The Colditz glider really flew.
Documentary on TV tonight. Experimental team built a glider to the same design and materials, then launched it off the roof of the castle using a bath full of bricks as a launch accelerator.
To be fair, the glider was remotely controlled for its twenty or so second flight, but it did launch, it did cross the river and it did avoid the town. It's rather untidy landing was more or less deliberate, to prevent it overflying private property. In 1945 that area was completely clear of obstruction.
So, it seems the Colditz prisoners were justified in believing that it would have flown. Nice one guys.
Roger.