World War I cryptography
Open-knowledge reference entry
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
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
William Montgomery (cryptographer) Room 40
MI1 British Military (Army) Intelligence
Malcolm Vivian Hay, MI1(b), head from 1915
Oliver Strachey MI1
Playfair cipher
Russia
In the 1914 Battle of Tannenberg, different corps of the Russian Imperial army were unable to decipher each other's 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.
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