HMS Marulken has been my obsession the past few days and since it's not a really well known game I though I'd put it out to you guys. The main gamemode is the campaign demo which you have to sink a specific ship called the Z18 Jaeger. One submarine is a crew and a crew can have up to 4 people but you can have multiple crews within one game at the same time.
It's a fun game that's difficult to learn at first but once you figure it out it's really easy. I've been playing a lot lately so if you want to play hit me up.