Hi!
Next to liking subs, I'm a huge boardgame fanatic. I recently found this kickstarter for a game called U-boat leader, as well as Gato-leader. U-boat leader is getting its 2nd edition, so there are already some reviews from the first edition in case you are interested.
These are solitary (1 player) wargames. I haven't played these, but I've played others by the same designer (Hornet Leader, Thunderbolt Apache Leader) and really like those.
https://www.kickstarter.com/projects...-u-boat-leader
I thought I would spread the news in case there are more people that might be interested, as the games can be hard to find, as its a very small publisher.
Hope it's useful!