Twenty years ago, back at Newton I did ask one of the Kennel Maids where the dogs came from. It seems many were donated by owners who couldn't handle them. The dogs were assessed for suitability but the deciding factor was often the state of the dogs hips. As working dogs the RAF would only accept dogs that had the best scores, some were re-homed, the remainder destroyed. The smell of singed fur coming from the dog crematorium wasn't pleasant.