Codebreaking
During World War I, Knox was recruited to the Royal Navy's cryptological effort in Room 40 of the Admiralty Old Building, where among other tasks he was involved in breaking the Zimmermann Telegram which brought the USA into the war.
Between the two World Wars Knox worked on the great commentary on Herodas that had been started by Headlam, damaging his eyesight while studying the British Museum's collection of papyrus fragments, but finally managing to decipher the text of the Herodas papyri. The Knox-Headlam edition of Herodas finally appeared in 1922. He married in 1920, forgetting to invite his brothers to his wedding.
During World War I he had been elected Librarian at King's College, but never took up the appointment. After the war Knox intended to resume his researches at King’s, but he was persuaded by his wife to remain at his secret work; indeed, so secret was this work that his own children had no idea, until many years after his death, what he did for a living, and his contribution to the war effort.
In 1937 he cracked the code of the commercial Enigma machines used by Franco's Nationalists in the Spanish Civil War, but knowledge of this breakthrough was not passed on to the Republicans.
Knox was one of the British participants in the Polish-French-British conference held on July 25, 1939, at the Polish Cipher Bureau facility at Pyry, south of Warsaw, Poland, in which the Poles disclosed to their French and British allies their achievements in Enigma decryption. Knox was chagrined — but grateful — to learn how simple was the solution of the Enigma's entry ring (standard alphabetical order). After the meeting, he sent the Polish cryptologists a very gracious note in Polish, on official British government stationery, thanking them for their assistance, and enclosing a beautiful scarf featuring a picture of a Derby race, and a set of paper 'batons' that he had presumably used in his attempts to break the German Enigma.
To break non-steckered Enigma machines (those without a plugboard), Knox used a system known as 'rodding', a linguistic as opposed to mathematical way of breaking codes. This technique worked on the Enigma used by the Italian Navy and the German Abwehr. Knox worked in 'the Cottage', next door to the Bletchley Park mansion, as head of a research section, which contributed significantly to cryptanalysis of the Enigma.
Knox's work was cut short when he fell ill with lymph cancer. When he became unable to travel to Bletchley Park, he continued his cryptographic work from his home in Hughenden, Buckinghamshire, where he received the CMG. He died on 27 February 1943. A biography of Knox, written by Mavis Batey, one of 'Dilly's girls', the female codebreakers who worked with him, was published in September 2009.
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