The effect you describe is typical for movies with multiple languages. You would need subtitles specifically for hearing impaired people, where everything is subtitled, regardless the language spoken (and also sounds being described, like "dog barking" etc.). These kind of subtitles should be marked with the "HI" flag. Then you can recognize them:
And you can also search specifically for it, using the advanced search form:
In the case of Das Boot, I am afraid there is no advice to be given.
Hearing Impaired subs for episodes of Das Boot are simply not available.