What seemed like innocent, even mundane, letters home from a World War II prisoner of war to his family contained secret intelligence that is only now being revealed.
Sub Lieut. John Pryor's letters -- which touch on topics like gardening and vegetable patches -- contained messages for the British military and a secret code that died with him.
Now, the veteran's son and a team of historians and mathematicians have finally cracked that code, unearthing encrypted information and supply requests in letters sent from a German POW camp to his family in Cornwall, England.
Mark Phillips shows how the code was broken and what it revealed Friday morning on "CBS This Morning."