RE: How deep can they go?
How about Operation Petticoat...
The guest wakes up in the officers' quarters and doesn't know the sub has dived.
At something the captain says he gets wide-eyed and says,
"We're under? What if we can't..." (gets scared...motions up)
"Oh!" says the captain. "If we can't...
(captain motions up),
then we
(motions
waaay
down ! )
."