I remember I was in welding vocational trade school when it became public knowledge that the Russians had actually built a sub mostly out of titanium. Having spent weeks learning to weld the stuff myself I was impressed, but so was everyone else in the class.
My understanding is the Russians actually built a construction hall where the atmosphere was completely inert and put their welders into SCUBA gear to perform all of the titanium hull welds. Remarkable efforts made during the Cold War to find that technological edge.