[The Wireless Operator] tuned into Saint Malo and got a beacon in England. He didn’t realise. (Feldwebel Hans Lehmann, 2./KGr. 100)

In case it is necessary to adopt crude counter measures, bombing the enemy transmitters must be considered one of the best.
(Air Scientific Intelligence Report No. 10, 12 January 1941)

The RAF’s No. 80 Wing is perhaps best known for its pioneering efforts in ground-based electronic jamming and spoofing but its Wireless Intelligence Development Unit (under W/C Blucke) also deployed the antecedents of the “Wild Weasel” aircraft introduced over Vietnam by the USAAF a quarter-century later.

WIDU’s contribution to Cold Water was “Douche”, an attack on Knickebein IV and the WESER and SPREE transmitters on the Cherbourg Peninsula. The inspiration for the operation may have been two happy accidents discovered through Ultra. At 02.00 GMT on 11 October, SPREE was reported “completely destroyed” by bombardment (during Operation Medium, a combined RAF/RN operation against invasion shipping in Cherbourg). Bletchley Park’s Commander M.G. Saunders noted that “AM [Air Minstry] and AY [Admiralty] know nothing about this”, so if either force’s action destroyed SPREE it was by accident, not design. The transmitter was out of action for a month, apparently owing to a shortage of replacement equipment, before resuming operations on 10 November.

At 0600 on the 12th, Ltn. Tietze at DONAU advised that the Den Helder area had been repeatedly bombed over the last few nights and that “yesterday” HE and incendiary bombs had fallen very close to his crew’s living quarters. This appears to have been during an RAF raid on the harbour. On the 14th came an incident alarming enough for Tietze to report it to Ambleteuse within 10 minutes and for Stabsing. Dr. Fischer to follow up to Dr. Kühnhold within the hour. At 1130, a single Blenheim had dived to 150 m and released three “heavy bombs” which fell 200 m from DONAU, albeit without damaging it. The Blenheim concerned was T1871, XD/T of No. 139 Squadron whose pilot, S/L Mertens, reported dropping his bombs on a railway line near De Kooy aerodrome after a shell had damaged his aircraft. (Mertens’ crew was completed by Sgts. Miller and Mansfield; their Blenheim carried 4 x 250 lb delayed action bombs).

Clearly disconcerted by the incident, Tietze asked if Flak protection could be made available and whether the station should continue operating or be removed to a place of safety, receiving the prompt reply that no operations were expected in the near future so he should indeed take the latter course. By 16 October the “apparatus” had been moved to a safer place and instructions were sought on whether the generators should also taken off-site. Dr. Fischer proposed that “if operations from this station are important”, DONAU should have a new layout, secure against enemy attack. He wanted to put the equipment and personnel in an existing pill box and to operate from there a “simplified turntable” (the mounting for the antenna array) via a long cable. Anxieties had probably been kept alive by two parachute flares dropped over the »Kontrollstrecke« (a line of reference points for calibrating the beam) about 350 m from the station, at 0230 that morning. In the event, DONAU was relocated before it began operations. Signals showed that the Germans were very nervous about all the transmitters’ safety, describing them as “enormously important” and “most difficult to replace.” Urgent steps were taken to provide hardened accommodation for personnel, to camouflage the installations and ensure that any threatening enemy action was reported.

Ambleteuse (about 10 km. north of Boulogne) had been attacked again in the meantime: from 2200–2300 hrs. on 12 October, seven bombs had fallen about 150 m from the crew’s quarters. It was reported four days later that three light bombs had come down 300 m north of ISAR (Ambleteuse) and another three 200 m from the “company” (the signals unit’s HQ or quarters, perhaps?). Two days later, at 0830 hrs. two artillery shells landed 400 m from ISAR and there was a parachute flare over the station at 0300 on the 26th. Later that morning there were aircraft flying over, engaged by the Flak, and the cross-channel artillery was once again active. Isolated raids and hostile aircraft continued to be reported over the following days but with no indication that the station itself was ever the target. On 2 November it was ELBE’s turn, a bomb falling 200 m from the control post’s “Stake 6” (one of a set of reference markers for calibrating the beam, usually arrayed some distance from the transmitter itself).

NOTE: The Germans were nervous early on about the installations’ vulnerability to attack, an order being circulated on 30 September to submit reports on the “effects of enemy bombs, artillery etc.” since each had been built. In future there were to be daily returns of attacks on transmitters, control posts and crew quarters, including details such as the number of bombs and how far away they had fallen. At most of the locations there was nothing to relate although two heavy bombs had fallen 800 m north of ODER at 0200 GMT on 24 September. The hostile aircraft was thought to have been flying at 3000 m and there plenty of reasons for an RAF bomber to have been over the Cap Gris Nez – Boulogne area at the time, not least to attack invasion barges. Later, other stations were able to report hostile aircraft passing overhead and being engaged by the local Flak but without any actual attack developing.

On 18 October at 08.30 hours, two rounds of "enemy artillery fire" were reported landing 400 m. from ISAR (at Ambleteuse, about 10 km. north of Boulogne). British heavy artillery emplaced around Dover did shell German cross-channel batteries in the Boulogne–Wissant area but all seem to have been some kilometres from ISAR so the beam station may have been the intended target. There was another alarm at the station at 08.00 on 26 October: aircraft were passing overhead and were being heavily engaged by Flak, while "artillery activity" had begun.

NOTE: At the height of the Battle of Britain, 15 September 1940, the Luftwaffe had planned to silence these British guns, ordering Fliegerkorps VIII to move its staff "with utmost speed" into Luftflotte 2's zone, where it would be entrusted with attacks on the long-range batteries on the English south coast. A start should be made as soon as possible after obtaining targeting information from 16th Army Meanwhile, Fliegerkorps 2 was told to attack using Stukageschwader 1.

Reporting on 8 November, Group Captain E.B. Addison (OC No. 80 Wing) was dismissive of Knickebein, citing analysis of German bombing which “has so far failed to reveal any marked degree of accuracy either locating important targets or in aiming bombs at particular points.” What was more, prisoners had “frequently admitted failure to locate their bombing objectives”, all of which was taken as evidence that the Luftwaffe was not able fully to realise the potential of its navigational aids. The “river” beams were a different matter as it was becoming apparent that “the select few of KG 100” were attaining accuracies much greater than previously seen. Addison had a proposal:

If we can effectively deny the use of this device to the enemy when it is being utilised by only a few, it is to be hoped its adoption on a larger scale will be prevented.

At the same time he recognised that, compared to Knickebein, X-Gerät would present “a stiffer problem” to “our meagre ‘anti’ devices.”

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