I'm doing a project around The Great Escape from 1963 and looking at other POW escape films. I seem to remember one (but I may be totally mis-remembering) in which the escapees use the diversion of a stage play or variety show to escape underneath the theater after they go behind stage just before the curtain call. I recall they play a record to cover their escape and the last shot is of the stage or curtain with the record playing on and on. I thought it might be The McKenzie Break, which I hadn't seen since 1970, but it's not. It's not The Colditz Story (although there they do escape from beneath a stage). I haven't seen John Huston's Victory in ages but summaries on-line say they escape from a shower room, not under the theater.