Many people are familiar with the board game Monopoly.
Since it was invented in 1933, over 200 million sets have been sold in 80 countries, and an estimated 500 million people have played the game.
Less well known, however, is Monopoly's role in helping Allied prisoners of war (POWs) to escape from Germany in World War II.
During World War II, about 135,000 British and 95,000 American POWs were held by Germany.
In 1941, the British secret service devised a plan to smuggle maps and other escape tools to Allied POWs.
Detailed maps of Germany, Italy, Norway, and Sweden did exist, but paper maps made too much noise and were hard to fold and conceal.
For an alternative, British intelligence consulted John Waddington Ltd.
, a company that had developed a process of printing on silk and in fact was already producing silk escape maps for British airmen to carry on missions.
Silk made no noise, could be easily concealed in a pocket or pack of cigarettes, and did not disintegrate in the rain.
Next, the Allies needed a way to get the maps to the POWs.
Here, again, Waddington provided a ready answer.
The company was the licensed manufacturer of Monopoly game boards outside the United States.
Although the Germans severely restricted communication with the prisoners, they did allow certain categories of Red Cross care packages to go through.
Games and pastimes were one of the categories.
Monopoly was well known by that time, and detailed silk maps of the area surrounding each POW camp were hidden in some of the games delivered to the POWs.
The designated game sets had a tiny red dot in the corner of the Free Parking square, designed to look like an ordinary printing glitch.
Allied military personnel were briefed on this before their missions.
The map was hidden in a wooden red hotel game piece.
There were also two metal pieces that screwed together to form a file, and a tiny compass hidden inside the dog game piece.
Additionally, under the stacks of Monopoly money was actual German, Italian, and French currency.
An estimated 35,000 POWs escaped during the war, and undoubtedly some of them were helped by these 'Get Out of Jail Free cards.
' The existence of the special Monopoly sets was a closely guarded secret and has only recently become public knowledge.
During the war, the sets were constructed in a secure room, unknown to the rest of the company employees, where skilled craftsmen carved holes in the game pieces to conceal the aids.
The company and the Allies maintained strict secrecy about the scheme, partly because Waddington feared reprisals from German bombs.
After the war, all of the sets were destroyed, and everyone involved in the plan, including the escaped prisoners, was sworn to secrecy.
The British wanted to be able to use the plan again if it became necessary during the Cold War or another conflict.
The secrecy was maintained under the British Official Secrets Act until 2007.
At that time the plan was declassified, and surviving craftsmen and Waddington itself were honored in a public ceremony.