The USS THRESHER was the lead ship of the world's most advanced class of nuclear-powered attack submarines.  It had a single, seven bladed propeller that was designed to give little or no cavitation at all speeds when submerged.  It was a true submersible and very poor at traveling on the surface hence the term "boat" did not apply as readily to this ship as it did to her preceeding namesake of USS THRESHER (SS 200) of WW II fame.

During WW II the THRESHER had a distinguished wartime record of 15 war patrols,
being credited with 146,000 tons of shipping sunk or damaged; surviving the war, it was decommissioned December 1947.   One interesting thing was the same Yeoman that
decommissioned the SS 200 also served on the SSN 593 and retired from the Navy
just prior to the loss of the ship, 10 April of 1963.  He was the only known survivor of both submarines and well aquainted with all that were lost at sea that day which included many shipyard personnel who were lost as well.

SSBN 608, Ethan Allen. Tom Clancy, (not crew member) eat your heart out. The launching of this submarine and sister subs were the greatest deterrent against any enemy nuclear attack. When on patrol in the early 60's, they carried 18 Polaris ICBM's with 4 independently targeted warheads each. Thus the "MAD" cold war was maintained. One of my transportation methods while in Navy.