The S4W reactor is a naval reactor plant used by the United States Navy to provide electricity generation and propulsion on warships. The S4W designation stands for: * S = Submarine platform * 4 = Fourth generation core designed by the contractor * W = Westinghouse was the contracted designer This nuclear reactor plant utilized an S3W reactor in an alternate equipment arrangement. Two boats of the Skate class were built with S4W reactor plants: USS Swordfish (SSN-579) and USS Seadragon (SSN-584) .