Preparing the Ground for Room 40

There was nothing recognisable as Sigint in the UK before the First World War started, but we know a fair amount about interception before the war started and can make reasonable assumptions about why there was no permanent organisation created to monitor the wireless traffic of foreign armed forces. The idea that there was no serious thinking about the value of interception, and, its corollary, that there was no thinking about how an enemy might exploit UK communications, is not tenable. What follows is about the Admiralty – I’ll perhaps look at the War Office in another post.

The earliest indication I have seen so far of somebody thinking about a potential downside to the wireless telegraphy (WT) systems first being trialled by RN ships at the start of the last century comes from a 1900 report. Between March and May 1900 four ships on the Cape of Good Hope Station, HMS Forte, HMS Magicienne, HMS Raccoon and HMS Thetis, were equipped with Marconi WT equipment and carried out trials. Their reports, forwarded to the Admiralty by the Senior Naval Officer on the Delagoa Bay and Natal Division, concentrated on the performance of the equipment and its potential, but the report from the Captain of HMS Raccoon added:

‘I am strongly in favour of its suitability for communications between Her Majesty’s ships especially during patrolling operations of a similar character as those existing here. Had the presence of an enemy’s fleet to be considered, it would be a question if the possession of this instrument would not tend to disclose the proximity of your presence to the enemy.’

At its most basic, those thinking about foreign communication usage thought at the message level, rather than at the carrier level, and saw any potential value as deriving from messages transmitted during actions. Thus, in the 1902 Royal Navy fleet exercises, the Admiralty issued an instruction forbidding either fleet from acting on information derived from intercepted messages alone, because ‘in a real action, the signals would probably be unintelligible to the other side’; and in 1904, the British squadron in Chinese waters intercepted messages being passed between a Russian Admiral and his staff. The RN Commander reported to the Admiralty that ‘the character of the messages was not important, but the fact of interception showed possibilities that a belligerent's messages could be and probably would be intercepted’.

Radio procedures of foreign navies (French, German, Japanese, American and Italian) were studied to provide recognition: in 1904 British warships were instructed to transmit to the Admiralty copies of all foreign radio messages which they intercepted and in 1904 and 1905 the NID was informed of Intercept of Russian naval traffic by ships at Suez, the intercept of German naval traffic by ships at Corfu; and of Dutch stations by ships in the Baltic. Furthermore, the RN had acquired the French Naval Wireless Telegraphy Handbook of 1904; and by 1906, procedures used by the American and Japanese Navies had been added to the list.

The accepted view was that though wireless messages might be intercepted, encryption would render any intercepted message unreadable. In 1906 the commander of the Home Fleet (and later First Sea Lord) Arthur Wilson, stated that even if ‘the enemy has our signal books’, all messages in this compromised codebook would remain entirely secret so long as they were superenciphered by means of an elementary transposition cipher. In 1907 the head of the navy’s radio service and the Director of Naval Intelligence (DNI) both doubted that encoded radio traffic could ever be broken, since ‘under most circumstances it will only be necessary to cypher a few words in each message to render it quite unintelligible’.

The belief that encryption would render any message unreadable led to thinking in another direction: how to deny an enemy the possibility of wireless communication. Again, this thinking was not developed: jamming was not a possibility because it would mean jamming of own comms as well as of the enemy's. There was little thinking beyond the destruction from the sea of enemy coastal wireless stations and the cutting of enemy telegraphic cables.

Counter-jamming was studied: already by 1909 the first experiments in directional wireless telegraphy were being carried out by the Admiralty, at both shore stations and in ships at sea.

There had been no cryptanalytic organisation in the UK since 1844 but crucially, the pre-1844 Secret Offices looked only at civil and diplomatic material, not military. The Indian Army, following its experiences in South Africa, had set up a two man cryptanalytic bureau in India, but its function was to look at diplomatic and attaché traffic acquired from telegraph companies, something that, while legal in India, was illegal in the UK, and the product of which was of no interest to the British government.

In 1908 Fleet Paymaster Charles Rotter of the Naval Intelligence Division asked that any German Naval messages intercepted should be logged and forwarded to the NID. This work had certainly begun by 1909 and a file of this material certainly existed in 1973 in GCHQ though it was probably subsequently returned to the MOD and is now waiting to be discovered in an ADM piece in The National Archives.

