液態金屬
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 (known as SCB 64A) was a variant of , but with numerous detail changes, such as a conning tower, stepped sail, and the BQR-4 passive 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.