The guards at Nazi prisoner-of-war camps were accustomed to looking for tunnels — so they never thought to look in the attic at Colditz Castle, where, astonishingly, British prisoners had constructed a 19-foot glider from scavenged materials.

They planned to launch it from the roof, using a pulley system driven by a falling bathtub full of concrete. They hoped this would send two men soaring across the River Mulde 60 meters below.

The American army liberated the camp before the glider could be launched, and it was subsequently lost, so for 55 years its designers could only wonder whether the “Colditz Cock” would really have flown. But in 1999 a British aviation company built a full-size replica, and the POWs reunited to watch the launch. It worked.