A common myth surrounding the bombing (due in part to such books as Winterbotham's "The Ultra Secret") is that Coventry was deliberately undefended to prevent the Germans realising that Enigma cipher machine traffic (information from which was termed Ultra) was being read by British cryptanalysts at Bletchley Park. This claim is untrue – Winston Churchill was aware that a major bombing raid was to take place, but no-one knew where the raid was meant to strike before it was too late to evacuate.