He assisted Turing with the "Enigma code" breaking
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, on the study of the jumping mechanism of click beetles.
He later worked as Director of Hovercraft in the Ministry for Technology
(Image below Bletchley Park)