How Our Defence System Worked
This communications network linking the component parts of the system would prove to be of vital importance to UK air defence in 1940. This is most easily explained by looking at how the system worked in wartime. By the time the Battle of Britain began, the Luftwaffe’s bases were far closer to the UK than they had been at the start of the War. A German fighter squadron based in the Pas de Calais could cross the Straits of Dover in just six minutes. However, the German bombers were based further inland and, heavily laden with bombs and fuel, they had to climb slowly to their operational altitude. The German Messerschmitt 109 fighters were handicapped by their relatively short endurance, which is why they were based further forward on aerodromes near the coast. There, they would wait for the bombers to approach before taking off and joining up into much larger formations.
This process took a little time and, as the formations assembled, they began to appear on British radar screens. This generally provided about twenty minutes warning of their approach. The radar station would report the raid through constantly open telephone lines to Bentley Priory, where the plots were received in a “filter room” and placed in the appropriate map square on the filter room map table. The function of this room was literally to filter the plots, combining those from different radars and weeding out extraneous returns, which might be flocks of geese or meteorological phenomena. When the filter officer was sure that a plot was genuine, he allocated it a hostile raid number and a “Teller” would speak into her microphone [most were women of the Women’s Auxiliary Air Force] and pass the details of the hostile raid plot. Her words would simultaneously echo in the headphones of WAAF “Plotters” in every operations room in the affected region, from Fighter Command at Bentley Priory right down to the Group and Sector levels. Instantly and simultaneously, the “Plotters” would place the appropriate plot counter in the correct map square on all the operations room map tables throughout the system. From the first radar contact to the operations room plot appearing, this process took about four minutes.
There were now some sixteen minutes left, but it took a Spitfire squadron in a battle climb some fourteen minutes to reach twenty thousand feet and a Hurricane squadron a few minutes longer. So the controllers at the Group Headquarters, who determined which fighter squadrons were to be scrambled to intercept incoming raids, had very little time to make the right decision if they were to intercept. As the radars tracked the raid, the Plotters moved the counters across the map table using croupier rakes; as in Ashmore’s LADA, the arrows showing the track were colour-coded according to the colour on the face of the segmented clock in the operations room. Plots older than fifteen minutes were removed from the table.
Once his mind was made up, the controller at the responsible Group headquarters would lift his phone and tell the switchboard operator to connect him to the relevant Sector station. The Sector controller’s phone would ring and he would hear the Group controller’s voice issuing instructions to scramble the relevant squadrons and confirming the altitude at which they should patrol, and the patrol area. The orders were crisp and to the point, wasting few words. Thus, “Scramble 92 and 72, Patrol Canterbury, Angels 25”, meant 92 and 72 Squadrons were to be sent into the air immediately and were to climb to 25,000 feet and form a patrol line over the city of Canterbury.
The Sector controller repeated the words to ensure they were correctly understood and then put the phone down. Hethen turned to the phone connected directly to the squadron dispersal huts on the airfield. When the phones in the dispersal huts rang, every pilot lazing in the bunks in the hut, or outside in deck chairs, or on the grass, sat bolt upright and stared at the individual who lifted the receiver. As soon as he shouted “Scramble” they ran towards their aircraft. Parachutes would have been placed on the wing or the seat, and the ground crew, who never strayed far from their charges, helped the pilots buckle them on, slip into their cockpits and do up their straps. Then the engines all around the dispersal spluttered and roared into life, brakes were released and the aircraft began to move, bouncing and rolling across the grass in a pell-mell race to get airborne.
Once the aircraft left the ground, the fighter leader called up the Sector controller for instructions. It was then the Sector controller’s task to direct them towards the enemy via radiotelephone, his initial order being the course to steer together with “Make Angels 25”. As more information was received on the strength and direction of the raid, he would pass this to the squadrons and change the vectors as necessary to bring them over Canterbury or adjust their course to meet the enemy. All tracking of raids that had crossed the English coast was the responsibility of the Observer Corps, as the radars looked out to sea but not inland. The margins for error were small, but the vital communications links between the component parts of the system allowed just enough time for the defences to react.
Thus the radars, Observer Corps and the filter and operations rooms gathered, filtered, disseminated and displayed the information in usable form. But they made up only those elements of the air defence system designed to tell commanders what was going on. Moreover, while the commanders benefited immeasurably from this heightened situational awareness, they had still to decide what resources to use, despatch those forces to intercept, and manoeuvre them into contact with the enemy, which was no mean feat in a fast-moving three dimensional battle. And, once battle was joined, it had to be won. Fortunately, whilst in charge of R&D for the RAF in the mid-1930s, Sir Hugh Dowding had also approved the development of fast monoplane fighters with eight machine guns in the wings, enclosed cockpits and retractable undercarriages – the immortal Hurricane and Spitfire – which replaced the obsolete biplane fighters, such as the Gloster Gauntlet, which still equipped many squadrons in 1938. The first squadron to re-equip with the Hurricane was 111 Squadron, based at Northolt, in January of that year. The first Spitfire to enter squadron service was delivered to 19 Squadron at Duxford on 4 August 1938, barely a year before war broke out.