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Alfred Dillwyn Knox

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Alfred Dillwyn Knox

Alfred Dillwyn "Dilly" Knox
Born Alfred Dillwyn Knox
(1884-07-23)23 July 1884
Died 27 February 1943(1943-02-27) (aged 58)
Cause of death Lymph cancer
Nationality English
Other names Dilly
Citizenship British
Education Template:Plainlist
Alma mater King's College, Cambridge
Occupation Template:Plainlist
Employer Template:Plainlist
Title Template:Plainlist
Children Template:Plainlist
Parents Edmund Arbuthnott Knox
Relatives Template:Plainlist

Alfred Dillwyn "Dilly" Knox, CMG (23 July 1884 – 27 February 1943) was a British classics scholar and papyrologist at King's College, Cambridge and a codebreaker. As a member of the World War I Room 40 codebreaking unit, he helped decrypt the Zimmermann Telegram which brought the USA into the war.[1] He joined the GC&CS at the war's end.[2] As Chief Cryptographer,[2] Knox played an important role in the Polish-French-British meetings on the eve of World War II which disclosed Polish cryptanalysis of the Axis Enigma to the Allies.[3] At Bletchley Park he worked on the cryptanalysis of Enigma ciphers until his death in 1943. He built the team and discovered the method that broke the Italian Naval Enigma, producing the intelligence credited with Allied victory at the Battle of Cape Matapan. In 1941, Knox broke the Abwehr Enigma.[4] By the end of the war, Intelligence Service Knox had disseminated 140,800 Abwehr decrypts,[4] including intelligence important for D-Day.[5]

Personal life and family

Dillwyn Knox, the fourth of six children,[6] was the son of Edmund Arbuthnott Knox, tutor at Merton College and later Bishop of Manchester; he was the brother of E. V. Knox, Wilfred Knox and Ronald Knox,[6] and uncle of the novelist Penelope Fitzgerald.[7]

Dillwyn—known as "Dilly"—Knox was educated at Summer Fields School, Oxford, and then Eton College.[6] He studied classics at King's College, Cambridge from 1903,[8] and in 1909 was elected a Fellow[6] following the death of Walter George Headlam, from whom he inherited extensive research into the works of Herodas. While an undergraduate he was friends with Lytton Strachey and John Maynard Keynes. Knox privately coached Harold Macmillan, the future Prime Minister at King's for a few weeks in 1910, but Macmillan found him "austere and uncongenial".[8]

He married in 1920, forgetting to invite two of his three brothers to his wedding.[9] He was the father of Oliver Arbuthnot Knox and Christopher Maynard Knox.

Academic scholarship

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.[10]


World War I

The sailor in Room 53

has never, its true, been to sea

but though not in a boat

he has served afloat —

in a bath in the Admiralty.

— Alice in ID25 by Frank Birch[11]

Soon after World War I broke out in 1914,[2] Knox was recruited to the Royal Navy's cryptological effort in Room 40 of the Admiralty Old Building,[12] where some of his best work is said to have done in the bath (in Room 53).[11] In 1917, Knox followed Room 40 with its expansion into ID25.[2]

Among other tasks, he was involved in breaking:

  • the Zimmermann Telegram which brought the USA into the war.[1]
  • much of the German admiral's flag code by exploiting an operator's love of romantic poetry.[2]

Between the wars

Government code and cypher school

Oh, if a time should ever come when we're demobilized

How we shall miss the interests which once life comprised!

— Dilly the Dodo[2], Alice in ID25 by Frank Birch

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.[8]

Commercial Enigma

The Enigma machine became available commercially in the 1920s. In Vienna in 1925,[13] Dilly bought the Enigma 'C' machine evaluated by Hugh Foss in 1927 on behalf of GC&CS. Foss found "a high degree of security" but wrote a secret paper describing how to attack the machine if cribs — short sections of plain text — could be guessed.[3] When — a decade later — Knox picked up this work, he developed a more effective algebraic system (rodding) based on the principles described by Foss.[13]

Spanish Enigma

Germany Navy adopted Enigma in 1926, adding a plug-board ('stecker') to improve security. Nazi Germany supplied non-steckered machines to Franco's Nationalists in the Spanish Civil War.[3] On April 4, 1937, Knox broken Franco's Enigma[3] but knowledge of this breakthrough was not shared with the Republicans.[14] Soon afterwards, Dilly began to attack signals between Spain and Germany encrypted using steckered Enigma machines.[3]