The file contained raw traffic and work-sheets. Some of the raw traffic was recorded on specially printed forms headed ‘Return of Intercepted Wireless Telegraph Messages for the month of ...’ These returns were prepared at the point of interception, presumably by transcription from the actual logs, and sent to ‘Admiral Commanding Reserves’ by the ‘Chief Officer’.

The worksheets showed successful decryption of one encryption system, and work on callsigns and the collation of versions received from the different interception points. These interception points were: Whitehall (presumably the Admiralty), Aberdeen, Ipswich, Dover, Rosyth, Port Patrick, Pembroke Dock, St. Helier, Essex Hill, Hunstanton, and, at least from 1912, Scarborough. At the Admiralty end, monthly batches of returns as received from the stations were ‘referred for information’ to DID in person. What the latter made of the raw intercepts is not clear.

Callsigns were two-, three-, or four-letter. It was easy to identify many: for example RO, NA, AKO and AHO stood respectively for the ships ROON, NAUEN, KOENIGSBERG and HOHENZOLLERN. Frequencies were reported as ‘Wavelengths in feet’. They included 5000, 6000 and 6500 (the roundness of the figures suggests strongly that the measurements were pretty rough).

The monthly return forms had a column for ‘Remarks, Strength of Signals; If musical, etc.’ It was not much used, but some transmissions were described as ‘musical’ or ‘high musical’; others were described as ‘whistling note’ and ‘quenched spark’. Strengths were given in a scale up to 10 and ‘rates’ – presumably words-per-minute – were of the order of 12 to 15.

The traffic that was read at the time was a 10-letter code; each group consisted of two more or less pronounceable 5-letter ‘words’. There were clear indications that a German codebook had been acquired physically by some means, rather than that it had been reconstructed cryptanalytically. All the messages were originated by ‘Admiralstab’, callsign KMD (probably Kriegsmarinedienststelle – Naval HQ), using the main German naval transmitter at Norddeich. The messages refer to movements of German ships or to the deployment of British and other warships in the Mediterranean and home waters – and on one occasion to an eruption of Mount Etna! The readable sequence started in March 1910 and finished with the following message dated 11 July 1910: ‘This is the last telegram from the Admiralstab’. (Or might this have been a comment?)

There is no evidence that any other cypher was read at the time. Most of the unread traffic is in 5-letter transposition systems.

Conventional wisdom is that the Naval Intelligence Division had arranged for the Secret Service to purchase a copy of a German Naval codebook from an agent. £600 went into this venture but the codebook which eventually turned up was a forgery. I wonder, however, whether it isn’t just as likely that the codebook was used until 11 July 1910 at which point it was superseded.

Though this activity by Rotter was tolerated, he was acting in isolation. At his request, during the naval manoeuvres of 1912 and 1913 a separate division of the Admiralty War Room, known as Section C, had been assigned to work on intercepted wireless traffic, but nevertheless when the War Room was mobilised on 30 July 1914 it was simply decided that such a unit was unnecessary, and Section C was dropped.

Just before the advent of war, Cdr Frederick Loring RN, probably the Navy's expert in wireless telegraphy at the time, summed up why interception would not prove a serious threat to naval wireless in wartime.

‘... the more skilled the organisation, the more difficult it is for a strange operator to take down with the necessary accuracy the groups of a code message: he cannot ask for the repetition of doubtful groups, and he has no intimate and daily familiarity with the methods of his opponent to assist him in his task. And, after all, giving the enemy every advantage, giving him a perfect record of the signals, the key of the code to his hand and equal facility of skill and language to translate it for use—a most improbable combination, it must be admitted—he has still failed to prevent the all-important information reaching its destination.’

That Loring was wrong in 1914, just as the FSL and the DNI had been wrong in 1906 and 1907, shows how different Sigint is from any other sort of intelligence that existed in 1914 and how difficult it was to imagine it. A combination of the traffic analysis carried out in the War Office by Room 40 staff in September and October 1914, the capture of the Magdeburg Codebook and its arrival in London at the end of October, Rotter’s working out the superencryption system used by the German High Seas Fleet, and Winston Churchill’s imaginative insight into this totally new source meant that by 8 November Room 40 had been established as the first cryptanalytic bureau in the UK since 1844 and was ready to become the UK’s first Sigint organisation.