Ok, here I was thinking the cadillac would be lowered by a heavy steel chain, miles long, and a powerful wynch, attached via the arm of a crane to a tugboat. The chain could possibly be made of tungsten, or adamantium, or Superman, if he temporarily gained Mr Fantastic's (Fantastic Four) stretching abilities, for that matter, since it was a hypothetical example
Yes, even in the deepest oceans, cadillacs do not float for very long...sigh.