The S3W 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 S3W 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
• 3 = Third 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), an advance on the pressurized water reactor

Pressurized water reactor

Pressurized water reactors constitute a large majority of all western nuclear power plants and are one of three types of light water reactor , the other types being boiling water reactors and supercritical water reactors...

 (PWR) plant design employed on the USS Nautilus (SSN-571)

USS Nautilus (SSN-571)

USS Nautilus is the world's first operational nuclear-powered submarine. She was the first vessel to complete a submerged transit beneath the North Pole on August 3, 1958...

. The S3W's major innovation was the adoption of vertical U-tube 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. This concept was further developed in the S5W reactor

S5W reactor

The S5W reactor is a nuclear reactor used by the United States Navy to provide electricity generation and propulsion on warships. The S5W designation stands for:* S = Submarine platform* 5 = Fifth generation core designed by the contractor...

, and is in common use today on commercial PWR power plants.

The USS Halibut (SSGN-587)

USS Halibut (SSGN-587)

USS Halibut , a unique guided missile submarine turned special operations platform, later redesignated as an attack submarine SSN-587, was the second ship of the United States Navy to be named for the halibut.-Operational history:...

 and 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 S3W reactors: USS Skate (SSN-578)

USS Skate (SSN-578)

USS Skate , the third submarine of the United States Navy named for the skate, a type of ray, was the lead ship of the Skate class of nuclear submarines...

  and USS Sargo (SSN-583)

USS Sargo (SSN-583)

USS Sargo , a Skate-class nuclear-powered submarine, was the second ship of the United States Navy to be named for the sargo, a food and game fish of the porgy family, inhabiting coastal waters of the southern United States....

 . During later overhauls, the S3W reactors in both Skate and Sargo were replaced with S5W reactors .

United Kingdom

The HMS Dreadnought (S101)

HMS Dreadnought (S101)

The seventh HMS Dreadnought was the United Kingdom's first nuclear-powered submarine, built by Vickers Armstrongs at Barrow-in-Furness. Launched by Queen Elizabeth II on Trafalgar Day 1960 and commissioned into service with the Royal Navy in April 1963, she continued in service until 1980...

 used the S3W reactor. The boat was itself a copy of the Skipjack Class submarines designed and built in the United States for the U.S. Navy.