I've just watched this again which I recorded at the weekend and it's not bad, in a slightly strange way. It's a kind of combination of a prisoner of war film with a heist, the camp is in probably the best ever location for one, a sunny Greek island. It's a good cast, Roger Moore, Telly Savalas, David Niven, Elliott Gould, Richard Rowntree, Sonny Bono, Stephanie Powers, Anthony Valentine and Claudia Cardinale.
It's a bit improbable but a good way of my passing a couple of hours on. I think it was influenced a bit by Kelly's Heroes, with the end being a bit Bond ish, with the underground bunker exploding. The location also put you in mind of a Bond film too.