And it's a good thing she came out, too, because the compartment would have slowly filled with water when the sub fully submerged. As it was, the sub was only four hours into its trip across the Atlantic, heading for Scotland, when the crew found out they had a stowaway. Rather than make the kid swim back, they turned the sub around and dropped her back off at Baltimore.
They apparently couldn't come up with a worse punishment.
For its part, the British Navy was characteristically dry and sarcastic about it all, with Captain Douglas Scobie telling the press:
"Certainly, we can't have that sort of nonsense going on in the British navy. Taking away one of Baltimore's citizens is rather overextending our appreciation of their hospitality."
"Especially one who is already crazier than a cat lady at the age of 17."