AS RONALD and his crew cross the North Sea on the first leg of their long journey, here is a very brief account of their vital duties in the skies over occupied Europe.
What we now know as electronic countermeasures had their beginnings in 1940 when the Luftwaffe used its ingenious Knickebein radio beam system to pinpoint and destroy Coventry. It was swiftly identified and jammed by British scientists, just as successive British systems would be neutralised by the Germans.
As Bomber Command lost more and more aircraft to night fighters, powerful radio transmitters in England were used to interfere with fighter control. The familiar jamming tone which blocked out voice transmissions was developed into speech instructions such as “fly north and await instructions” when the bomber stream was to the south, or false warnings of fog which caused night fighters to return to base. As these warnings became recognised as fake, some German crews ignored them and were lost when the fog proved to be genuine.
In early 1943 a powerful transmitter codenamed Airborne Cigar was fitted to the Lancasters of 101 Special Duties Sqn, and proved so successful that the squadron aircraft were spaced all along the bomber stream to disrupt fighter activity. There were 42 Lancasters on the squadron, so numerals were added following the identification letter: hence Ronald’s SR-N2 which was designated Nan Squared.
The work of 101 Sqn was considered so vital to the bomber offensive that its Ludford airfield was chosen as one of only 15 among Bomber Command’s scores of bases to be fitted with FIDO fog dispersal apparatus. This involved spraying petrol from a line of pipes along each side of the runway which when ignited created a tunnel through the dense fog about 300 ft wide and 200 to 300 ft high. Pictured is a 101 Sqn Lancaster landing in dense fog which had forced the closure of airfields all over England.
The operation was top secret but one operator recalled after the war: “We sat alone in a small compartment on one side of the fuselage. All I could see was the mid-upper gunner’s feet a few feet away. I had a three-inch cathode ray tube which showed the Germans’ fighter frequencies as a line across the base, and German signals appeared as blips on this line.”
When the operator, who spoke fluent German, identified a fighter controller’s transmission he switched on one of the Lancaster’s three transmitters and blocked it. The Luftwaffe controller would then change frequency but it took only seconds to tune and block the new frequency as well. The Special could introduce a variety of jamming tones, speech, or the Merlin’s mighty roar from a microphone mounted in an engine compartment. Meanwhile, the bombaimer in the nose was throwing out metallic strips of Window to reflect the radar pulses and render the fighter and ground control radars almost useless.
An obvious move was for the fighter to home onto the jamming signals, but the RAF had thought of this and switched on their transmitters only long enough to disrupt the controller’s transmissions. The Germans knew about ABC just as soon as the first aircraft was shot down and its equipment analysed, as they did for other devices such as H2S radar, IFF friend-or-foe transmitters, and Monica tail warning radar, all of which were used for homing, but they never fully overcame it and its successors.
Among the developments was a huge transmitter codenamed Jostle, carried by B17 Fortresses and Liberators which had the space and extra generating power to take it over Europe. At one stage the jamming was so successful that the Luftwaffe was reduced to using the Army’s powerful Anne-Marie broadcasting station to disguise messages as music of different types, such as playing waltzes to indicate the raiders were over Cologne, marches meaning over Berlin, classical music for Duisberg and so on. The British then jammed Anne-Marie as well.
As the day bombing offensive intensified, the Americans used British know-how to jam the radar-predicted flak which took a heavy toll especially when the bombers held a steady course on their bombing runs. (One of the major manufacturing centres for such radar equipment and proximity fuses was a city called Dresden).
One of 101 Sqn’s major operations was on D-Day, when the squadron put up 24 Lancasters in a line north of the invasion area to jam all fighter communications while the invasion fleet was crossing. Not one fighter was encountered over the landing areas but one Lancaster was lost, probably to flak.
However, the Luftwaffe found a partial solution to Window and jamming in Wilde Sau (Wild Boar). On clear nights both day and night fighters were given a free hand to enter the densely packed bomber stream, taking a grim toll until the growing force of Mosquito night fighters was able to cover every night-fighter airfield on the deadly route to Germany.
For a full description of the electronic war, may I recommend
Instruments of Darkness by Alfred Price.