I remember it from seeing it in the theater in 1977, so the shot above is not an outtake from the film as released theatrically; it was in there (otherwise there wouldn't have been those howls coming from an otherwise highly appreciative crowd).

But I can't vouch that it's in the DVD. In the theatrical release, Roger Moore and Shane Rimmer go topside and the fake backdrop is pretty obvious. I can't recall if this is before or after the two bad-guy subs blow each other up, but it is somewhere during the final stretch of the movie.