After he reached Britain, Blake joined the Royal Navy as a sub-lieutenant before being recruited by the Secret Intelligence Service (MI6) in 1944. For the rest of the war, Blake was employed in the Dutch Section. He intended to marry an MI6 secretary, Iris Peake, but her family prevented the marriage because of Blake's Jewish background and the relationship ended. In 1946, he was posted to Hamburg and put in charge of the interrogation of German U-boat captains. In 1947, the Navy sent Blake to study languages, including Russian, at Downing College, Cambridge, where his fellow students included the future foreign policy analyst Michael MccGwire. He was posted thereafter to the British legation in Seoul, South Korea, under Vyvyan Holt, arriving on 6 November 1948. Under cover as a vice-consul, Blake's mission was to gather intelligence on Communist North Korea, Communist China, and the Soviet Far East.