Alan Turing was awarded the OBE in 1946. King George VI appointed him an Officer of the Order of the British Empire in recognition of his wartime service.
Turing had worked at Bletchley Park, where he helped British codebreakers attack German ciphers, especially the Enigma system. Much of that work remained classified after the war, so the public could not yet appreciate the full reason for the honour.
OBE means Officer of the Order of the British Empire. It is a rank within the order, not a knighthood. The MBE is a lower rank, while CBE is a higher rank; Turing did not receive either of those honours. He was also never knighted.
His 1946 award was one of several later efforts to recognise his achievements. Turing’s wartime contribution became widely known only decades afterward, helping establish his reputation as both a codebreaker and a pioneer of computer science.