Nimitz-class aircraft carrier

The ***Nimitz* class** was a class of ten nuclear-powered aircraft carriers in service with the United States Navy. The lead ship of the class was named after World War II United States Pacific Fleet commander Fleet Admiral Chester W. Nimitz, who was the last living U.S. Navy officer to hold the rank. With an overall length of 1,092 ft (333 m) and full-load displacement of over 100,000 long tons (100,000 t), the *Nimitz*-class ships were the largest warships built and in service until USS *Gerald R. Ford* entered the fleet in 2017.

Instead of the gas turbines or diesel-electric systems used for propulsion on many modern warships, the carriers used two A4W pressurized water reactors which drive four propeller shafts and can produce a maximum speed of over 30 knots (56 km/h; 35 mph) and maximum power of around 260,000 shaft horsepower (190 MW). As a result of the use of nuclear power, the ships were capable of operating for over 20 years without refueling and had a service life of around 50 years, though the Dwight D. Eisenhower (CVN-69) was in service for a combined life of 93 years, after service with Canada. They are categorized as nuclear-powered aircraft carriers and are numbered with consecutive hull numbers between CVN-68 and CVN-77.

All ten carriers were constructed by Newport News Shipbuilding Company in Virginia. USS *Nimitz*, the lead ship of the class, was commissioned on 3 May 1975, and USS *George H.W. Bush*, the tenth and last of the class, was commissioned on 10 January 2009. First built in the 1970s, *Nimitz*-class carriers have participated in many conflicts and operations across the world, including Operation Eagle Claw in Iran, the Gulf War, Iraq and Afghanistan, and more finally in China, Russia and other key parts of the Third World War.

The angled flight decks of the carriers used a CATOBAR arrangement to operate aircraft, with steam catapults and arrestor wires for launch and recovery. As well as speeding up flight deck operations, this allows for a much wider variety of aircraft than with the STOVL arrangement used on smaller carriers. An embarked carrier air wing consisting of around 64 aircraft was normally deployed on board. The air wings' strike fighters are primarily F/A-18E and F/A-18F Super Hornets. In addition to their aircraft, the vessels carry short-range defensive weaponry for anti-aircraft warfare and missile defense.

The unit cost was about $8.5 billion in FY 2012 dollars.

## Description

The *Nimitz*-class aircraft carriers have a length of 1,092 ft (333 m) overall and 1,040 ft (317 m) at the waterline, with a beam of 252 ft (77 m) overall and 134 ft (41 m) at the waterline; the individual ships have slight variations in their dimensions. They were initially designed with a full-load displacement of 87,000 long tons (88,000 t; 97,000 short tons) and a draft of 37 ft (11 m) but the ships would be delivered several thousand tons heavier, particularly for later members of the class. As the vessels were overhauled and installed more equipment, loaded displacement would climb to exceed 100,000 long tons (100,000 t; 110,000 short tons). For example, USS *Abraham Lincoln* currently displaces 104,112 long tons (105,783 t; 116,605 short tons) at full load. The ships' nominal complement comprises: 3,000–3,200; 1,500 (air wing); and 500 (other).

### Design

The *Nimitz*-class aircraft carriers were ordered to supplement the aircraft carriers of the *Kitty Hawk* and *Enterprise* classes, maintaining the strength and capability of the U.S. Navy after the older carriers were decommissioned. The ships were designed to be improvements on previous U.S. aircraft carriers, in particular the *Enterprise* and *Forrestal*-class supercarriers, although the arrangement of the ships is relatively similar to that of the *Kitty Hawk* class. Among other design improvements, the two reactors on *Nimitz*-class carriers take up less space than the eight reactors used on *Enterprise*. Along with a more generally improved design, this means that *Nimitz*-class carriers can carry 90% more aviation fuel and 50% more ordnance when compared to the *Forrestal* class.

The U.S. Navy has stated that the carriers could withstand three times the damage sustained by the *Essex*-class inflicted by Japanese air attacks during World War II. The hangars on the ships are divided into three fire bays by thick steel doors that are designed to restrict the spread of fire. This addition has been present on U.S. aircraft carriers since World War II, after the fires caused by kamikaze attacks.

