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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”.

In London on 25 July, a minute on the current position in Malta was submitted by the Assistant Chief of the Air Staff (Intelligence) to his counterpart for Operations. Jamming of RDF and fighter R/T was only affecting Malta but was expected soon to appear wherever the Luftwaffe was attacking the Mediterranean theatre. Ground jammers were thought to be active in the Licata and Pozzolo areas of Sicily. Airborne jammers, meanwhile, “if not already operating over Malta”, are almost certainly to be used by Fliegerkorps X against the Suez area”. This was the Germans’ first known attempt to disrupt RAF night fighting by jamming, “and it suggests that they are using Malta as an experimental testing ground”. It was important “that no clue be given to the enemy as to the success of his efforts” and so affected radars should not be switched off (ULTRA had dislosed that this was being monitored, see above) or express any concern over voice channels).

Multiple raids on Malta were planned for 27 July. Among these was a KG 54 operation by evening twilight against the dispersals at Ta’Kali. This would be supported by the Caruso-Ju 88(s) and the “signals jamming plane”, the latter escorted by a pair of Bf 109s from JG 53 for as long as there was still light. The night of the 28/29th would see six Italian Ju 87s sent to Hal Far while another three were to bomb “enemy radio sets” (probably radar stations) in the hour before midnight. These efforts would be supported by Noto and the “KG 54 signals plane”. For the 30th/31st the Fliegerkorps specified that KG 54 should support Italian bombers with two Caruso-Ju 88s while the following night it was KG 77 providing two such machines.

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. Oberleutnant Hans-Dieter Haffner’s Ju 88 of 4./LG 1 (W.Nr. 140736, L1+IM) was shot down about 112 km west of Cairo during these attacks. Two of the crew survived and their interrogators 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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