Might I suggest asking Ringo about the engine room, refueling the tank, and maybe about how to operate the console etc?

: So Ringo, how exactly does this submarine work?

: Well all sorts of crazy mechanical nonsense. George is the mechanic, I just fill 'er up.

: Oh. Well how exactly do I do that?

: You open the fuel tank. Seems to be stuck at the moment.

: Does the missing key in the console have anything to do about it?

: Probably. That key unlocks the fuel tanks.

: Do you know where I could...find it?

: Ask John.

: Thanks for the help, I guess.