Tolkien, one of his generation’s most respected linguists, was ”earmarked” to crack Nazi codes in the event that Germany declared war.
Intelligence chiefs singled him and a ‘cadre’ of other intellectuals to work at Bletchley Park, the codebreaking centre in Buckinghamshire.
Its staff – which included Alan Turing, the gay codebreaker – would later decipher the ‘impenetrable’ Enigma machines.
This saved Britain from German conquest by allowing the Navy to intercept and destroy Hitler’s U-Boats.
According to previously unseen records, Tolkien trained with the top-secret Government Code and Cypher School (GCCS).
He spent three days at their London HQ in March 1939 – six months before the outbreak of the Second World War and just 18 months after the publication of his first book, The Hobbit.
But although he was ”keen”, Tolkien – a professor of English literature at Oxford University – declined a £500-a-year offer to become a full-time recruit.