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:
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) [1] and USS Seadragon (SSN-584) [2].
References
S4W reactor Wikipedia(Text) CC BY-SA