page_title: Signals intelligence in modern history
section_title: Direction finding
hierarchical_section_title: Signals intelligence in modern history / World War I / Direction finding
caption_attribution_description: Henry Joseph Round
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: The use of radio receiving equipment to pinpoint the location of the transmitter was also developed during the war. 
  Captain H.J. Round working for Marconi, began carrying out experiments with direction finding radio equipment for the army in France in 1915. Hall instructed him to build a direction finding system for the navy. This was sited at Lowestoft and other stations were built at Lerwick, Aberdeen, York, Flamborough Head and Birchington and by May 1915 the Admiralty was able to track German submarines crossing the North Sea. Some of these stations also acted as 'Y' stations to collect German messages, but a new section was created within Room 40 to plot the positions of ships from the directional reports.
  Room 40 had very accurate information on the positions of German ships, but the Admiralty priority remained to keep the existence of this knowledge secret. From June 1915 the regular intelligence reports of ship positions ceased to be passed to all flag officers, but only to Admiral Jellicoe himself. Similarly, he was the only person to receive accurate charts of German minefields prepared from Room 40 information. No attempts were made by the German fleet to restrict its use of wireless until 1917, and then only in response to perceived British use of direction finding, not because it believed messages were being decoded.
  It became increasingly clear, that as important as the decrypts were, it was of equal importance to accurately analyse the information provided. An illustration of this was provided by someone at the Admiralty who knew a little too much detail about SIGINT without fully understanding it. He asked the analysts where call sign "DK" was located, which was that used by the German commander when in harbour. The analysts answered his question precisely, telling him that it was "in the Jade River".  Unfortunately the High Seas Fleet commander used a different identifier when at sea, going so far as to transfer the same wireless operator ashore so the messages from the harbour would sound the same.  The misinformation was passed to Jellicoe commanding the British fleet, who acted accordingly and proceeded at a slower speed to preserve fuel. The battle of Jutland was eventually fought but its lateness in the day allowed the enemy to escape.
  Jellicoe's faith in cryptographic intelligence was also shaken by a decrypted report that placed the German cruiser SMS Regensburg near him, during the Battle of Jutland. It turned out that the navigator on the Ravensburg was off by 10 miles (16 km) in his position calculation. During Jutland, there was limited use of direction finding on fleet vessels, but most information came from shore stations. A whole string of messages were intercepted during the night indicating with high reliability how the German fleet intended to make good its escape, but the brief summary which was passed to Jellicoe failed to convince him of its accuracy in light of the other failures during the day.
caption: Captain H.J. Round devised and oversaw the construction of an array of direction finding stations that were able to track the movements of enemy ships.
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