To withstand the pressure over 14,000 feet down, the submersible Alvin's hull is this metal, about 2 inches thick
Imagine for a moment that the Sub has 1/12 inch thick hull and is a 
cube, ...... weighs the boat down further, so you end up with a complete pressure 
hull... [DOC] [TLE] The Quest to Map Titanic : Woods Hole Oceanographic Institution [PAR] Apr 12, 2012 ...