I was watching NCIS at someone's house last Sunday and they're inside a Navy sub looking for an enemy agent. Biggest damn sub I ever saw. A real sub is so cramped and tiny that a 6'4" 220 lb guy is going to have trouble finding anywhere to stand fully erect or lay down and stretch out and if you walk towards one another in a passageway, one of you will have to get out of the passageway because there isn't enough room to sidle past each other. I mean, it's cramped! A regular ship is cramped as hell but that's nothing compared to a sub. But on this NCIS episode, they miraculously had all kinds of room. They tried to make it look cramped but it was actually still far more spacious than a real sub.