Top mathematician solves WW2 letters cipher mystery
30 April 2013 Last updated at 21:11 BST
For 60 years, mysterious coded letters from a British prisoner of war have refused to give up their secrets.
Relatives of imprisoned naval officer John Pryor were unable to discover the hidden messages in the dozens of letters he sent back to his family.
Finally, with the help of a top mathematician, the wartime cipher has been cracked.
Jon Kay reports.