What exactly are you looking for in a sub sim? Do you mean playing as a crew member onboard a submarine, or do you mean a strategy or sim-style where you direct the sub from a 3rd person view e ? Are you looking for combat, exploration etc.. ?
I'm not familiar with many submarine games however if you've not yet looked at Subnautica, its an exceptional first person diving/survival/exploration title on an alien world - you can eventually construct multiple vehicles including both a mini-sub and a full size one; the latter has a full interior with room for different features, storage and more.
I clicked on this thinking it was something to do with small memory modules haha. I had to read - and think about for a sec - the second reply before I figured out it was submarines. Use of the word "submarine" gave it away for me. <light bulb goes on over head>
Silent Hunter 4 and Silent Hunter 5 both work on Windows 10 - I have both currently installed and working on Win 10 Pro.
4 is set in the Pacific controlling a US sub, 5 in the Atlantic controlling a German U-boat. As commented by termite - some people really don't like the game mechanics of 5 - mainly direct control of the captain and moving around the ship etc.
However you can get quite a few mod's for both and probably still SH3.
Off the top of my head - for v4 have a look at the Real Fleet Boat mod and Run Silent, Run Deep.
For v5 I suggest The Wolves of Steel as a good place to start and I have a gut feeling there are some mods that completely change the 1st person control of the captain - in fact I think there are mods that may remove that completely from the game and revert things back to more like SH4. Even with that stuff in the game you can use hot keys and the in game menu to jump around control positions, but I do agree that v5 is different to previous versions a bit.
Cold Waters is a modern option - but note it's all played from a 3rd person perspective - so it does feel a bit more removed from the action than a traditional 1st person perspective sub sim.
A good place to start with the Silent Hunter series is: http://www.subsim.com/radioroom/index.php
- esp. for looking up releases of new mods and maybe getting a better feel for what other mods people are using with the games.
Yeah, one caveat to my comment about SH5. I purchased it at launch, and it was a buggy, broken mess. There were also huge issues with the Ubisoft authentication servers around the same time. I only put about 10-15 hours in before uninstalling and moving to my junk folder.
The game was too new for any real mods and or fixes/patches to make the game better. I'm would not be surprised if Subsim and the mod community at least made the game playable. So take anger for the game with a grain of salt.
There is also Uboot that is still in development which the one I am waiting on...
Its a cross between SH5, Cold Waters and Fallout Shelter (as use have to manage your crew -make sure Franz doesn't burn the bratwurst or Karl is not too tired + overworked that he drops one of the torpedoes. Which would be bad).
With mods, SH3 is still great. Aside from a few problems SH4 is also good. (As in constant plane attacks for one, But that and other flaws are fixable with mods) The ONE game i'd love to see a remake of is the Great Naval Battle series. Is just a surface ship sim, but spent many hours playing it long ago.
If exploring the deep seas is your thing, you might be interested in Subnautica. Yes, you can build and pilot both a mini-sub as well as a full-scale submarine that will be your mobile base later in the game.
Its a cross between Fallout Shelter and Silent Hunter.
Subnautica really isn't a submarine game, its a sci-fi deep ocean survival game that has subs in it. Still an excellent recommendation and there is an add-on coming soon taking place in an arctic environment.