Rather then punt an old thread...
It turns out the story is true. During WWII the games were sold in wooden boxes and 'the bank' also had a wooden tray with partitions for the different denominations. Hidden in the 'lid' of the box were compartments that housed metal files and maps compasses and such. Here is the part that surprised me...
The games also included a plastic relief map compressed for storage but once separated and exposed to air the map would expand in 3D. This would allow prisoners of war to use a light near the edge of the map to simulate sun angles and shadow spots so they could remain harder to spot.
Other details...
A pencil 'hob' (pocket clamp attachment for pencils) was magnetized and acted as a compass. You rested the center of mass over the pencil lead and it indicated magnetic North.
Hoyle produced playing decks of cards with an ultrathin layer backing that could be seperated from the Kings and Queens (love the Brits) and then unfolded into maps.
Chess/cribbage/backgammon sets had secret radio components hidden within the different playing pieces.
The man chosen for the position of creating these little joy packages was selected for the job because he once challenged Harry Houdini to perform an escape under carefully controlled circumstances. Houdini foiled his plans by bribing the man creating his 'cage' (actually a box) but thats beside the point.
