With the rise of easily-intercepted wireless telegraphy, codes and ciphers were used extensively in World War I. The decoding by British Naval intelligence of the Zimmermann 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. The most commonly used codes were simple substitution 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. Britain British decrypting was carried out in Room 40 by the Royal Navy and in MI1 by British Military (Army) Intelligence. Zimmermann telegram Arthur Zimmermann MI1 British Military (Army) Intelligence Room 40 Royal Navy (Britain) Alastair Denniston Room 40 James Alfred Ewing Room 40, first head Nigel de Grey Room 40 William R. Hall ‘Blinker’ Hall, Room 40, second head Dilly Knox Room 40 Oliver Strachey MI1 William Montgomery (cryptographer) Room 40 Playfair cipher Russia In the 1914 Battle of Tannenberg, different corps of the Russian Imperial army were unable to decipher each others messages, so they sent them in plain text. They were easily intercepted. Meanwhile, German cryptanalysts were also able to read the enciphered ones. Ernst Fetterlein was in the Tsarist Russian Ministry of Foreign Affairs from 1896 and solved (among others) German, Austrian and British codes. He became chief cryptographer with the rank of admiral. With the Russian Revolution in 1917 he fled to Britain and was recruited to Room 40 in June 1918 to work on Austrian, Bolshevik and Georgian codes. The Russians used an overcomplicated version of the Vigenère Cipher. It was broken within three days by Austro-Hungarian cryptanalyst Hermann Pokorny. France The French Army employed Georges Painvin, and Étienne 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 to Colonel Cartier of the War Ministry, France intercepted over 100,000,000 words from German radiograms during the course of the war. The Tableau de Concordance