He assisted Turing with the enigma code breaking
Extracts from Obituary 19 Nov 2004- The Guardian below:
Twinn was the first mathematician recruited by British intelligence before the second world war to attack German ciphers. He was also the first person to break open a signal encoded by an Enigma machine.
Decryption skills painstakingly developed in Room 40 of the old Admiralty building, where throughout the first world war naval intelligence had brilliantly exploited a captured German naval codebook, were allowed almost to wither away after 1918. But under the aegis of the Foreign Office, a handful of Room 40 veterans set up, on a shoestring, a Government Code and Cipher School (GC&CS) in Victoria. In wartime, its HQ moved to a requisitioned Victorian villa at Bletchley Park in Buckinghamshire, scene of extraordinary expansion.
After the war, GC&CS developed into the current Government Communications Headquarters.
Twinn was born in Streatham, the son of a senior Post Office administrator. He went to school at Manchester Grammar and Dulwich College, and read mathematics at Oxford, winning a scholarship for a higher degree in physics but with no clear idea of a career.
Twinn assisted Turing in organising Hut 4's assault on naval Enigma (each major German command used different ciphers) while Knox turned to the Abwehr, German military intelligence. When Knox fell ill with cancer, Twinn took over the Abwehr operation, which underpinned the elaborate allied disinformation campaign that successfully masked the plans for the invasion of Normandy in June 1944 (Churchill's "bodyguard of lies").
At this time he married Rosamund Case, a GC&CS colleague who shared his love of music and played the cello.
His impressive intellectual versatility included musical composition, virtuosity on the clarinet and the viola, and an interest in insects; to photograph them he borrowed the RAE's special cameras. He studied part-time for a PhD in entomology from London University, helping to produce a standard work on beetles.
His entry at the Bletchley Park "Hall of Fame" on the link below