Das Boot...
Always watch foreign movies in the original. That's a rule I've learned from anime (which I like a lot).
And Apocalypse Now was a brilliant film, really entertaining. Only political paranoids (who see communists undre their beds, just like the Jesus freaks who see Satan behind everything they don't like) might find it offensive. Try Joseph Conrad's "Heart of Darkness," the book it was based on. A really great read, as well.
No doubt about it. The subtitles are distracting for about 10 minutes, then you adjust and forget they're there. And you gain so much, like the original spoken inflections of the original actors, which is important. Plus in the case of Das Boot, there were a lot of incidental sounds that the boom mics picked up but that weren't there in the dubbed version. They were all removed along with the dialog. If a chair creaked or a paper crumpled, it either wasn't there or it was replicated with a cheezy ex-post-facto foley approximation. Without those sounds you lose a lot of the original's ambiance.
Only political paranoids (who see communists undre their beds
I'm no Bircher, but my ideological radar is still pretty finely tuned. However, the film is such a stroke of genius that I readily forgive its lefty overtones.
Regarding Heart of Darkness, I read it about two years ago. Good stuff. I've forgotten most of it, but I still remember that line about the african locals with their scrawny arms and their joints that looked like "knots in a rope".