I suddenly want a seaQuest DSV RPG!
Isn't that a tad dismissive?
I would expect a submarine (or at least a modern nautical) game to have specialized nautical vehicle rules, nautical ship combat, rules about depth (& thermoclines, and sonar detection for modern settings) how to run combats underwater, including the differences from how you expect normal weapons (or spells) and explosives to work...
It may not need to be a full standalone game, but a serious treatment would probably be a notable supplement for most systems.
What does it need to make it 'submarine based'? Special rules for decompression? I figure any modern-set RPG can be set in a submarine? That's just the adventure plot, surely? Like D&D might be in a castle or a desert.
Isn't that a tad dismissive?
I would expect a submarine (or at least a modern nautical) game to have specialized nautical vehicle rules, nautical ship combat, rules about depth (& thermoclines, and sonar detection for modern settings) how to run combats underwater, including the differences from how you expect normal weapons (or spells) and explosives to work...
It may not need to be a full standalone game, but a serious treatment would probably be a notable supplement for most systems.