Conclusions

That so much of the Bletchley’s CX/JQ report from 14 November is given over to interpreting Y-Service material appears to be because analysts currently had very little of their own and were keeping busy until the Luftwaffe’s keys could again be broken. Ultra had nothing to say about the coming night’s attacks—such warnings as it had been able to provide had all been given by the early hours of the 12th.

The deciphered information on the beam alignments for Wolverhampton, Birmingham and Coventry was a major clue, the more so when combined rvjoneswith Probst’s revelations. The identification of the targets from the figures was not undertaken at Bletchley however; Dr. R.V. Jones of Air Intelligence writes that he plotted the bearings.

The numbers 1, 2, 3 and 4 on the captured I. Fliegerkorps map had misled the RAF in their efforts to identify Moonlight Sonata’s target(s). This is understandable since the various Intelligence branches had no reason to trust one talkative and comparatively low-ranking prisoner more than documentary evidence. The nature of the misunderstanding is clear from call sign F4GD’s reports from the skies over Coventry of bombs in target areas 1 and 3—the numbers denoted parts of that city.

Should Ultra’s KORN have been recognised as Coventry? Although the Germans did not always “disguise” their targets so thinly, PAULA had been identified as Paris on 31 May and LOGE had likewise been recognised as London well before the Mondschein Sonate signal while on 22 June, Bletchley had commented on a German message about a planned "Undertaking [i.e.Unternehmen] Strassburg":

Considering the German habit in Norway of using Decknamen [cover names] beginning with the same letter such as OLDENBURG for OSLO, BREMEN for BERGEN etc., “undertaking STRASSBURG” may be not unconnected with the tender interest shown by the Germans in SOUTHAMPTON [in a signal of 10.30 hrs. on 21 June].

When it comes to interpreting KORN, Britain is lacking in towns whose names begin “Ko…”; conversely the German language has few if any nouns beginning “Co…” so “Ko…” is the obvious substitute (just as English renders Köln and Koblenz as Cologne and Coblenz). The choice of UK industrial or population centres beginning with “Co…” is limited but might include Colchester, Consett (then home to a major steelworks but probably out of range of the German beams), Corby and Coventry.

With all that, it would not have been that great a leap to make the KORN = Coventry connection but the documents do not suggest that this was done before the raid and indeed the identification was still only tentative in a decrypt produced the following night. This was a part of a report on British AA defences and decoy sites from Bristol through the Midlands, based on observations by Luftwaffe aircrew:

… On 12–13/11 at “BILD” heavy AA fire, well-directed. At “KORN” (? Coventry …) heavy AA fire, more concentrated E. than W. of the city …

On 29–30/10 at KORN were 2 dummy fires in the city area, which flare up when approached. On 27–28/10, 10 km. N. of KORN, a dummy blast-furnace.

To confuse matters, when Southampton was blitzed on 30 November, Aschenbrenner’s aircraft sent two signals:

18.12 GMT: “Korn 8 large fires”

18.18 GMT: “Korn 20 large fires”

So, after the success of Moonlight Sonata, was “Korn” used to mean “target area” or “aiming point”?

Communication between intelligence agencies was another issue, Dr. R.V. Jones has written that he had not seen Felkin’s report on the revelations made by Ltn. Probst. Further, a Bletchley Park officer wrote to his Director on 16 November:

You will have observed that the breaking performed by Hut 6 is becoming increasingly difficult.

blandy1He complained that his team was not seeing the RAF’s data on beam frequencies, bearings and times of operation, any of which would have served as valuable “cribs” for breaking “Brown”, the key used by the beam stations. The Y-Service’s Gp. Capt. L.F. Blandy apparently believed that external information would “contaminate” the decrypts and Bletchley was at pains to stress that it wanted the material “for breaking and not intelligence purposes.” Evidence from prisoner interrogations was also requested.

In a subsequent Hut 3 paper, these deficiencies are restated and are annotated “Nothing done 20/12.” Perhaps in an attempt to goad the Air Ministry into co-operation, the paper’s author notes that by contrast:

… the Admiralty makes a point of supplying the German Naval Section of GC&CS with every item of information available.

The 31 December memo from Hut 3 indicates that information flowed from Bletchley to No. 80 Wing but not in the other direction. They did not know what, if anything, was done with the intelligence they produced.

Bletchley also had problems of capacity and was certain that it could achieve much more if these were remedied. On 20 November an unsigned paper had lamented that:

The present situation is deplorable. Our two Spiders [improved Bombes] are working continuously and do not get the constant attention that they need. They cannot even deal with Red and Brown [Luftwaffe ciphers], so the Naval work is at a standstill.

travisFifty to sixty Spiders were urgently required if GC&CS was to achieve its potential and on the 26th the Deputy Director, Commander Edward Travis wrote:

… we are practically dependent on Bombes for results [and] it appears that we need at least 5 for current Air and Army traffic and 1 spare. This accounts for all 6 now in [sic] order.

Any lingering suggestion that Coventry (or Birmingham for that matter) was “sacrificed” to protect Ultra does not survive examination of the evidence. Ultra gave no unambiguous warning of the date or target of Moonlight Sonata; the city’s defences were nevertheless strengthened but could not prevail against over 400 attackers. Also, a range of counter-offensive measures was set in train in an attempt to degrade the German night bomber force’s effectiveness. On a clear night with the moon near full it is likely that, beams or no beams, Luftwaffe crews would have found Coventry, if not specific targets within it. As was understood at the time, once fires had been started then following waves no longer needed electronic guidance. In fact Air Scientific Intelligence was able to interpret events as proving the success of Radio Counter Measures (RCM):

The policy of KGr. 100 … underwent a complete change from accurate blind bombing to fire-raising consequent upon the defeat of Knickebein. The Coventry raid of 14/15.11.40 was the first result of this new policy … sacrificing its accuracy in order to start large fires.

What this story does demonstrate is that in the late autumn of 1940 the available technologies of night defence had not evolved sufficiently to take a serious toll on the attackers. Radar-directed AA guns, ground-controlled interception, radar-equipped fighters and radio countermeasures would all quickly improve. The harassment of enemy bases by night would by 1944 be a serious impediment to the Luftwaffe. So would the speed and volume of Bletchley’s decrypts and the information that could be derived from them as knowledge of enemy forces, equipment and personnel was built up.

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