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With the rise of easily interceptedwireless telegraphy, codes and ciphers were used extensively inWorld War I. The decoding byBritish Naval intelligence of theZimmermann telegram helped bring the United States into the war.
Trench codes were used by field armies of most of the combatants (Americans, British, French, German) in World War I.[1]
The most commonly used codes were simplesubstitution ciphers. More important messages generally used mathematical encryption for extra security. The use of these codes required the distribution of codebooks to military personnel, which proved to be a security liability since these books could be stolen by enemy forces.[2]
British decrypting was carried out inRoom 40 by the Royal Navy and inMI1 by British Military (Army) Intelligence.
The French Army employedGeorges Painvin, andÉtienne Bazeries who came out of retirement, on German ciphers. Due to their prewar activities, the French were more prepared than any other nation involved in the war to decode German radiograms. At the beginning of the war, France had eight intercept stations: Maubeuge, Verdun, Toul, Epinal, Belfort, Lille, Rheims, and Besançon. During the war, they set up many more stations, including one in the Eiffel Tower. According toColonel Cartier of the War Ministry, France intercepted over 100,000,000 words from German radiograms during the course of the war.[4]
TheImperial German Army and theAustro-Hungarian Army intercepted Russian radio communications traffic, although German success at theBattle of Tannenberg (1914) was due to interception of messages between theImperial Russian Army commanders in cleartext.
The GermanAbhorchdienst, a code-breaking bureau composed mainly of mathematicians, was established in 1916.
The Germans had specific regulations regarding which kinds of codes and ciphers could be used under given circumstances. Within three kilometers of the front lines, known as the danger zone, all communications were required to be in a code known as the three-number code. This was the only code or cipher permitted. Behind this danger zone, another code known as the three-letter code was allowed to be used. Communications between divisions, corps, and army headquarters were done with the ADFGVX cipher.[5]
The ADFGX andADFGVX field ciphers were a modifiedpolybius system with single order double columnar transposition and frequent key change, with letters optimized for Morse. It was later broken by the famous French cryptanalystGeorges Painvin. The breaking of the ADFGX cipher by Painvin was the second time during the war that cryptanalysis played a major role in shaping events (the first being the interception and cracking of the Zimmerman Telegram). By breaking the cipher, the French were able to decode an intercepted message about the forwarding of munitions for a German offensive, letting the French know where and when the offensive would occur, and thus allowing them to stop it. This message became known as "The Radiogram of Victory."[6]
Herbert Yardley began as a code clerk in the State Department. After the outbreak of war he became the head of the cryptographic section of Military Intelligence Section(MI-8)[7] and was with the American Expeditionary Force in World War I as a Signals Corps cryptologic officer in France. He later headed the Cipher Bureau, a new cryptanalysis group started in 1919, immediately after World War I, and funded jointly by the State Department and the US Army.
Some American cryptography in World War I was done at theRiverbank Laboratories, Chicago, which was privately owned by Colonel George Fabyan.Elizebeth Friedman,William F. Friedman andAgnes Meyer Driscoll worked there.
The US Navy used the cryptographic codeA-1. The US Navy cryptanalysis group,OP-20-G, was also started after World War I (in 1922).
The US also started employing Indiancode talkers in World War I, initially with members of the Cherokee and Choctaw tribes.
