This article was prompted by a post on Neil Page’s (highly recommended) FalkeEins blog. Reviewing a recent book on the Battle of Britain, he remarked that it said nothing about ULTRA intelligence and its role in the campaign. Having already written something about ULTRA and Adlertag, I decided to look next at the period leading up to it.

Although the Battle of Britain continues to be written about 80 years after the events, the part played by ULTRA intelligence has received little detailed attention. It was never the sole source of intelligence on German dispositions and intentions: shot-down aircraft were examined, prisoners were interrogated, information passed through neutral embassies, aerial photos were taken, wireless traffic was plotted, useful knowledge was derived from newspapers and broadcasts. All of these methods contributed to the overall picture.

ULTRA had value and limitations and I would argue that both are best appreciated by studying the messages themselves. If Allied foreknowledge of German intentions was exaggerated when the secret was disclosed in the 1970s, then subsequent overviews have sometimes downplayed what ULTRA could in fact offer. In 1990, three aviation historians, Hans Ring, Winfried Bock and Heinrich Weiß, wrote an article for Flugzeug magazine attempting to dispel what they saw as the myths of the Battle of Britain, ULTRA included (my translation):

For the “Battle” it can be said that the British did not find out German operational orders, indications of the targets, times and strengths of attacks from “Ultra”. Mainly [they obtained] administrative and organisational information … without influence on actual combat operations.

What can have led them to such a confident assertion? Assuredly it was not reading the actual 1940 decrypts since these would not be released to the UK Public Record Office for another six years. Instead it seems likely that they relied, directly or indirectly, on the four-volume official history, British Intelligence in the Second World War (F. H. Hinsley et al, 1979–90). In 2015 Max Hastings (The Secret War) could still write that early in the conflict “Ultra could do little to assist the RAF’s ongoing struggle with the Luftwaffe for mastery of the skies”; he cites no file references for individual decrypts but includes Hinsley in his bibliography.

Stephen Bungay (The Most Dangerous Enemy, 2000) briefly discusses “a device called ‘Ultra’, noting that Air Chief Marshal Dowding was not on the circulation list for decrypts until the Battle was winding down. He does however say (citing Sebastian Cox of the RAF’s Air Historical Branch) that “some information gleaned from Ultra, such as the plan for Luftflotte V to attack northern England on 15 August was probably passed to him”. This would be consistent with a letter of 7 November 1940 from Air Commodore Archibald Boyle of RAF Intelligence to the Chief of the Secret Intelligence Service: “… if and when we get information of value, we must use it”. However, if there are messages warning of Luftflotte 5’s attack then I have not recognised them as such.

Reading about ULTRA is one thing, reading it is quite another.

Deciphered signals rarely revealed the plans for a major air operation before it happened but offered clues which, taken along with other current and earlier traffic, enabled analysts to draw conclusions about the state of enemy forces, their capabilities, intentions and operational patterns (e.g. routine reconnaissances). In the summer of 1940 Bletchley Park had yet to build up the extensive card indexes that later in the war would allow it to make the most out of messages that on their own might seem inconsequential. Then they were encountering names, places and formations for the first time. The year had brought two major breaks into machine-ciphers: from the Norwegian campaign in early April and from the campaign in France in the third week of May. Since, except in rare cases, we do not have the individual decrypts, we do not know at what time each was issued. The only pinpoints we have are the times and dates of the compilations—sometimes three per day—of paraphrased information. From these it seems that traffic was generally being broken within about 24 hours of transmission but we cannot be more precise.

We do however have a description of the Air Ministry’s procedures for handling and distributing this special intelligence. The material came direct from the Secret Intelligence Service (M.I.6) by teleprinter and was handled by a staff of specially selected officers who were always on duty. A message of operational value went to the Duty Group Captain, “to take the necessary operational action through the operational director, or, if necessary, direct to to commands”. These items and ones which did not demand “immediate operational action but [did] require analysis” went to various sub-sections of the German Section to “extract … all information of value”, such as orders of battle, locations and commanders’ names. The Section would only ask for the German-language original in exceptional cases, where part of the translation was in doubt.

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