once an aircraft crossed the cost and headed inland it could no longer be tracked by the system. They could determine the range, height, bearing, and strength of a hostile raid. Once inland though, the enemy raiders had to be plotted by the members of the Observer Corps, by sight and/or sound, depending upon visibility. The Observer Corps posts covered the country and depended on the eyes, ears, and field telephones of the volunteer members to provide a vital link in the air defence/detection system of Fighter Command by day, at night, and in all weathers.
When the Chain stations picked up radar plots they were immediately passed to Fighter Command at Bentley Priory, Stanmore, where they came into the Filter Room and a filter officer checked them against information about friendlies and hostiles before passing them on to the adjoining Operations Room, which was Dowding’s control centre. There, on a twenty-four-hour basis, he could view on a large map table the exact location in the British Isles of a developing raid or one (or more) in progress. The room was staffed by the commander’s duty controller, and liaison officers in contact with the Observer Corps, Bomber and Coastal Commands, Anti-Aircraft Command (guns and searchlights), the Admiralty, and the Home Office (air raid warnings).
The principal Fighter Command groups were responsible for limited areas. For example, 11 Group covered an area from Portsmouth to the Thames Estuary; 12 Group north from the Thames Estuary to Yorkshire (the Midlands and East Anglia); 10 Group covered southwest England; and 13 Group the north of England and Scotland. The filtered radar plots were sent by Fighter Command to the fighter groups which also received Observer Corps plots direct from the Observer centres. Those running the balloon barrages were also in direct contact with the Group Operations rooms where the Group Commanders and their controllers could all simultaneously see the actual up-to-the-minute situation on the table maps in their Ops rooms. The table maps were “manned” by WAAF girls wearing headphones and wielding croupier rakes with which they moved coloured discs representing aircraft per the plots they received. The group controller in each group directed the appropriate sector station to handle each raid. The sectors represented geographical areas within each group. Of the various airfields located within each sector, one was designated the Sector station and operated its own Operations Block which housed the Ops Room proper and a D/F (Direction Finding) Room. The personnel manning the D/F Room tracked the sector’s own fighters, using radio “fixes” obtained from IFF (Identification Friend or Foe), and also referred to as ‘Pip Squeak’, an automatic transmitter fitted in all Fighter Command aircraft.
The operators in the D/F Room passed the fighter positions to the two deputy controllers in the Ops Room where two navigators immediately determined the fighters’ interception courses, passing them to the controller whose elevated dais provided him with an excellent view of the table map of his sector and the coloured discs showing the positions of the friendly and hostile aircraft, as positioned by the WAAFs with the rakes. The sector controller then directed his fighters by accurate vector to intercept the hostile raiders, using a brief code: Scramble (take off); Angels Ten (height 10,000 feet); Orbit (circle a given point);Vector One-Eight-Zero (steer course 180 degrees); Buster (full-throttle, expedite);Tally-ho (enemy sighted); Pancake (land); Bandit (enemy aircraft).
top: Air Chief Marshal Hugh Dowding, who headed RAF Fighter Command in the Battle of Britain period; above: Assisstant Section Officer Edith Heapwas a WAAF plotterand later an Intelligence Officer; below: The plotting table in the underground Ops Room of No. 11 Group, Fighter Command, at Uxbridge, November 11, 1942.
RAF Hurricane interceptors climb from their English base to engage the enemy raiders approaching from the French coast; below; an Observer Corps member at work, summer 1940.
Code-names were devised for each sector station and each fighter squadron in two-syllable words, examples being ‘Jaunty’ and ‘Lumba.’ With squadrons typically operating as twelve-aircraft tactical units, each was divided into four sections of three aircraft, with Red and Yellow in A Flight; Blue and Green in B Flight; the pilots in each section were identified as 1, 2, and 3 (i.e. Red 1 led Red Section, followed by Red 2 and Red 3).
The organization of this elaborate communications system worked as follows: from hostile target to radar station by radiomagnetic waves; from radar station to Fighter Command by telephone line; from Fighter Command to Group and Sector and from Sector Ops to the fighter pilot in the air by radio / telephone.
For years both the British and the Germans had been working independently on their own version of military radar. The British were primarily, perhaps even exclusively, interested in developing the technology for the defence of their island nation, to link coastal radar stations by telephone and radio / telephone to their defending fighter aircraft. Their long-range radar, while less sophisticated than German radar, was effectively integrated into a sound, practical air defence system. Freya, the German long-range radar, was capable of detecting hostile aircraft to a range of seventy-five miles and through a 360 degree circle, though it could not detect altitude. And, unlike the British radar which incorporated gigantic fixed steel lattice masts, Freya was mobile. In their Wurzburg short-range radar, the Germans had developed a relatively small, completely mobile apparatus for accurate detection, especially in aid of anti-aircraft guns and searchlights. It was the Wurzburg system to which he was referring when Hermann Goering famously remarked, “If a single enemy bomber crosses our frontier, you can call me Meier”
The Germans had been curious and intrigued by the continuing construction of huge masts along the south and east English coasts in 1939. Assuming the high masts were part of a new radio system, they decided to learn all they could about what the British were up to in those lengthy construction projects. While they undoubtedly discovered some of what they wanted to know through the use of spies, they also employed a somewhat more elegant approach when they sent the great airship Graf Zeppelin across the Channel, fitted out with cameras and electronic detection equipment for a spot of aerial reconnaissance.
With the Luftwaffe Signals Section chief General Wolfgang Martini on board, the airship cruised leisurely up the east coast in late May, Martini and the crew unaware that they were being plotted throughout their journey by the very radar stations they had come over to observe, and those Zeppelin plots were with the controller at Fighter Command. The reconnaissance mission came to nothing and, in the evening of 2 August, only a month before the onset of war between Britain and Germany, the Graf Zeppelin set out again in the darkness, the crew hopeful of making a breakthrough discovery of what the British were up to along those high cliffs. Again, the recce came to nothing more than to kindle the amusement of two patrolling RAF fighter pilots and that of the coast guardsmen near Aberdeen.
Quite soon, the British Chain Home radar system would be completed and would figure dramatically in the outcome of history’s first great battle in the air.
Pilots of 19 Squadron on their Duxford, England base in 1940.