You will win that bet, Little Hawk. The film DW is recalling, is "The Wooden Horse". If I remember rightly, the internees used a wooden vaulting horse to temporarily store the earth removed by tunneling. I also have a feeling that it was based on a true story, which I may or may not have read back in the seventies.
WLD has a point about "Escape To Victory". Any film which could feature Mike Summerbee on the side of the angels on a football pitch requires a considerable effort of imagination on the part of the viewer. It was a likeable film for small boys at the time, even if it was perhaps the silliest war film ever. I can't learn to hate it as much as "Pearl Harbour" though. It is a bit like introducing an air attack into Peyton Place and pretending it is about a historical event. The film stinks, because it is a tacky pile of chocolate box sentimentality, which trivialises a horrible human tragedy.