They actually shot two versions of "The Longest Day", one with the actors speaking their native languages, and they also filmed the scenes with them speaking English, not dubbed. I much prefer to hear the actors in their native tongues with the subtitles.
I believe they actually shot the scenes twice in ‘Das Boot’, once in German and again in English (as mentioned the main actors all spoke English),not much actual dubbing.
This was a point of contention in some of the home theater forums when it came out on DVD. Most movie fans (geeks) want to see the orginal language version of foreign movies with subtitles vs dubbed versions. In ‘Das Boot’ the English version was just as ‘original’ as the German version leaving the ‘orginalist’ geeks confused as to which was the correct version to watch..