I recall trying to find it on video many many years back and couldn't find it. It might be out on DVD now though. Be careful though, because I think there's another movie with this exact same title.
So to make sure we're talking about the same movie... the end was aFORTRESS End Spoiler
Gosh, I sure hope that's the film.
I'll wait a bit longer for a confirmation, but I'm 99.99% sure I'm right.... Then I'll post a new pic.