The S4W reactor is a naval reactor

United States Naval reactor

United States Naval reactor refers to nuclear reactors used by the United States Navy aboard certain ships to produce power for propulsion, electric power, catapulting airplanes in aircraft carriers, and a few more minor uses. Such Naval nuclear reactors have a complete power plant associated with...

 used by the United States Navy

United States Navy

The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

 to provide electricity generation

Electricity generation

Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...

 and propulsion

Nuclear marine propulsion

Nuclear marine propulsion is propulsion of a ship by a nuclear reactor. Naval nuclear propulsion is propulsion that specifically refers to naval warships...

 on warship

Warship

A warship is a ship that is built and primarily intended for combat. Warships are usually built in a completely different way from merchant ships. As well as being armed, warships are designed to withstand damage and are usually faster and more maneuvrable than merchant ships...

s. The S4W designation stands for:

• S = Submarine
  Submarine
  A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
  
   platform
• 4 = Fourth generation core
  Nuclear reactor core
  A nuclear reactor core is the portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place.- Description :...
  
   designed by the contractor
• W = Westinghouse
  Westinghouse Electric (1886)
  Westinghouse Electric was an American manufacturing company. It was founded in 1886 as Westinghouse Electric Company and later renamed Westinghouse Electric Corporation by George Westinghouse. The company purchased CBS in 1995 and became CBS Corporation in 1997...
  
   was the contracted designer

This nuclear reactor

Nuclear reactor

A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

 was a variant of the Submarine Fleet Reactor (SFR) with the horizontal steam generator

Steam generator (nuclear power)

Steam generators are heat exchangers used to convert water into steam from heat produced in a nuclear reactor core. They are used in pressurized water reactors between the primary and secondary coolant loops....

s pioneered in S1W

S1W reactor

The S1W reactor was the first prototype naval reactor used by the United States Navy to prove that the technology could be used for electricity generation and propulsion on submarines...

 and S2W

S2W reactor

The S2W reactor is a naval reactor used by the United States Navy to provide electricity generation and propulsion on warships. The S2W designation stands for:* S = Submarine platform* 2 = Second generation core designed by the contractor...

.

Two boats of the Skate class

Skate class submarine

The Skate-class submarines were the United States Navy's first production run of nuclear powered submarines. They were an evolution of the Tang class in everything but their propulsion plants, which were based on the experimental . The four Skate class boats re-introduced stern torpedo tubes...

 were built with S4W reactors: USS Swordfish (SSN-579)

USS Swordfish (SSN-579)

USS Swordfish , a , was the second submarine of the United States Navy named for the swordfish, a large fish with a long, swordlike beak and a high dorsal fin....

  and USS Seadragon (SSN-584)

USS Seadragon (SSN-584)

USS Seadragon , a , was the second ship of the United States Navy to be named for the seadragon, a small fish commonly called the dragonet....

. During later overhauls, the S4W reactors in both subs were replaced with S5W reactors .