USS Seawolf (SSN-575) - Wikipedia

On July 21, 1955, the USS Seawolf was launched. It was the first submarine powered by a liquid metal cooled nuclear reactor. From the article:

"USS Seawolf (SSN-575), a unique submarine, was the third ship of the United States Navy to be named for the seawolf, the second nuclear submarine, and the only US submarine built with a liquid metal cooled (sodium) nuclear reactor known as the Submarine Intermediate Reactor (SIR) or Liquid Metal Fast Reactor (LMFR), later designated S2G. Her overall design was a variant of Nautilus, but with numerous detail changes, such as a conning tower, stepped sail, and the AN/SQS-51 active sonar mounted in the top portion of the bow instead of further below. This sonar arrangement resulted in an unusual bow shape above the water for a U.S. submarine. Her distinctive reactor was later replaced with a standard pressurized water reactor, the replacement process lasting from 12 December 1958 to 30 September 1960."