World War I cryptography
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 Malcolm Vivian Hay, MI1(b), head from 1915 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