The Chairman opened the discussion by saying that the enemy operation in the Straits of Dover on 12th February 1942 was supported by intentional jamming of R.D.F. Stations.
Minutes of Air Ministry meeting, 23 February 1942
The February 1942 withdrawal of Scharnhorst, Gneisenau and Prinz Eugen from Brest to home waters (Unternehmen Cerberus or—to the British—“The Channel Dash”) was supported by a combined programme of earthbound and airborne jamming. On 5 February, Marine-Gruppenkommando West had advised Luftflotte 3 of its belief that the ships could pass undetected during the hours of darkness and that to begin fighter escort and RDF jamming at daybreak would just alert the British: “it has been astablished beyond dispute that every activiation of jamming devices is immediately be recognised by the enemy”. Unless the ships were spotted sooner, jamming should commence abruptly when the formation was off Fécamp. Therefore the Navy requested that the Luftwaffe jamming organisation around Cherbourg should come into action if the British were already known to have been alerted, otherwise it start operate only when the jammers covering the Dover Straits came on. After discussing all this, it was agreed next day that jamming in the Straits would go ahead as the Navy suggested. The airmen would however direct what happened at Cherbourg in view of IX. Fliegerkorps’ planned diversionary raids against the English mainland on the first morning. Duties were allocated as follows:
Jamming of English Air Force and Naval locating devices
1.) Luftflotte 3 is to prepare for the jamming of English Air Force sets:
a.) for the sector Brighton – Lyme Bay.
b.) for the sector Isle of Wight – Clacton on Sea.
2.) Mar. Gruppe West is to prepare for the jamming of English sea-targeting sets with the mephasis on the western part of the Straits.
3.) The jamming operation will take place according to the situation, in agreement with Luftflotte 3.
Cerberus appears to have been the first time the Luftwaffe attempted jamming from aircraft and the Kriegsmarine Operations Staff diary (as translated postwar) says that:
The bombers of the IX. [Fliegerkorps] accomplished the following:
One plane sent out deceptive radio traffic.
15 planes staged feint attacks in the area northwest of Brest in order to tie down enemy fighters In the area of southwestern England.
10 planes attacked airfields and harbours.
IIn addition to the above, historian and veteran of the Luftwaffe signals branch, Fritz Trenkle (1920–1996) stated that two He 111 had taken off from Évreux before dawn on the 12th to fly parallel to the coast of Southern England. They belonged to the Funk-Technisches Untersuchungskommando (Radio-technical investigation detachment) LC 4, and each was fitted with five Garmisch-Partenkirchen transmitters. Named after a Bavarian ski resort, these were intended to produce multiple false echoes on British radars. More such spoofing was provided by ground-based Breslau transmitters while a 15-strong feint by III./KG 2 aimed further to confuse and disperse the RAF’s fighters. The Kriegsmarine’s chronology of the operation includes the following:
12.50 [GMT+2] Cap Griz Nez was passed. Planned jamming of enemy radars began at 1000 and appeared fully effective at first. Own location of formation from »Ozet« [Ortungszentrale?] Channel Coast achieved continually between 1000 and 1500.
The following decrypts relate to listening and jamming in support of Cerberus during the morning of 12 February:
The night of 12/13 brought a further report of jamming, from Wellington Z8802 which was operating from Bircham Newton in search of Scharnhorst, Gneisenau and Prinz Eugen off the Dutch coast and experienced interference on its ASV Mk. II. By 2 March, Coastal Comamnd had issued instructions for the recording and reporting of all suspected jamming of its “special equipment”.
At the Air Ministry meeting on 23 February, it was noted that the jamming had lasted from 09.30–19.30 and “affected to a lesser or greater degree all types of R.D.F. stations” other than those operating on 10 and 50 cm wavelengths. It had been “of a better type than experienced previously but could not be regarded as a very good attempt”. In the Telcommunications Research Establishment’s view the jamming would have been more effective if—among other things—“interference had been radiated from the air”. The airborne contribution had not been recognised, the trouble was thought to have emanated from Saint-Inglevert in the Pas-de-Calais.
"Radiolocation", 1941 British Army recruiting poster. (National Army Museum)