Iron Wolf VR has been one of my absolute favorite VR titles since the first time I tried it. I thought it was an incredible bargain at the time, with its 1 - 4 player online co-op and a terrifically designed U-boat(ish) submarine comprised of a deck (complete with AA gun), a conning tower, a torpedo room, and the helm.
It just got better. Way better. The most recent update included an engine room and the ability to add a fifth player to attend to it. This is more than just adding another player and some pretty levers to play with, though. They also added the ability to use the engine and generator to recharge the compressed air and the batteries respectively. As an added bonus, they also add a snorkel that will allow the batteries and compressed air to be refreshed at periscope depth, rather than afloat on the far riskier surface.
Iron Wolf VR is available as a highly recommended early access title on Steam at this link. They're asking $19.99 and between you and me, it's worth it.