To withstand the pressure over 14,000 feet down, the submersible Alvin's hull is this metal, about 2 inches thick
When the visibility 
clears, 50 feet down, Hawkes banks the submarine over a metridium field,... [DOC] [TLE] Deep Submergence Rescue Vehicle DSRV - GlobalSecurity.org [PAR] Jul 7, 2011 ...