[UKönig]

I would very much recommend the novel as a companion to the movie.

Yes, it is a novel, but not a work of fiction. More of an amalgamation of several U-boat missions woven into one story. Herbert Werner of Iron Coffins describes several instances in his own book which are similar to ones told in Das Boot. I cannot praise those books enough. Your own simulated u-boat experience will be all the richer for it, in my opinion.