The Luftwaffe traffic being deciphered by the British in 1940 was growing in volume but patchy nevertheless. Large numbers of messages would be picked up from some units and HQs, little or nothing from others. I’ve only recently started looking at the relevant files, prompted partly by my annoyance at some of the TV programmes made for the 70th Anniversary of the Battle of Britain.

You don’t have to read the messages for long to realise that some themes crop up repeatedly and my idea is eventually to post a series of articles here on those topics. I don’t imagine that this source is going to necessitate a rewrite the history of the Battle of Britain all on its own but it does seem to offer some additional details and insights, some of whose significance would probably only be apparent to researchers who (unlike me) have specialised in the campaign.

You get the sense that in 1940 the analysts were still learning about the Luftwaffe’s functioning with each day that passed whereas towards the end of the war they seem very much to have a confident understanding of the organisation they were dealing with and many of its personnel, even if it still could produce unwelcome surprises.

The individual files for 1940 are big: HW5/4 spans the period 4 August – 11 September and has almost 500 pages. The messages are not reported in the same way as they would be in later HW5 series files. Each set of messages carries a CX/JQ/ serial number at the top and then a sequence of numbered paragraphs. Each of these paragraphs appears to represent a single deciphered message but usually heavily paraphrased and often embodying commentary by the British analysts, who sometimes essay humorous remarks about their enemies’ foibles.

In the margins by some of these items you may find “T1”, “T2” etc. to denote material for which a teleprint has been issued but the teleprints themselves are not on the file.

Paragraphs are grouped under topic headings such as operations, Flak, aerodromes, aircraft markings, signals, administration and personnel. The great majority of the items are from the Luftwaffe.

The individual items all maintain the fiction that a human “source” has been eavesdropping on German officers’ conversations or searching their desks. It’s not made clear if all times are normalised to GMT until CX/JQ/306 of 14 September 1940 (at least this is the first instance I've noticed so far). I haven’t yet worked out the pattern (if any) on which CX/JQ/1 gave way to CX/JQ/2 and so on. Sometimes there is one CX/JQ a day, at other times two and there’s no set number of sections in each one.

A few days before this part of the site went live, the man who made it possible died. John Herivel's inspired idea that German operators would not be altogether conscientious in changing their Enigma machines' settings each day gave the British consistent access to Luftwaffe signals in the summer of 1940.