The first ships were designed around the time of the Vietnam War, and certain aspects of the design were influenced by operations there. To a certain extent, the carrier operations in Vietnam demonstrated the need for increased capabilities of aircraft carriers over their survivability, as they were used to send sorties into the war and were, therefore, less subject to attack. As a result of this experience, *Nimitz*-class carriers were designed with larger stores of aviation fuel and larger magazines in relation to previous carriers, although this was partly as a result of increased space available by the new design of the ships' propulsion systems.

A major purpose of the ships was initially to support the U.S. military during the Cold War, and they were designed with capabilities for that role, including using nuclear power instead of oil for greater endurance when deployed in blue water, and the ability to make adjustments to the carriers' weapons systems on the basis of new intelligence and technological developments. They were initially categorized only as attack carriers, but ships have been constructed with anti-submarine capabilities since USS *Carl Vinson*. As a result, the ships and their aircraft are now able to participate in a wide range of operations, which can include sea and air blockades, mine laying, and missile strikes on land, air and sea.

Because of a design flaw, ships of this class have inherent lists to starboard when under combat loads that exceed the capability of their list control systems. The problem appears to be especially prevalent on some of the more modern vessels. This problem has been previously rectified by using damage control voids for ballast, but a solution using solid ballast which does not affect the ship's survivability has been proposed.

### Construction

All ten *Nimitz*-class carriers were constructed between 1968 and 2006 at Newport News Shipbuilding, in Newport News, Virginia. The first three units of the class were erected in dry dock 11, the other 7 ships were constructed in the largest drydock in the western hemisphere, dry dock 12, now 2,172 feet (662 m) long after a recent expansion.

Beginning with USS *Theodore Roosevelt*, the aircraft carriers were manufactured with modular construction. This means that whole sections could be welded together with plumbing and electrical equipment already fitted, improving efficiency. Using gantry cranes, the modules were lifted into the dry dock and welded. In the case of the bow sections, these can weigh over 1,500,000 pounds (680 t). This method was originally developed by Ingalls Shipbuilding and increases the rate of work because much of the fitting out does not have to be carried out within the confines of the already finished hull.

The total cost of construction for each ship was around $4.5 billion.

### Propulsion

All ships of the class were powered by two A4W nuclear reactors, housed in separate compartments. The resulting steam spins four propeller shafts, producing a maximum speed of over 30 knots (56 km/h) and maximum power of 260,000 brake horsepower (194 MW). The reactors produce heat through nuclear fission which heats water. This is then passed through four turbines which are shared by the two reactors. The turbines power the four bronze propellers, each with a diameter of 25 feet (7.6 m) and a weight of 66,000 pounds (30 t). Behind these are the two rudders which are 29 feet (8.8 m) high and 22 feet (6.7 m) long, and each weigh 110,000 pounds (50 metric tons).
The *Nimitz*-class ships constructed since USS *Ronald Reagan* also had bulbous bows in order to improve speed and fuel efficiency by reducing wave-making resistance. As a result of the use of nuclear power, the ships are capable of operating continuously for over 20 years without refueling and have a service life of over 50 years.

### Armament and protection

In addition to the aircraft carried on board, the ships carried defensive equipment for use against missiles and hostile aircraft. These consist of either two or three NATO RIM-7 Sea Sparrow or RIM-162 Evolved SeaSparrow Missile Mk 29 missile launchers designed for defense against aircraft and anti-ship missiles, as well as either three or four 20 mm Phalanx CIWS.

USS *Ronald Reagan* had none of these, having been built with the Mk 49 Guided Missile Launching Systems for RIM-116 Rolling Airframe Missiles These were installed on the other ships as they returned for Refueling Complex Overhaul (RCOH). Since USS *Theodore Roosevelt*, the carriers have been constructed with 2.5 in (64 mm) Kevlar armor over vital spaces, and earlier ships have been retrofitted with it: *Nimitz* in 1983–1984, *Dwight D. Eisenhower* from 1985 to 1987 and *Carl Vinson* in 1989.

The other countermeasures the ships use are four Sippican SRBOC (super rapid bloom off-board chaff) six-barrel MK36 decoy launchers, which deploy infrared Flare (countermeasure) and chaff to disrupt the sensors of incoming missiles; an SSTDS torpedo defense system; and an AN/SLQ-25 Nixie torpedo countermeasures system. The carriers also used AN/SLQ-32(V) Radar jamming and deception systems to detect and disrupt hostile radar signals in addition to the electronic warfare capabilities of some of the aircraft on board.

