The top-secret breaking of the German Enigma code by Alan Turing, and the codebreakers working with him at Bletchley Park, was one of the greatest British coups of the second world war. It helped ships delivering vital supplies to the UK during the darkest days of the war to evade the packs of German U-boats trying to hunt them down, and enabled Britain to rebuild its strength and re-equip its armies in preparation for its bid to expel the Nazi armies from Europe.
Now extraordinary fresh details can be told of how the Royal Navy seized vital cipher information from captured German boats to make the work of the codebreakers possible.
The Enigma machine did not actually send the messages. It was used to transform normal German into gibberish which was then transmitted using morse code over the airwaves. British intercept stations could listen in to these signals, but because they were encoded, they could not understand what was being said.