One of two He 111 detailed for ASV jamming on 22 September took off at 1615 and two more operated the next night, one taking off at 1649; they landed at 0030 and 0530 hours. These machines had been protecting the tanker Rondine, as was a lone Do 217 night fighter which had started at 2100 hours. El Daba meanwhile had been ordered to jam GCI radars in the Nile Delta for two hours from 1800. Early on the 23rd, the WIM-Zentrale had advised its sub-stations that a calibration flight would take place from 0600 hours with selected frequencies being jammed in succession:
That night, two He 111 operated on convoy protection, from 1640–0032 and 2029–0552, jamming three frequencies while for its part Crete-West was transmitting from 1855, jamming no fewer than eight wavelengths. A “signals Junkers” (probably a Ju 52) was due in Benghazi on the 24th to work with existing aircraft reporting services, providing an R/T relay for the fighters based there, and on the following day Ju 52 NR+AE flew between Heraklion and Kalamaki. That morning, the Middle East Y-Service signalled the Air Ministry as follows: “Probable that P4 BA and DA ASV jammers (Query Wildschwein).” This particular hypothesis was mistaken since P4 was the unit code of Fl.Kps. X’s Führungskette (HQ flight). Also, WIM 8 reported that its western sections were being fenced round with barbed wire, work expected to take two or three days.
Next day an He 111 took off at 1630 to provide ASV jamming cover for an Axis convoy and a second left two hours later, both landing in Heraklion. Once again Do 217 night fighters had joined in escorting the ships. On the 27th a Fw. Pradel notified the Bardia WIM station of the expected movements of KF+UX (W.Nr. 3074), a signals Ju 52 associated in June with Luftnachrichten Abteilung Afrika. Overnight convoy protection on 27 September was provided by three ASV jamming aircraft (one of them up at 1600), a Do 217 which left Heraklion at 1845 and another from Derna at 1930 hours. Of these night fighters, one was over the convoy from 2015–2140 then lost contact with it; the second landed at 2030 with engine trouble. Three Beauforts were subjected to jamming while operating against a convoy WSW of Crete on 27 September, such that none of them got an ASV contact and only one a visual. Three were three He 111 jammers on convoy duty that night.
On 29 September, the Air Ministry was warning the RAF in the Middle East that Freya and WIM stations were to cooperate in tracking Allied reconnaissance aircraft, immediately passing their plots to fighter and Zerstörer units. The object was, of course, to protect the supply convoys, and efforts would concentrate on the sea areas north of El Daba and in an arc off the western tip of Crete, both lying within Freya coverage. Fliegerkorps X reported its strength on the 30th, not mentioning Kdo. Koch but including “two unspecified units, strength unknown” and a Nachtjagdkommando with 4 (0) aircraft, presumably including the Do 217s. The Korps planned a single He 111 jamming sortie that night and this was duly carried out from 1540–2030.
By the end of the month, Air HQ Egypt had issued a set of instructions for the “Control of ‘Lark’ Fighters”, setting out how jamming aircraft were to be countered:
The apparatus works through the V.H.F. set by means of special aerials. When these are switched on the pilot can D/F himself onto any aircraft giving out a transmission.
At present the gauge altitude from the apparatus. He may be able to get some assistance re altitude from his A.I. but this is usually jammed when close to and behind a “Lark” bandit.
The range is about seventy miles. Initial vectors are given to the fighter not to get a contact, but to save time and distance and to avoid a long stern chase …
When a “Lark” is reported and the probable “Lark” bandit established, Sector will give the fighter a vector to cut off the bandit. If possible they will give the height and course of the bandit and its distance from the fighter.
When the fighter is nearing the bandit and it is thought that the interception cannot be assisted by further vectors, the pilot will be told to go over the Channel “C”. He will then switch on the apparatus and complete the interception himself …
It had been concluded by 2 October that the enemy might not use “Lark” throughout a raid but only intermittently, for example during an attempted AI interception:
The “FLYCATCHER” Beaufighters must, therefore, be given first priority under G.C.I. control unless it is established that the enemy are using “LARK” continuously.
Measures were also underway to increase ground radars’ resistance to jamming and a standard format had been developed for the stations to report times, frequencies, bearings etc.
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