On the eve of war

GC&CS began to discuss Enigma with France's Deuxième Bureau in 1938, obtaining from the Bureau details of Wehrmacht Engima supplied by Asché and signal intercepts, some of which must have been made in Eastern Europe. This led the French to disclose their links with Polish cryptographers.[3]

As GS&CS chief cryptographer[2] Dilly, together with Hugh Foss and Alastair Denniston, represented GC&CS at the first Polish-French-British meeting at Paris in January 1939. The Poles were ordered to disclose nothing of importance at this time, and the British codebreakers left disappointed. Dilly described his system of rodding, and he left the Polish codebreakers sufficiently impressed for his presence to be requested at a second meeting.[3]

Knox grasped everything very quickly, almost quick as lightning. It was evident that the British had been really working on Enigma ... So they didn't require explanations. They were specialists of a different kind, of a different class.

Marian Rejewski[2]

Knox attended the second Polish-French-British conference which was held on 25–26 July 1939 at the Polish Cipher Bureau facility (at Pyry, south of Warsaw, Poland). Here, the Poles began to disclose to their French and British allies their achievements in solving Enigma decryption.[15]

Though Marian Rejewski, the Polish cryptographer and mathematician who solved the plugboard-equipped Enigma used by Nazi Germany, approached the problem through permutation theory (whereas Knox applied linguistics) a good personal relationship was quickly established at the conference. The good impression made by Rejewski on Knox played an important role in increasing recruitment of mathematicians to Bletchley Park.[2]

Knox was chagrined — but grateful — to learn how simple was the solution of the Enigma's entry ring (standard alphabetical order).[15]

It was such an obvious thing to do, really a silly thing to do, that nobody, not Dilly Knox or Tony Kendrick or Alan Turing, ever thought it worthwhile trying it.

Peter Twinn[3]

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 sending “sincere thanks for your cooperation and patience”.[2] Enclosed were a beautiful scarf featuring a picture of a Derby winner and a set of paper 'batons'.[15]

I don't know how Knox's method was supposed to work, most likely he had hoped to vanquish Enigma with the batons. Unfortunately we beat him to it.

Marian Rejewski[2]

These 'batons' were known as rods to the British and had been used to solve the Spanish Enigma. Knox's rodding method was later used to break the Italian Naval Enigma.[2]

World War II

Knox's rodding method

To break non-steckered Enigma machines (those without a plugboard), Knox (building on earlier research by Hugh Foss[3]) developed 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[16] 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.[6]

Knox's team at The Cottage used rodding to decrypt intercepted Italian naval signals describing the sailing of an Italian battle fleet, leading to The Battle of Cape Matapan. Admiral John Godfrey, Director of Naval Intelligence credited the Allied victory at Matapan to this intelligence.[2]

Intelligence Services Knox

In October 1941, Dilly solved the Abwehr Enigma.[4] Intelligence Services Knox (ISK) was established to decrypt Abwehr communications.[4] In early 1942, with Knox seriously ill, Peter Twinn took change of running ISK[5] and was appointed head after Knox's death.[4] By the end of the war, ISK had decrypted and disseminated 140,800 messages.[4]

Intelligence gained from these Abwehr decrypts played an important part in ensuring the success of Double-Cross operations by MI5 and M16, and in Operation Fortitude, the Allied campaign to deceive the Germans about D-Day.[5]


Knox's work was cut short when he fell ill with lymph cancer.[17] 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.[18] He died on 27 February 1943.[18] 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.[19]

Classified poetry

These have knelled your fall and ruin, but your ears were far away

English lassies rustling papers through the sodden Bletchley day.

—Dilly Knox, Epitaph on Matapan to Mussolini[2]

Knox celebrated the victory at Battle of Cape Matapan with poetry, which remained classified until 1978.[2]


In fiction

Knox is shown recruiting Alan Turing to Bletchley Park in Hugh Whitemore's play, Breaking the Code (1986). In the 1996 television film, he is portrayed by Richard Johnson.



  • (Updated and extended version of Action This Day: From Breaking of the Enigma Code to the Birth of the Modern Computer Bantam Press 2001)
  • (Updated and extended version of Action This Day: From Breaking of the Enigma Code to the Birth of the Modern Computer Bantam Press 2001)
  • (Updated and extended version of Action This Day: From Breaking of the Enigma Code to the Birth of the Modern Computer Bantam Press 2001)

External links

  • Knox in the history of Bletchley Park
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