Despite the extra length, I would *strongly* recommend the mini-series version. I first watched this when it came out on TV as a mini-series (293 min, 1985), then recently as the movie version (149 min, 1981), and then the mini-series again.
In cutting the length down for the movie version, what largely remains are action scenes. Retained in the mini-series version are the quieter more reflective, atmospheric scenes, which in my opinion are what most make Das Boot truly AWESOME. These scenes gradually and subtly develop the characterizations of the crew members: their divergent political beliefs, the tensions among them, their cynicism or honor, their bravery or fragility. The submarine itself is a central character too: emerging through the depths like a great lethal whale, or plowing through the spray in rough weather, or floating calmly across the placid ocean surface, all to the backdrop of the haunting and memorable theme music. These subtle atmospheric aspects are what most stayed with me for 30 years. I would also suggest watching it in German with subtitles - one of the things that makes this an unusual WWII movie is that it is from the German perspective, and hearing it in German gives a more intense feel for that Germanic aspect and its special qualities (even if you don't understand German). Das Boot is an amazing experience, and it is well worth immersing yourself in the original full length miniseries version for a memorable and unique experience.
In cutting the length down for the movie version, what largely remains are action scenes. Retained in the mini-series version are the quieter more reflective, atmospheric scenes, which in my opinion are what most make Das Boot truly AWESOME. These scenes gradually and subtly develop the characterizations of the crew members: their divergent political beliefs, the tensions among them, their cynicism or honor, their bravery or fragility. The submarine itself is a central character too: emerging through the depths like a great lethal whale, or plowing through the spray in rough weather, or floating calmly across the placid ocean surface, all to the backdrop of the haunting and memorable theme music. These subtle atmospheric aspects are what most stayed with me for 30 years. I would also suggest watching it in German with subtitles - one of the things that makes this an unusual WWII movie is that it is from the German perspective, and hearing it in German gives a more intense feel for that Germanic aspect and its special qualities (even if you don't understand German). Das Boot is an amazing experience, and it is well worth immersing yourself in the original full length miniseries version for a memorable and unique experience.