Peter Twinn

Twinn became interested in entomology, gaining his doctorate from the University of London in the jumping mechanism of click beetles. He co-authored A Provisional Atlas of the Longhorn Beetle (Coleoptera Cerambycidae) (1999), a study of the distribution of a number of beetle species.

Twinn's carried on government work after the war in a number of departments, including, in the late 1960s, as Director of Hovercraft in the Ministry for Technology. Later he became Secretary of the Royal Aircraft Establishment in Farnborough. In the early 1970s, he was the second secretary of the Natural Environment Research Council. He was appointed CBE in the 1980 Birthday Honours.

Twinn had an interest in music and played the clarinet and viola. Twinn married Rosamund Case, whom he had met at Bletchley Park through his interest in music, in 1944; they had a son and three daughters.

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

In early 1940 Twinn made the first break into Enigma. This could have been done much earlier if only they had tried the alphabetical system detailed in the patent application.

Twinn was the first professional mathematician to join GC&CS. In early 1939, he applied after seeing an advertisement, working first in London before moving to Bletchley Park. He worked with Dilly Knox and Alan Turing on German Enigma ciphers. In early 1942, he became the head of the Abwehr Enigma section.

Twinn was the first British cryptographer to read a German military Enigma message, having obtained vital information from Polish cryptanalysts in July 1939. Twinn said that "It was a trifling exercise, but I repeat for the umpteenth time, no credit to me."

In July 1939 GC&CS moved from London to Bletchley Park. The mansion in the park was used by the staff, but many other buildings had to be constructed to accommodate the large number of people who worked for GC&CS during the war. These temporary buildings were known as the "huts".

In July 1939, a month or so before the war started, Knox and some others travelled to Poland. Polish cryptologists, some of whom were brilliant, handed over to their British colleagues key information about Enigma, including replica machines.

In December 1938 the Germans added additional rotors (up to six) and the number of combinations increased dramatically. The Germans believed that messages sent on their most sophisticated Enigma machines were so well coded that they could not be decoded. But Twinn and his colleagues proved them wrong.

In the meantime, Koch had set up a company with the hope of selling his encryption machine for commercial use; one disadvantage was that numbers had to be spelt out in words. Industry was not interested, but in 1926 the German Navy looked at the Koch machine. Senior officers were impressed with it and ordered a large number. The purchase of the device – called Enigma – was kept strictly secret.

The British codebreakers had been working on the commercial version of Enigma, the easier of the two to break, during the 1920s and 1930s, and they had made much progress in breaking the military version. But Twinn and his colleagues were stymied because they could not work out the order in which the Enigma keys were wired up.

The Enigma machine dated back to 1919, when Hugo Alexander Koch, a Dutchman, patented an invention that he called a secret writing machine. Soon Arthur Scherbius, an engineer, was experimenting with this and similar machines and became enthusiastic about encryption machines that used rotors. He recommended them to Siegfried Turkel, the director of the Institute of Criminology in Vienna, who also became interested in them.

Peter Frank George Twinn CBE (9 January 1916 – 29 October 2004) was a British mathematician, Second World War codebreaker and entomologist. The first professional mathematician to be recruited to GC&CS. Head of ISK from 1943, the unit responsible for decrypting over 100,000 Abwehr communications.