The RAF in Egypt had fielded a “special Hurricane” (at Idku with No. 46 Squadron) and at least two “special anti-jamming Beaufighters” which it hoped could locate and engage the “Larks”. The special Hurricane was fitted with a limiter on its V.H.F. set “which is an antidote to the jamming interference”, leaving it “possible to communicate with the aircraft under ‘Lark’ conditions”. Although still useable as a normal “catseye” fighter it was not intended that the Hurricane should try to intercept jammers, rather it was to test V.H.F. in the face of interference. Special Beaufighters had also been been flown out from England and handed over to 89’s Malta detachment but there were insufficient ground crews on the island to service them, so Air HQ Egypt was ordered to send the necessary personnel as soon as possible. On 24 August, Egypt advised Malta that three sets of VHF homing aerials and ancillary gear had arrived and were being fitted into Beaufighters of No. 89 Squadron there. (Two days later, No. 89’s F/L J. Waddington and P/O A.B. Carruthers took up X7715 on a “special equipment test”). So far as practical, these aircraft were to be reserved for operations against airborne jammers and a procedure for interceptions was outlined, based on ground stations’ fixes on the jamming source. It was expected that this would be modified in the light of experience, however:
Those concerned are reminded that the subject of jamming is a highly secret nature. It is not to be discussed more than is absolutely essential, and controllers are warned particularly against making any reference to [it] on the R/T.
During August and September, 89 Squadron’s CO, W/C George Stainforth and F/L J.E. Fynn of AHQ Egypt made a number of flights to test the homing aerials. The pilot homed on signals heard over the aircraft’s radio, which had to be modified so the operator could reduce their volume to a tolerable level. As the interceptor neared its target the sound changed as the signal overloaded the receiver “which proved most useful in practice”; switching between upper and lower aerials also gave an indication of whether the “Lark” was above or below the Beaufighter. The trials suggested that the system should be capable of bringing a fighter in from 80–110 km to visual range (about 150 m below the target) without assistance from the ground. Within the squadron, this activity was called “Raspberry” to avoid overuse of the “the most Secret code word LARK”. (Similarly, Coastal Command’s reporting word for jamming was “Daisy”). COL stations in Egypt experiencing or suspecting jamming were ordered on 28 August to pass the codeword “RAINBOW” to the Controller at No. 252 Wing. If it was his assessment that a raid was developing or in progress over the Nile Delta, then he was to refer the alert up the chain of command, so that No. 260 AMES (= Air Ministry Experimental Station = radar station) might stand by to take over control of defending fighters. It was strictly forbidden to use the word “jamming” over the telephone.
By early November however, the defending “special” fighters were also being referred to as “lark aircraft” while the threat to Egypt was so far diminished that only one of them was being held at 30 minutes’ readiness, at RAF Abu Sueir. By that time, “to avoid a certain amount of confusion”, the following standard terminology had been specified:
Back in Britain on 31 August, TRE issued a report of trials conducted over Shropshire deploying Beaufighters equipped with AI Mk. IV or a Mk.IV/Mk. VII combination against friendly aircraft transmitting a jamming signal. A 30W continuous wave transmission was found to have a range of about 193 km against the Mk. IV set. The paper observed that: “One method of dealing with such airborne jamming is to shoot down the aircraft concerned” and went on to explore ways of doing so. Interestingly the TRE report does not make any allusion to contemporary developments in the Mediterranean, rather it addresses the possibility that the Germans might want to extend their jamming coverage beyond the limited range of their ground installations along the Channel coast.