Meteorologist, oceanographer, Python solvem probler, experimenter, Raspberry Pi tinkerer, geek dad, manager, space enthusiast, ham radio lover, science columnist, ADHDer, synthetic intellect curious, linux admin cosplayer.

Alfred Dillwyn “Dilly” Knox – Research Notes

Basic Facts

Full name: Alfred Dillwyn Knox, CMG Known as: Dilly Knox Born: 23 July 1884 Died: 27 February 1943 Nationality: British Education: King’s College, Cambridge (classics and papyrology) Role: Chief cryptanalyst, Government Code and Cypher School (GC&CS)

Early Life and Academic Career

Knox came from a distinguished intellectual family – his father was the Bishop of Manchester; his brothers included the satirist E.V. Knox and the Roman Catholic theologian and writer Ronald Knox. Dilly studied classics at Eton and then at King’s College, Cambridge, where he became a fellow. He was a papyrologist, working on fragmentary Greek texts, and a classicist of considerable reputation. He was also, by all accounts, an unconventional, absent-minded, and intensely driven individual.

Room 40: World War I

Shortly after the outbreak of World War I in 1914, Knox was recruited to the Room 40 codebreaking operation of the Admiralty. Working in the cramped, eccentric environment of naval intelligence, he proved an inspired cryptanalyst.

His most celebrated Room 40 contribution was helping decrypt the Zimmermann Telegram in 1917 – the German foreign ministry’s instruction to its Mexican ambassador to propose a wartime alliance against the United States. The telegram’s disclosure helped bring the United States into the war.

Knox was also known in Room 40 for his insistence on having a bathtub installed in an adjacent room (Room 53) in the Admiralty Old Building, where he would soak and think. This became something of a legend.

GC&CS and the Interwar Period

When Room 40 was merged with the War Office’s MI1b in 1919 to create the Government Code and Cypher School (GC&CS), Knox joined the new organisation and remained there for the rest of his career.

During the 1920s and 1930s he worked on a range of cipher problems. He developed “rodding” – an algebraic technique for analysing rotor cipher machines – and applied it to early Enigma work with partial success.

On 24 April 1937, Knox achieved a notable breakthrough: he cracked the Spanish Enigma (the commercial Enigma used by Franco’s Nationalist forces during the Civil War). However, the intelligence was not shared with the Republican side.

By the outbreak of World War II, Knox was GC&CS’s chief cryptanalyst.

The Enigma Problem and the Polish Solution

Knox had worked on the military Enigma for years. His failure to crack it was not for want of effort or intelligence: the problem was his assumptions. Like most GC&CS analysts, he assumed the military Enigma wired its entry drum in keyboard order (QWERTZU), as the commercial version did. This assumption was wrong.

When Bertrand had brought Schmidt’s Enigma documents to GC&CS in the early 1930s, Knox and GC&CS were unable to exploit them. The documents provided operating procedures and key tables, but without the correct mathematical framework, they were not sufficient.

The Pyry Conference (25–26 July 1939):

Knox was a member of the British delegation at the Polish Cipher Bureau’s facility in the Kabaty Woods near Pyry. He and Commander Alastair Denniston (GC&CS head) arrived expecting a technical discussion of difficulties and approaches. Instead the Poles announced they had been reading German military Enigma traffic since 1933.

Knox’s reaction was complex and has become one of the memorable moments in cryptographic history:

  • He was furious – not at the Poles, but at himself – upon learning that the military Enigma used simple alphabetical wiring (ABCDEFG…) for the entry drum. This was the assumption he had dismissed as too obvious to bother testing.
  • He reportedly threw a tantrum directed at his own earlier decision to reject this possibility.
  • Yet he grasped everything very quickly, almost quick as lightning (Rejewski’s words).
  • He was, in the description that has stuck, “chagrined – but grateful.”

After the meeting, Knox sent the Polish cryptologists a gracious note in Polish on official British government stationery, accompanied by a scarf featuring a picture of a Derby winner and a set of paper “batons” – a gesture of acknowledgement and thanks.

As his GC&CS colleague Peter Twinn later said: “It was such an obvious thing to do, rather a silly thing to do, that nobody – not Dilly Knox or Tony Kendrick or Alan Turing – ever thought it worthwhile trying.”

Wartime Contributions

Despite his disappointment over the Enigma entry drum, Knox contributed substantially to the British Enigma effort:

Abwehr Enigma: In October 1941, Knox solved the Abwehr Enigma – the cipher used by German military intelligence (the Abwehr) in their field operations. This was a technical tour de force: Knox cracked it without knowing the machine’s internal wiring, working purely from ciphertext analysis. The resulting operation, Intelligence Services Knox (ISK), decrypted Abwehr communications throughout the war. By the end of the war, ISK had decrypted and disseminated 140,800 messages. Intelligence from these decrypts played a critical role in the Double-Cross System (MI5/MI6’s turning of German agents) and in Operation Fortitude (the D-Day deception campaign).

Knox also worked on Italian naval Enigma variants, contributing to intelligence that aided British operations in the Mediterranean.

Staffing: Knox ran his section with characteristic eccentricity. He preferred to recruit women – “Dilly’s girls” – including Mavis Lever (later Batey) and Margaret Rock. Both made independent significant contributions to Enigma cryptanalysis.

Death

Knox was seriously ill from lymphoma (cancer) from early 1942. He continued working for as long as he was physically able, supervising ISK from his sickbed. Peter Twinn took over the day-to-day running of ISK as Knox declined.

Knox died on 27 February 1943, aged 58. He died knowing the Abwehr Enigma had been broken but before he could see the full fruits of Ultra intelligence in the war’s decisive campaigns.

He was awarded the CMG (Companion of the Order of St Michael and St George).

Relationship to the Polish Codebreakers

Knox represents the road not taken – the brilliant British analyst who was within reach of the Enigma solution but failed to find it, while the Poles succeeded by being bolder in their assumptions and more rigorous in their mathematics.

His reaction at Pyry is historically significant not as a moment of pettiness but as a measure of what was at stake: a man of genuine brilliance, who had devoted years to the Enigma problem, learning in a single afternoon that three Polish mathematicians had solved it seven years earlier using a method he had dismissed.

That he responded with graciousness – the note in Polish, the acknowledgement, the immediate recognition of the Polish achievement – says something important about him.

Sources