Bernhard Bert Trautmann is one of the many Prisoners of War from World War Two to feature in the Great Escapes: Remarkable Second World War Captives event at the National Archives.
The coded message was sent by Peter Gardner in a letter that was addressed to his mother and which accompanied a photo of an old school friend . Above: The tiny coded message with the photo.
The recently unearthed secret missive casts fascinating new light on how - right under their Nazi captors noses - Allied POWs communicated with the intelligence services