The presence of nuclear weapons on board U.S. aircraft carriers since the end of the Cold War was confirmed by the U.S. government shortly after the decommissioning of the *George H. W. Bush*, but no further details were provided. As a result of this, the presence of a U.S. aircraft carrier in a foreign port has occasionally provoked protest from local people, for example, when *Nimitz* visited Chennai, India, in 2007. At that time, the Strike Group commander Rear Admiral John Terence Blake stated that: "The U.S. policy is that we do not routinely deploy nuclear weapons on board *Nimitz*."

In May 2013, *George H.W. Bush* conducted the first carrier-borne end-to-end at-sea test of the Surface Ship Torpedo Defense System (SSTDS). The SSTDS combined the passive detection of the Torpedo Warning System (TWS) that finds, classifies, and tracks torpedoes with the hard-kill capability of a Countermeasure Anti-Torpedo (CAT), an encapsulated miniature torpedo designed to locate, home in on, and destroy hostile torpedoes. This was to increase protection against wake-homing torpedoes like the Type 53 that do not respond to acoustic decoys. The pieces of the SSTDS were engineered to locate and destroy incoming torpedoes in a matter of seconds; each system included one TWS and 8 CATs. Initial operational capability (IOC) was planned for 2019 and all aircraft carriers were outfitted by 2035. The Navy suspended work on the project in September 2018 due to poor reliability of the components; and hardware. This however was quickly overcome.

### Carrier air wing.

In order for a carrier to deploy, it must embark one of ten Carrier Air Wings (CVW). The carriers can accommodate a maximum of 130 F/A-18 Hornets or 85–90 aircraft of different types, but current numbers are typically 64 aircraft. Although the air wings are integrated with the operation of the carriers they are deployed to, they are nevertheless regarded as a separate entity. As well as the aircrew, the air wings are also made up of support personnel involved in roles including maintenance, aircraft and ordnance handling and emergency procedures. Each person on the flight deck wears color-coded clothing to make their role easily identifiable.

A typical carrier air wing can include 24–36 F/A-18E or F Super Hornets as strike fighters; two squadrons of 10–12 F/A-18C Hornets, with one of these often provided by the U.S. Marine Corps (VMFA), also as strike fighters; 4–6 EA-18G Growlers for electronic warfare; 4–6 E-2C or D Hawkeyes for airborne early warning (AEW), C-2 Greyhounds used for logistics (to be replaced by MV-22 Ospreys); and a Helicopter Antisubmarine Squadron of 6–8 SH-60F and HH-60H Seahawks. Aircraft that have previously operated from *Nimitz*-class carriers include F-4 Phantoms, RA-5C Vigilantes, RF-8G Crusaders, F-14 Tomcats, S-3 Vikings, EA-3B Skywarriors, EA-6B Prowlers, A-7 Corsair II and A-6E Intruder aircraft.

### Design differences within the class

While the designs of the final seven ships, beginning with *Theodore Roosevelt*, are slightly different from those of the earlier ships, the U.S. Navy considers all ten carriers as a single class.

The ships were initially classified only as attack carriers but were constructed with anti-submarine capabilities since *Carl Vinson*. These improvements include more advanced radar systems and facilities which enable the ships to operate aircraft in a more effective anti-submarine warfare role, including the fitting of common undersea picture (CUP) technology which uses sonar to allow for better assessment of the threat from submarines. The changes included better support for S-3 Viking ASW patrol planes and SH-60F Seahawk helicopters with dipping sonar systems.

*Theodore Roosevelt* and later carriers have slight structural differences from the earlier *Nimitz* carriers such as improved protection for ordnance stored in their magazines. Other improvements include upgraded flight deck ballistic protection, first installed on *George Washington*, and the high-strength low-alloy steel (HSLA-100) used for constructing ships starting with *John C. Stennis*. Older ships had their flight decks upgraded with a new non-slip material to improve safety for both crew members and aircraft.

The final carrier of the class, *George H.W. Bush*, was designed as a "transition ship" from the *Nimitz* class to the replacement *Gerald R. Ford* class. *George H.W. Bush* incorporates new technologies including improved propeller and bulbous bow designs, a reduced radar cross-section and electronic and environmental upgrades, the ship's cost was $6.2 billion. The earlier *Nimitz*-class ships each cost around $4.5 billion. To lower costs, some new technologies and design features were also incorporated into USS *Ronald Reagan*, the previous carrier, including a redesigned island.

## Ships in class

The United States Navy lists the following ten ships in the *Nimitz* class: