To withstand the pressure over 14,000 feet down, the submersible Alvin's hull is this metal, about 2 inches thick
[DOC] [TLE] Full text of "The ocean engineering program of the U.S. Navy ... [PAR] 1 2 THE NAVY OCEAN ENGINEERING PROGRAM In recognition of the 
magnitude .... ALVIN, a deep-submergence vehicle capable of working in depths 
of 6000 ft It is ... High- strength steels or titanium will be developed for the 
pressure hull, and .....