A remarkable story was unfolded by the Signals Directorate of the Air Ministry at the close of 1945 of how Bomber Command fought and won the war in the ether. The R.A.F.'s objectives were the Luftwaffe's radio communications and the enemy radar – the radio “eye” which can detect and position approaching aircraft. The intention was to reduce this enemy intelligence to chaos.
Radio counter-measures, as they are called, were first considered in 1941, and in 1942 it became feasible to employ them in Bomber operations. From then until the end of the War this extremely complicated and abstruse subject became the wholetime study of a small number of specialists who alone understood all its ramifications.
The most spectacular of these radio counter-measures introduced itself over Hamburg on the night of July 24-25, 1943, when a vast number of aluminium foil strips fluttered slowly down from our bombers, to settle on the city. This was operation “Window”.
Each of the 791 bombers employed on the Hamburg raid dropped (in addition to its bombs) one bundle of 2,000 of these foil strips every minute, which mounted to 2½ million strips weighing 20 tons. Assuming that each bundle showed an echo for 15 minutes, the total number of echoes on the enemy's screens during the raid represented 12,000 aircraft.
Side by side with our enemy radar offensive was the determined effort to upset enemy radio communications operated by the Luftwaffe. This mostly took the form of “jamming”, or obliterating an enemy signal with a more powerful one of our own on the same frequency. A variation was the use of German-speaking W.A.A.F. Broadcasting from the U.K. On Luftwaffe frequencies, giving false information and counter-orders.
In the summer of 1941 it was established that the enemy were using radar to plot our bombers for fighter interception. Calculations gave the experts its approximate position, and in December 1941 aerial photographs were obtained which led to our raid on Bruneval on February 27, 1942. It was the knowledge gained from the capture of German apparatus there that made possible the development of our counter-measures, two of which – code names “Tinsel” and “Mandrel” - were introduced in December 1942 and were an immediate success.
Developed at the Royal Aircraft Establishment at Farnborough, “Tinsel” made use of a radio-telephone transmitter with the microphone placed in the engine or in the aircraft's fuselage. Each operator was given a specified frequency band to watch with instructions to “jam” any German radio telephone he heard, and the noise the German pilot heard from our aircraft may be imagined. Every wireless operator in each bomber took part. They were trained with the help of gramophone recordings of actual night-fighter radio traffic. Valuable help came from the German-speaking operators distributed through the bomber force and from many of the Polish squadrons came a stream of valuable information as to enemy reactions to the jamming.
The intention with “Mandrel” was to jam the enemy's early warning system, the idea being that if his fighter reaction against the raid could be delayed only 20 minutes a very great advantage would be gained. Associated with this were a number of high-powered ground jammers sited along the South Coast which were intended to blind the German stations across the Channel. On the night of April 26-27, 1943, a high-powered wireless transmitter with a narrow beam-operation, code name “Ground Grocer”, was established at Dunwich on the East Anglian coast, and to judge from remarks heard coming from German pilots was an immediate success. A second transmitter was later established at Deal, Kent.
The Germans found themselves forced to use very high frequencies for their communications; and jamming equipment for this was installed at Sizewell on the East Anglian coast. This produced enough noise in the enemy earphones to prevent effective control of their fighters over the Dutch coast and farther west. The operation began work on the night of July 30-31, 1943, under the title of “Ground Cigar” and remained in operation until September 17, 1944. Range limitation was an obvious objection to this, however, except as an interim measure. What was wanted was airborne equipment which would carry the jamming right into enemy territory, thus protecting aircraft of Bomber Command over the whole route to and from the target.
More investigation followed, new equipment was designed and the decision was made to equip a normal 3-flight Lancaster bombing squadron (No. 101). It was first used operationally on the night of October 7-8, 1943, in No. 1 Group, with jamming apparatus, when each aircraft carried a trained German-speaking operator as an additional crew member, whose duty it was to find and jam enemy frequencies. A normal bomb load less the weight of the operator and the equipment was also carried.
Five months had elapsed during that year before fitted aircraft were ready for the Squadron. The type of jamming is best described as a “wig-wog” noise which produced a constantly varying audible note running up and down the scale on the speech channel that was to be jammed. The receiver was an ingenious piece of equipment, specially designed for its purpose and quite unlike anything before fitted in an aircraft.
So successful was this system that the Germans were forced to use Morse telegraphy in an attempt to break through. They tried speeding up their radio-telephone messages, switching on their transmitters for only a few seconds at a time, without success. Yet another subterfuge was to transmit a continuous musical programme, breaking off suddenly to snap out an order. “Airborne Cigar” (or A.B.C., as it became known) was operated by No. 101 Squadron from October 7-8 1943, to April 19-20, 1945.
The B.B.C., the General Post Office, and Cable and Wireless, joined in the “Corona” system which was to be used as a means of confusing, distracting and annoying the enemy, even to the extent of giving the German fighters instructions contrary to those which they received from their own ground controllers. Instead of transmitting “noise”, as was the case with the ordinary “jamming” tactics, it was decided to use a “ghost voice” – a fluent German speaker. This was heard by the enemy for the first time on the night of October 22-23, 1943.
The target on this occasion was Kassel, and before the end of the raid there was chaos in the enemy night defence organization. A furious German ground controller was warning his aircraft to “beware of another voice” and “not to be led astray by the enemy”. The “voice” not only spoke idiomatic German but could also mimic perfectly the voices of his opposite numbers. After a particularly violent outburst by the German controller, the “voice” said: “The Englishman is now swearing.” The German's reply was “It is not the Englishman who is swearing by me!”
There were many more radio devices used to counteract, the enemy's frantic attempts to control the Luftwaffe fighters. Often this meant quick thinking on the part of the R.A.F. technicians who were always one jump ahead of the Germans. Right up to D-Day our technical resources were engaged in a tense fight to keep our bomber losses down to an average maximum of five per cent which was achieved.
An early attempt to deal with enemy radar by use of a warning receiver was christened “Boozer”. In its original form it was simply a receiver which lit a warning lamp when the aircraft became “illuminated” by an enemy radar transmitter. The pilot changed his course until the lamp went out.
Operation “Drumstick” jammed enemy high frequency telegraph controls in the 3.0-6.0 megacycle band. “Fidget” jammed enemy telegraph commentaries and instructions to night fighters during the progress of a Bomber Command attack on the medium waveband. Enemy ground radar stations using the 300-600 megacycle band were jammed by operation “Carpet”. And “Jostle” was a high-power high-altitude jammer of enemy radio-telephone communications on short and ultra short wavebands. It was in fact a flying broadcasting station, 40 times more powerful than the transmitters usually carried in aircraft.
One more device was known as “Piperack”, which jammed enemy radar on the 95-210 megacycle range. With all these devices, not only was the enemy pursued with unfailing vigour but radio countermeasures in Bomber Command paid a dividend out of all proportion to the capital, in terms of effort, which was invested in it.