I remember spending hours back in the days with 688(i) Hunter/Killer from the guys that later made Dangerous Waters.
The fact it was about simulating "modern" (in comparison to ww2) subs was what attracted me to it, as my favorite subsim ever ( Red Storm Rising) was all about this too.
I skipped Sub Command , that was 688 HK followup (that had much needed higher res panel as in 688 HK it was sometime hard to read the sonars graphics) that featured 2 more subs, using the same engine as 688 HK, for reason i don't remember despite i was interested (especially in the Akula that had some interesting weaponry).
And wanted to buy that Dangerous Water (a big upgrade of SubCom, while always using the same engine again, with new sub, and for once playable warship and aircraft), but after reading some tales about it being very unstable, i refrained until recently.
I have read that Sonalyst ceased to patch it years ago, but is stable now with mods ?
It's a very great game, but i still have crashes from time to time, especially when there are some surface battle between opposed fleets.
(Edit : oh my bad, i was thinking about SubCom, it's Subcom i bought a few years ago, the one with "only" 3 subs not Dangerous Waters )
It's sad that there's no modern subs simulation anymore, it seems ww2 sub sims are still the most popular, maybe it's because modern subs are not about visually acquiring your target anywmore, but are about spending your time watching sonars graphics and calculating fire solution in the TMA , certainly less attractice to gamers, but once you are into it, it's really interesting.
The bips about a torpedo trying to acquire your sub can be a very immersive moment despite the minor visuals.