I expected K-19 to be further up the list - or at least get a mention. My naive metric for realism roughly translates to 'How much does this feel like a documentary?' - and K-19, in spite of the big names, certainly felt like a story being re-told.

I think one person mentioned it. But agree. Other sub movies I enjoyed a lot like Hunt for Red October but they're pretty much movies versus realistic.

I know a retired nuke submariner very well. He says modern subs are luxurious compared to U-boats in Das Boot, but feeling is 100% true even today. You can make a sub more spacious, but that won’t make it less claustrophobic.