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Histories and memoirs have spoken of Churchill reviewing that day’s Ultra briefing but the only relevant items in the CX/JQ report issued at 02.40 next day were:

(1) a minor correction to a message about a previous day’s navigational beam setting;

(2) a commentary on Y-Service information about Moonlight Sonata whose only new point was that the D3R tuning signal had been intercepted at 13.00 GMT that day. (Overall reliability of this teleprint was rated as “(B)”); and

(3) the advice that “Source has some reason to believe that transmission on to-night’s target may start at 1700 (GMT), 14/11. No details of target yet available.” (Reliability of this teleprint was only “(C)”, the next-to-lowest level).

The file does not reveal the times at which these individual items were teleprinted from Bletchley but the second one must have come after the Air Staff’s paper was compiled since that only said that watch would be kept for the tuning signal, not that it had been sent.

By 15.00 BST it had been established that the “river” beams were intersecting over Coventry and at 16.15 hours the order was given to Fighter, Bomber and Coastal Commands and to No. 80 Wing to execute Cold Water. An hour later, the Air Ministry approved this last formation’s detailed proposals for an attack on the Cherbourg transmitters.

In 1940 Peter Gray Lucas of the Air Ministry was working at the Cheadle Y-Service Station, on low-grade Luftwaffe tactical signals. In 1993 he wrote that:

A harbour defence command in Antwerp regularly received notice of ‘own’ aircraft about to fly over. On the afternoon of 14 November 1940 the signal read ‘ANGRIFF [attack] KORN’, but the [human] computors could not guess at the time and did not guess until later that KORN was the code-word for Coventry.

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