Is there any truth in stories that POW's during WWII would write letters and even books with coded messages in them? I remember something about a book that was written inside a German POW camp where the ninth letters spelled out some secrets or other pertaining to enemy positions. Any websites that tell of inventive attempts to Lick Hitler?
They did something like that, if I remember correctly. At the Colditz I remember hearing something about coded messages on music records. I don't know it thats true, but they definately communicated through code to the outside.
Check out tactics used by the Special Operations Executive (and Leo Marks in particular). A quick precis is given at http://www.64-baker-street.org/people_leo_marks_master_spy.html His code-poem, "The Life That I Have", was given to VioletteSzabo - Marks maintained that codes based on well-known poems could be easily broken by the enemy, and he sent agents out with unfamiliar poems, usually written by himself, that nobody else could possibly have known.