Before the development of radar and other electronics techniques, signals intelligence (SIGINT) and communications intelligence (COMINT) 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 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 (and to some extent diplomatic) 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 (MASINT) preceded electronic intelligence (ELINT), with sound ranging techniques for artillery location. SIGINT is the analysis of intentional signals for both communications and non-communications (e.g., radar) systems, while MASINT is the analysis of unintentional information, including, but not limited to, the electromagnetic signals that are the main interest in SIGINT.
Origins
Electronic interception appeared as early as 1900, during the Boer Wars. The Royal Navy had installed wireless sets produced by Marconi on board their ships in the late 1890s and some limited wireless signalling was used by the British Army. Some wireless sets were captured by the Boers, and were used to make vital transmissions. Since the British were the only people transmitting at the time, no special interpretation of the signals was necessary.
The Imperial Russian Navy also experimented with wireless communications under the guidance of Alexander Popov, who first installed a wireless set on a grounded battleship in 1900. The birth of signals intelligence in a modern sense dates to the Russo-Japanese War.
As the Russian fleet prepared for conflict with Japan in 1904, the British ship HMS Diana stationed in the Suez canal was able to intercept Russian naval wireless signals being sent out for the mobilization of the fleet, for the first time in history. "An intelligence report on signals intercepted by HMS Diana at Suez shows that the rate of working was extremely slow by British standards, while the Royal Navy interpreters were particularly critical of the poor standard of grammar and spelling among the Russian operators".Report from HMS Diana on Russian Signals intercepted at Suez, 28 January 1904, Naval library, Ministry of Defence, London.
The Japanese also developed a wireless interception capability and succeeded in listening in to the then primitive Russian communications. Their successes emphasized the importance of this new source of military intelligence, and facilities for the exploitation of this information resource were established by all the major powers in the following years.
The Austro-Hungarian Evidenzbureau was able to comprehensively monitor the progress of the Italian army during the Italo-Turkish War of 1911 by monitoring the signals that were sent by a series of relay stations from Tripoli to Rome. In France, Deuxième Bureau of the Military General Staff was tasked with radio interception.
World War I It was over the course of the War that the new method of intelligence collection - signals intelligence - reached maturity. The British in particular built up great expertise in the newly emerging field of signals intelligence and codebreaking.
Failure to properly protect its communications fatally compromised the Russian Army in its advance early in World War I and led to their disastrous defeat by the Germans under Ludendorff and Hindenburg at the Battle of Tannenberg.
France had significant signals intelligence in World War I. Commandant Cartier developed a system of wireless masts, including one on the Eiffel Tower to intercept German communications. The first such station was built as early as 1908, although was destroyed by flooding a few years afterward. In the early stages of the war, French intercepts were invaluable for military planning and provided the crucial intelligence to commander-in-chief Joseph Joffre that enabled him to carry out the successful counterattack against the Germans at the Marne in September 1914.
In 1918, French intercept personnel captured a message written in the new ADFGVX cipher, which was cryptanalyzed by Georges Painvin. This gave the Allies advance warning of the German 1918 Spring Offensive.
US communications monitoring of naval signals started in 1918, but was used first as an aid to naval and merchant navigation. In October 1918, just before the end of the war, the US Navy installed its first DF installation at its station at Bar Harbor, Maine, soon joined by five other Atlantic coast stations, and then a second group of 14 installations. These stations, after the end of World War I, were not used immediately for intelligence. While there were 52 Navy medium wave (MF) DF stations in 1924, most of them had deteriorated.
Cracking the German naval codes
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 the very start of the war from the German-Australian steamer Hobart, seized off Port Philip Heads near Melbourne on 11 August 1914. The code was used particularly by light forces such as patrol boats, and for routine matters such as leaving and entering harbour. The code was used by U-boats, but with a more complex key. A third codebook was recovered following the sinking of German destroyer SMS S119 in a battle off Texel island. It contained a copy of the Verkehrsbuch (VB) codebook, intended for use in cables sent overseas to warships and naval attachés, embassies and consulates. Its greatest importance during the war was that it allowed access to communications between naval attachés in Berlin, Madrid, Washington, Buenos Aires, Peking, and Constantinople.
The German fleet was in the habit each day of wirelessing the exact position of each ship and giving regular position reports when at sea. It was possible to build up a precise picture of the normal operation of the High Seas Fleet, indeed to infer from the routes they chose where defensive minefields had been place and where it was safe for ships to operate. Whenever a change to the normal pattern was seen, it immediately signalled that some operation was about to take place and a warning could be given. Detailed information about submarine movements was also available.
Direction finding
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.