He joined the Government Code and Cipher School as a Junior Assistant in October 1925 to specialise in Russian codes and ciphers. He was down from King's College London with a First in Russian and was teaching at a preparatory school in Margate. Then a sister of the novelist Charles Morgan said that Russian linguists were needed "at a place in Queen’s Gate". He was assigned to Ernst Fetterlein to work on Soviet diplomatic ciphers, with an Army officer, Capt. A.C. Stuart Smith. The first message he read was from Moscow to the Soviet representative in Washington, about the repudiation of debts by American states. In late 1929 to 1930 he was in the Naval Section attacking Russian Naval Codes, and was sent to Sarafand for a fifteen-month investigation of Black Sea Fleet communications. In 1936 he was made Head of the new Air Section at GC&CS.
At Bletchley Park in World War II he was head of the Air Section. He was awarded a C.M.G. in 1943 and a C.B. in 1958.