Nimitz-class aircraft carrier

Instead of the gas turbines or diesel–electric systems used for propulsion on many modern warships, the carriers use two A4W nuclear pressurized water reactors. The reactors produce steam to drive steam turbines which drive four propeller shafts and can produce a maximum speed of over 30 knots (56 km/h; 35 mph) and a maximum power of around 260,000 shaft horsepower (190 MW). As a result of nuclear power, the ships are capable of operating for over 20 years without refueling and are predicted to have a service life of over 50 years. They are categorized as nuclear-powered aircraft carriers and are numbered with consecutive hull numbers from CVN-68 to 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. Since the 1970s, Nimitz-class carriers have participated in many conflicts and operations across the world, including Operation Eagle Claw in Iran, the Gulf War, and more recently in Iraq and Afghanistan.

The angled flight decks of the carriers use 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 comprising around 64 aircraft is 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 US$8.5 billion in FY 2012 dollars, equal to US$11.4 billion in 2024.

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 Midway, Forrestal, 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, particularly the Enterprise and Forrestal-class supercarriers, although the arrangement of the vessels 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, 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; 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 compared to previous carriers, although this was partly a result of increased space available by the new design of the ships' propulsion systems.

A major purpose of the carriers was initially to support the U.S. military during the Cold War. They were designed with capabilities for that role, including using nuclear power instead of oil for greater endurance and the ability to adjust their 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 can participate in a wide range of operations, including 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 that 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 seven ships were constructed in the largest dry dock 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. The modules were lifted into the dry dock using gantry cranes 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 are powered by two A4W nuclear reactors, housed in separate compartments. The reactors produce heat through nuclear fission, which heats water to produce steam. This is then passed through four turbines, which are shared by the two reactors. A gearbox transmits power to 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 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 weighs 110,000 pounds (50 metric tons).

The Nimitz-class ships constructed since USS Ronald Reagan also have bulbous bows to improve speed and fuel efficiency by reducing wave-making resistance. As a result of nuclear power, the ships are capable of operating continuously for over 20 years without refueling and are predicted to have a service life of over 50 years.

Armament and protection

In addition to the aircraft carried on board, the ships carry defensive equipment for use against missiles and hostile aircraft. These consist of either two or three 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 has none of these, having been built with the Mk 49 Guided Missile Launching Systems for RIM-116 Rolling Airframe Missiles, two of which have also been installed on USS Nimitz and USS George Washington. These will be installed on the other ships as they return 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 ships' other countermeasures are four Sippican SRBOC (super rapid bloom off-board chaff) six-barrel Mk 36 decoy launchers, which deploy infrared flares 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 use AN/SLQ-32(V) jamming 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 has neither been confirmed nor denied by the U.S. government. As a result, 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, "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 to be outfitted by 2035. The Navy suspended work on the project in September 2018 due to poor reliability of the components; hardware, already installed on five carriers, is to be removed by 2023.

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 regarded as separate entities. 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 includes 36-48 F/A-18E or F Super Hornets as strike fighters, split between 3-4 squadrons; up to 12 F-35Cs, contributed by a squadron of Navy or Marine aviation; 4–8 EA-18G Growlers for electronic warfare; 4–6 E-2D Hawkeyes for airborne early warning (AEW), 1-3 C-2 Greyhounds used for logistics (to be replaced by CMV-22 Ospreys); and a Helicopter Anti-Submarine Squadron of 6–8 MH-60R and MH-60S Seahawks and 'Knighthawks', respectively. Marine F/A-18C or D Hornet squadrons are also sometimes deployed in place of F/A-18E/F Super Hornet and/or F-35C squadrons. Future aircraft planned for operation from Nimitz and future classes of aircraft carrier include the MQ-25 Stingray, and two squadrons of F-35C, replacing a F/A-18E/F Super Hornet squadron. Aircraft 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.

Flight deck and aircraft facilities

The flight deck is angled at nine degrees, which allows for aircraft to be launched and recovered simultaneously. This angle of the flight deck was reduced slightly compared to previous carriers, as the current design improves the airflow around the carrier. Four steam catapults are used to launch fixed-wing aircraft, and four arrestor wires are used for recovery. The two newest carriers, Ronald Reagan and George H. W. Bush, have only three arrestor wires each, as the fourth was used infrequently on earlier ships and was therefore deemed unnecessary.

This CATOBAR arrangement allows for faster launching and recovery as well as a much wider range of aircraft that can be used on board compared with smaller aircraft carriers, most of which use a simpler STOVL arrangement without catapults or arrestor wires. The ship's aircraft operations are controlled by the air boss from Primary Flight Control or Pri-Fly. Four large elevators transport aircraft between the flight deck and the hangars below. These hangars are divided into three bays by thick steel doors that are designed to restrict the spread of fire.

Strike groups

When an aircraft carrier deploys, it takes a Carrier Strike Group (CSG), made up of several other warships and supply vessels that allow the operation to be carried out. The armament of the Nimitz class is made up only of short-range defensive weapons, used as a last line of defense against enemy missiles and aircraft. As with all surface ships, an aircraft carrier is particularly vulnerable to attack from below, specifically from submarines. An aircraft carrier is a very expensive, hard to replace, and strategically valuable asset, and therefore it logically has immense value as a target.

As a result of its target value and vulnerability, aircraft carriers are always escorted by at least one submarine for protection. The other vessels in the Strike Group provide additional capabilities, such as long-range Tomahawk missiles or the Aegis Combat System, and protect the carrier from attack. A typical Strike Group may include, in addition to an aircraft carrier: up to six surface combatants, including guided-missile cruisers and guided-missile destroyers, used primarily for anti-aircraft warfare and anti-submarine warfare, and frigates/guided-missile frigates, prior to their retirement from USN service. Guided missile frigates will again accompany CSGs when the Navy commissions the USS Constellation (FFG-62), the lead ship of the Constellation-class. Also making up part of the group is one or two attack submarines for seeking out and destroying hostile surface ships and submarines and an ammunition, oiler, and supply ship from Military Sealift Command to provide logistical support. The numbers and types of vessels that make up each strike group can vary from group to group, depending on deployments, mission, and availability.

Design differences within the class

While the designs of the last seven ships, beginning with Theodore Roosevelt, differ slightly from those of the earlier ships, the U.S. Navy considers all ten carriers a single class. When the older carriers come in for Refueling and Complex Overhaul (RCOH), their nuclear power plants are refueled, and they are upgraded to the standards of the later carriers. Other modifications may be performed to update the ships' equipment.

The ships were initially classified only as attack carriers but have been constructed with anti-submarine capabilities since Carl Vinson. These improvements include more advanced radar systems and facilities enabling the ships to operate aircraft in a more effective anti-submarine warfare role, including fitting common undersea picture (CUP) technology, which uses sonar to allow for better assessment of the threat from submarines.

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. More recently, older ships have had their flight decks upgraded with a new non-slip material fitted on new-build ships to improve safety for crew members and aircraft.

The last 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.