"Now we are getting nearer to true submarines," PopSci proclaimed in June 1949 of the Navy's newly revamped U.S.S. TUSK, "not just buttoned-up surface ships that can dunk for a few hours." The TUSK, first commissioned as a torpedo boat in 1946, reemerged as a deadly spy sub capable of remaining in the deep for weeks, thanks to a snorkel that allowed its diesel engines to run underwater while its upgraded batteries recharged. This technology and a sleek aircraft-inspired design improved the sub's speed from 10 knots to 15 knots. For the next two decades, the TUSK patrolled the Mediterranean Sea, eavesdropping on Eastern Bloc communications. Today the 60-year-old vessel still operates as a training ship, a living ancestor of the new generation of spy subs equipped with docks for unmanned submersibles and (nearly) silent propulsion.