Secrets Revealed: Messages from WWII PoWs

Professor David McMullan from Plymouth University came to talk to us in March to tell us how an appeal for help from the family of a serviceman who spent most of WWII in a POW camp led him on a fascinating investigation into the little known secret codes used by British and American prisoners of war to communicate with the Intelligence Services. 

These codes were a rare example of hiding encrypted messages in plain sight - in this case letters home.  Professor McMullan started by giving us a very quick rundown of the history of encryption, with a chance to practice using the Caesar Cipher for ourselves.  He then showed us how the prisoners hid their messages in letters to relatives – we got a chance to practice this technique too.  Even with pencil and paper the exercise was hard enough, but that was a luxury not open to the prisoners who required considerable mental agility to carry out the work in their heads to prevent discovery.

The messages they sent requested materials to help with escape events and also provided information of use to the war effort.  Yet more mysteries remain – who taught the prisoners the coding techniques?  What codes were used later in the war, which despite al Professor McMullan’s ingenuity, remain unbroken?  And most of all what happened to the records of MI9, responsible to helping prisoners escape, which would have revealed much more about this story?  The records of Its American equivalent were destroyed after the war, while those of MI9 went missing.  Was this just bad luck, or were there messages hidden in some of those letters that, if decoded, would still have proved embarrassing to post war governments?

We all thoroughly enjoyed this talk and are both grateful to Professor McMullan for coming to speak to us about it, and full of admiration for his ingenuity in deciphering the code.