The secrets of the Enigma code would have been unravelled long before the Second World War if a woman codebreaker's solution had not been dismissed as "too simplistic'', a new book suggests.
The diagnosis was eventually accepted, but not before vital time had been lost pursuing more complex theories and, with that, the chance of intercepting German messages in preparation for war.
Alan Turing, the Cambridge mathematician who led the team trying to break Enigma, and Dilly Knox, one of his most eminent colleagues, were among the male cryptanalysts sceptical of the woman known as "Mrs B B''. Not until Polish codebreakers provided the same answers was her contribution recognised.
The full identity of Mrs B B was never discovered. Action This Day, edited by Michael Smith and Ralph Erskine in aid of the Bletchley Park Trust, says Mrs B B worked out how the Enigma machine operated without even being given a copy of a "crib sheet" provided by the French secret service.
Hugh Foss, another codebreaker, said: "The Poles gave us the complete answer. It was they who must have thought we were the very stupid ones."