page_title: Signals intelligence in modern history
section_title: Cracking the German naval codes
hierarchical_section_title: Signals intelligence in modern history / World War I / Cracking the German naval codes
caption_attribution_description: Office of the admiralty controlling the Royal navy in Whitehall, London. From an engraving by D. Cunego. Building shown (the Ripley Building) is still in existnece but a screen was added in front alongside the road.
context_page_description: SIGINT is a contraction of SIGnals INTelligence. Before the development of radar and other electronics techniques, signals intelligence and communications intelligence were essentially synonymous. Sir Francis Walsingham ran a postal interception bureau with some cryptanalytic capability during the reign of Elizabeth I, but the technology was only slightly less advanced than men with shotguns, during World War I, who jammed pigeon post communications and intercepted the messages carried.
  Flag signals were sometimes intercepted, and efforts to impede them made the occupation of the signaller one of the most dangerous on the battlefield. The middle 19th century rise of the telegraph allowed more scope for interception and spoofing of signals, as shown at Chancellorsville.
  Signals intelligence became far more central to military intelligence generally with the mechanization of armies, development of blitzkrieg tactics, use of submarine and commerce raiders warfare, and the development of practicable radio communications. Even Measurement and Signature Intelligence preceded electronic intelligence, with sound ranging techniques for artillery location.
context_section_description: By the start of the First World War, a worldwide commercial undersea communication cable network had been built up over the previous half-century, allowing nations to transmit information and instructions around the world. Techniques for intercepting these messages through ground returns were developed, so all cables running through hostile territory could in theory be intercepted.
  On the declaration of war, one of Britain's first acts was to cut all German undersea cables. On the night of 3 August 1914, the cable ship Alert located and cut Germany's five trans-Atlantic cables, which ran down the English Channel. Soon after, the six cables running between Britain and Germany were cut. This forced the Germans to use either a telegraph line that connected through the British network and could be tapped, or through radio which the British could then intercept. The destruction of more secure wired communications, to improve the intelligence take, has been a regular practice since then. While one side may be able to jam the other's radio communications, the intelligence value of poorly secured radio may be so high that there is a deliberate decision not to interfere with enemy transmissions.
  Although Britain could now intercept German communications, codes and ciphers were used to hide the meaning of the messages. Neither Britain nor Germany had any established organisations to decode and interpret the messages at the start of the war - the Royal Navy had only one wireless station for intercepting messages, at Stockton-on-Tees.
  However, installations belonging to the Post Office and the Marconi Company, as well as private individuals who had access to radio equipment, began recording messages from Germany. Realizing that the strange signals they were receiving were German naval communications, they brought them to the Admiralty. Rear-Admiral Henry Oliver appointed Sir Alfred Ewing to establish an interception and decryption service. Among its early recruits were Alastair Denniston, Frank Adcock, John Beazley, Francis Birch, Walter Horace Bruford, William Nobby Clarke, Frank Cyril Tiarks and Dilly Knox. In early November 1914 Captain William Hall was appointed as the new Director of the Intelligence division to replace Oliver.
  A similar organisation had begun in the Military Intelligence department of the War Office, which become known as MI1b, and Colonel Macdonagh proposed that the two organisations should work together. Little success was achieved except to organise a system for collecting and filing messages until the French obtained copies of German military ciphers. The two organisations operated in parallel, decoding messages concerning the Western Front. A friend of Ewing's, a barrister by the name of Russell Clarke, plus a friend of his, Colonel Hippisley, approached Ewing to explain that they had been intercepting German messages. Ewing arranged for them to operate from the coastguard station at Hunstanton in Norfolk. They formed the core of the interception service known as 'Y' service, together with the post office and Marconi stations, which grew rapidly to the point it could intercept almost all official German messages.
  In a stroke of luck, the SKM codebook was obtained from the German Light cruiser Magdeburg, which ran aground on the island of Odensholm off the coast of Russian-controlled Estonia. The books were formally handed over to the First Lord, Winston Churchill, on 13 October. The SKM by itself was incomplete as a means of decoding messages since they were normally enciphered as well as coded, and those that could be understood were mostly weather reports. An entry into solving the problem was found from a series of messages transmitted from the German Norddeich transmitter, which were all numbered sequentially and then re-enciphered. The cipher was broken, in fact broken twice as it was changed a few days after it was first solved, and a general procedure for interpreting the messages determined.
  A second important code - the Handelsverkehrsbuch (HVB) codebook used by the German navy - was captured at 
caption: The Admiralty Ripley building. Room 40 succeeded in intercepting and decrypting German naval signals.
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