Alfred Dillwyn Knox is not a widely recognised name, but his career as one of the UK’s leading cryptologists and codebreakers spanned some 30 years, and two world wars. For much of that time he lived in Naphill, and was a well-known and congenial figure in the locality.

Dilly, as he was known, was born in Oxford on July 23 July, 1884, the fourth of six children of the Revd Edmund Arbuthnott Knox and his first wife, Ellen French.

He went to Eton College as a King’s Scholar, became “Captain of School” and won the school’s main prize for mathematics. In 1903 he went to King’s College at Cambridge University, obtaining a first class degree of the classical tripos.

Early Career

After graduating Dilly remained at King’s College as a classical scholar and editor. Following the outbreak of the first world war he was asked in 1915 to join the cryptanalytical bureau in Room 40 at Admiralty House in London. He proved to be an outstanding cryptographer. He succeeded in breaking much of the German admirals’ flag code by “detecting, with his ear for metre, lines of poetry in the repeated bigrams of a message, which provided a crib.”

He was also involved in what was known as the Zimmermann Telegram episode. In January 1917, the German Foreign Secretary, Arthur Zimmermann, sent a coded telegram to the German minister in Mexico City. This instructed the minister to propose an alliance with Mexico if war broke out between Germany and the United States. The telegram was intercepted by the Admiralty’s cryptanalytical bureau. The message was shown to the United States and helped to bring them into the war.

After the war Dilly continued to work in the field of codebreaking in the renamed Government Code and Cypher School (GCCS), but continued to work on Greek manuscripts whenever he could find the time.

Home in Naphill

On July 21 1920 Dilly married his former secretary Olive Margaret Rickman, and they came to live in Naphill. They bought the house called “Courn’s Wood”, now known as “Cournswood House”, in Clappins Lane in Walters Ash. This is where their two sons, Christopher and Oliver, were born.

The Knox family are fondly remembered by the local people. It is said that in the early 1920’s Dilly would travel from the house to the Wycombe railway station on his motorbike and then during the rail journey study his Greek manuscripts, while other passengers read their newspapers.

He had a brush with the law on May 1 1924 when he was summonsed for “driving a motor-cycle to the common danger of the public in Benjamin Rd, High Wycombe”. He had nearly collided with a cyclist. Dilly was found guilty, fined £2 or 14 days’ imprisonment.

His motor-cycling days were ended when he had a serious road accident which left him with a permanent limp. Dilly then bought a small Austin car and is reputed to have had a habit of coasting down Clappins Lane to see how far he could go before needing to start the engine!

Cournswood House is surrounded by woodland in which there is a memorial stone carved from a Denner Hill boulder to mark the spot where Dilly’s ashes are buried, together with those of his wife Olive. Dilly loved trees and planted many on his estate. He is probably best remembered by the people of Naphill for the Atlantic cedar tree he donated to the village. This was presented on May 6 1935 to commemorate the jubilee of King George V and was planted near to the entrance to the Naphill village hall. As the tree grew larger it became the tradition in the village to decorate it at Christmas-time.

Career in the Inter-war Period

During the 1920s, it is thought that Dilly was engaged in breaking Russian and other diplomatic codes. In about 1926 he was promoted to be one of the three Chief Assistants in GCCS. It was in about 1936 that GCCS started to tackle the Service cyphers of the rising dictator states in Europe. Dilly achieved the great feat of reading an Italian naval Enigma message of 24 April 1937. But it was not until a meeting with the Poles in July 1939, that progress was beginning to be made against the German Enigma code.

It was at that time, whist still working in London, that Dilly began working with the young Alan Turing, their relationship probably being that of master and protégé. It is known that over the weekend of September 29, 1939 Turing was staying with the Knox family at Cournswood House. One can imagine the pair sitting-up late into the night discussing how to break the Enigma code.

Codebreaking in WW2

It was during the early years of the second world war that Dilly Knox made his biggest contribution to codebreaking. He tackled the Enigma machines, the original version of which had been developed in Germany not long after the first world war. The device, with variations, was used by the German and Italian military commands to encode strategic messages before and during World War II.

GCCS moved from London to Bletchey Park in north Buckinghamshire on August 15, 1939, with the cover story that “those working here are part of the aerial defence of London”. Dilly and his Enigma Research team went to Cottage No 3. Dilly set part of the team to follow up the Polish ‘Netz’ method of breaking Enigma. They made the first break by GCCS into German Enigma on about January 20 1940.

At the same time, Dilly encouraged Alan Turing to develop the Bombe machine which was to become the main tool for breaking Enigma keys.

Dilly then concentrated on breaking into Enigma machines that did not have a stecker-board (“stecker” is the German word for “plug”, so plug-board). He trained up a new team of some ten women, who became devoted to him, despite his non-communicative and absent-minded ways; two of them became excellent codebreakers. It was on 28 March 1941 that their reading of the Italian fleet’s Enigma signals in the Mediterranean provided Intelligence which led to the defeat of the Italian fleet at the Battle of Cape Matapan. This was an outstanding feat as the Italian navy sent very few Enigma signals.

Dilly now tackled the Abwehr Enigma. It was a version of Enigma with no plug-board but with fiendishly frequent code-wheel turn-overs. It was in the autumn of 1942 that the regular production of decrypted Abwehr messages began at Bletchley. These messages enabled MI5 to gain a complete mastery of the German spies in the UK, and to establish the very successful double-cross programme.

Dilly Knox was named the Chief Cryptographer of Bletchley Park, but by then he was seriously ill with cancer. He was honoured by appointment to C.M.G (Companion of the Order of St Michael and St George) and died at home on February 27 1943. As he lay dying his brother Ronnie, a Catholic priest, insisted on kneeling outside in prayer. ‘Is that Ronnie still out there bothering God in the passage?’ murmured Dilly.