It’s not the “somebody’s secretly gay on a submarine” gag that has the impact in this one, I think.  It’s the fact that the indicator is so vague.  They could just be missing a card.  I’ve never served on a submarine but I’m guessing that there’s the same kind of homophobic background tension as a high school locker room.  I imagine them looking at each other after the third panel.  They’re going to tear that ship apart until they find the jack.

There’s also the possibility that the guy who told the story hid the jack as a joke.  And maybe in someone’s bunk.