On 20 July, a Malta-based naval aircraft had reported jamming of its ASV but the Admiralty was unable to confirm that this was deliberate, suggesting it may have fallen foul of transmissions directed at RDF stations onshore. The same day, Fliegerkorps X in Greece had been asked to approve the transfer of a “signals Ju” marked WT+AO to Tobruk next day with the early morning convoy, to work with NJG 2 whose Signals Officer, Ltn. Schulz, would provide instructions. After an operation in collaboration with the night fighters, it was to land in Crete although personnel and equipment would remain in Tobruk. The next night a Malta-based Beaufighter chased a jamming aircraft, the RAF pilot reporting that the interference became a very high pitched whistle, its strength increasing until it was impossible to receive directions from his ground controller. Reviewing the position on 22 July, Air Commodore Arthur Lee urged that:
… we should aim at having one or two bomber aircraft with each raid capable of jamming enemy main chain and gun control RDF … the time has arrived when we should be in a position both to counter jamming by the enemy and also to jam his RDF and R/T more effectively.
Reporting to the Air Ministry on the 23rd, Malta submitted a technical analysis of the signals from Sicily, noting that the transmitters were capable of changing frequency rapidly and that the enemy was continuously monitoring the AI waveband. Jamming of AI was “very effective when on frequency” while that directed against VHF was “… definitely airborne. Nature not repeat not yet known”.
On the night of the 31st, the aerodrome at Heliopolis, Cairo was raided by six He 111 of KG 100 and 13 Ju 88 of LG 1; three of the former and six of the latter carried Caruso. This was the first time that jamming had been encountered by the RAF in Egypt:
Enemy aircraft raiding Alexandria and Cairo areas night of 31/7 carried jamming devices which affected COL [Chain Overseas Low], GCI and VHF and to a lesser extent AI … Suspect several aircraft carried jammers on different frequencies [and] that jammers were on when aircraft were in Fuka area and were kept on until they returned there.
Chief Signals Officer, RAF Middle East
Group Captain Colin Cadell of the Air Ministry’s Signals and Wireless Intelligence Section noted that no jamming of either ground or airborne radars had been reported by the defenders but he asked his counterparts in the Middle East to confirm this. A Ju 88 of 4./LG 1 was shot down about 112 km west of Cairo during these attacks and interrogation of a survivor elicited the information that “they carried no jamming apparatus for use against our warning system nor detector apparatus against night fighters”. However, when a 6. Staffel Ju 88 A-4 came down at El Amariya in the early hours of 31 August, crew members revealed that during the preceding week a Staffelkapitän had told his men that all bombers were to be fitted with “night fighter detector apparatus similar to that used by the RAF”.
Meanwhile, U-boat Command had asked whether Allied search aircraft might be countered by jamming stations set up on the French and Spanish Biscay coasts. This was rejected on the grounds that available sets had too short a range. It may be that the crucial difference in the Mediterranean was the number of islands on which the jammers could be sited to extend coverage along the shipping routes. A review by the Telecommunications Research Establishment (TRE) of jamming in Britain and home waters between February and July concluded that: “There is still no evidence of airborne jammers or of special AI ground jammers and no real evidence of intentional interference with ASV”.
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