The S5W designation stands for: The S5W was the standard reactor for submarines of the United States Navy from its first use in 1959 on USS Skipjack until the introduction of the Los Angeles-class submarines with S6G reactor in the mid-1970s.
One S5W plant was also used in the United Kingdom on the Royal Navy's first nuclear-powered submarine HMS Dreadnought.
To use the additional power generated by the S5W reactor at higher power levels, steam dumps were constructed in the same S1W building but outside the original submarine style hull.
This pressurized water reactor's simplicity, overdesign, and redundancy was intended for ease of operation and tolerance of battle damage.
These characteristics contributed greatly to the type's reliability, longevity, and excellent safety record.