From the night of 5/6 July onward, traffic was picked up disclosing overnight maritime surveillance (Überwachungsflug in German messages) by radar-carrying Fw 200s of KG 40. It certainly made sense for the Germans to be watching Biscay by night as well as by day, for the safety of U-boats on passage as well as their own surface units. Among the aircraft whose signals were picked up was “D”, factory marking CE+IO (Fw 200 C-4, W.Nr. 0150). The 13th saw the Cheadle intercept station picking up on “unusual activity from the Bordeaux area”, some form of exercise involving a ship, a plotting station, an aircraft and its ground controller. Although the aircraft was off Royan at midday, the ship had still not sailed over three hours later.
On the night of the 15/16th, aircraft “A” was active west of La Rochelle after taking off at midnight but turned back inside the hour after reporting — in plain language, because it had no code book aboard — a defective “HTL” (Hohentwiel radar). A nine-hour sortie from 1945 on the 20th was attributed to III./KG 40 however. Shorter night flights with radar also took place, some attributed to exercises. In Britain this was noted as “the first direct evidence of ASV being fitted in Fw 200 aircraft in the Western area”. The unit concerned was thought to have been the 2. Staffel which had been withdrawn from operations at the end of May for, it was thought, re-equipment/retraining.
Meanwhile, the Kriegsmarine was introducing new monitoring receivers but for the time being only prototypes were available, with just two sets expected during July. There was an “ASV Flight” by one aircraft on the night of 30/31 July, the machine being told in the early hours to land at Cognac rather than Bordeaux. When the first overnight operation by an He 111 was noted, on 31 July, it too was thought to involve Air-to-Surface-Vessel radar (times given are GMT + 2 hours):
Meanwhile, the Kriegsmarine was introducing new monitoring receivers but for the time being only prototypes were available, with just two sets expected during July..
At the end of July, the submarines were directed to make only sparing use of "Metox" for fear that Allied aircraft were homing on its emissions. An inspired piece of misinformation from a prisoner “confirmed” this suspicion and by 12 August boats had been told to stop using it altogether. However U-161, the first with the new “Hagenuk” warning receiver, had sailed four days earlier and the device had worked perfectly all the way across Biscay:
On 13 August an He 111 was to leave Bordeaux at 2000, cross the coast 10 minutes later, return north of Cap Ferret at 0350 and land at 0400. Meanwhile, an Fw 200 was to take off from the same aerodrome at 2015 and fly south along the coast for 100 km, dropping flares from 4000 m before returning home at 2300. The same day, an Fw 200 (W.Nr. 0221, F8+IT) made contact with convoy SL 134 but was damaged by a Liberator and began to lose fuel. The pilot, Obltn. Günther Seide, was ordered to make for Spain and to jettison its “secret apparatus” (probably Hohentwiel). The aircraft reported that this had been done and, six minutes later, that it was landing at La Coruña.
Two machines were again active on the night of the 16/17th, one giving an estimated landing time of 0300 and the other “evidently returning in the early hours.” Presumably on the basis of call signs, the first of these was thought to be the Heinkel from three nights previously while the second was F8+AD (Fw 200 C-6, W.Nr. 0218) of Stab III./KG 40. The night of the 19th brought another Fw 200 flare-dropping sortie, over the bay off Arcachon and lasting two hours; the aircraft on this occasion was thought to be TA+ME (Fw 200 C-5, W.Nr. 203).
It was 24 August before another planned He 111 flight was announced, leaving Bordeaux at 2040 and returning north of Cap Ferret just over three hours later. At just over three hours, this was an unusually short sortie and, as was so often the case, no W/T traffic was intercepted to confirm that it took place. An operation six nights later was due to begin at 2100 and the He 111 contacted control, apparently preparatory to landing, at 0540. This was described by Bletchley Park’s Naval Section as “ASV flight by III./KG 40, Bordeaux with 1 He 111.”
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