In 1941, when he was 18, Hilton was recruited by the Foreign Office on the strength of his mathematical ability and knowledge of German (a language he had taught himself in a year), for what was then unspecified secret work. Hilton thought his German was probably not up to scratch. "But I was the only person who turned up at the interview," he recalled, "and they jumped at me and said: 'Yes, you must come'."