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Alfred Dillwyn 'Dilly' Knox (23 July 1884 – 27 February 1943) was a classics scholar at King's College, Cambridge, and a British codebreaker. He was a member of the World War I Room 40 codebreaking unit, and later at Bletchley Park he worked on the cryptanalysis of Enigma ciphers until his death in 1943.


Family and education

Dillwyn Knox, the fourth of six children[1], was the son of Edmund Arbuthnott Knox, and the brother of Ronald Knox, E. V. Knox and Wilfred. L. Knox[1]. He was father of Oliver Arbuthnot Knox.

Dillwyn, known as "Dilly," Knox was educated at Summer Fields School, Oxford, and then Eton College[1]. He studied classics at King's College, Cambridge, and was elected a fellow in 1909[1].


Knox was recruited to the Royal Navy's codebreaking effort in Room 40 of the Admiralty Old Building during World War I.[2]

In 1937 Knox 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.[3]

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 was applied successfully against the Enigma used by the Italian Navy and the German Abwehr[4]. 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.[5] 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[6]. He died on 27 February 1943.[6] 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.[7]


  1. ^ a b c d Batey, Mavis (2004). Knox, (Alfred) Dillwyn (1884–1943). Oxford Dictionary of National Biography.  
  2. ^ Goebel, Greg. "Codes, Ciphers, & Codebreaking". [4.1] Room 40 & the Zimmermann telegram / German codebreakers. Retrieved 2009-11-02.  
  3. ^ Graham Keeley. Nazi Enigma machines helped General Franco in Spanish Civil War The Times 24 October 2008. p 47. States "Professor Denis Smyth, of the University of Toronto, an expert on Second World War intelligence operations, said that the British code breaker Alfred Dilwyn Knox cracked the code of Franco's machine in 1937, but 'this information was not passed on to the Republicans'."
  4. ^ Carter, Frank, Rodding,, retrieved 2009-01-20  
  5. ^ Sebag-Montefiore (2000) p. 350
  6. ^ a b Fitzgerald (1977) p. 249-250
  7. ^ Batey (2009)


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