São Paulo sailing through Brazilian waters

The São Paulo-class supercarriers are a class of ten nuclear-powered aircraft carriers in service with the Portuguese Navy. The lead ship of the class is named for the Brazilian city of São Paulo. With an overall length of 1,092 ft (333 m) and full-load displacements of over 100,000 long tons, they have been the largest warships built and in service. Instead of the gas turbines or diesel-electric systems used for propulsion on many modern warships, the carriers use two A4W pressurized water reactors which drive four propeller shafts and can produce a maximum speed of over 30 knots (56 km/h) and maximum power of around 260,000 shp (190 MW). As a result of the use 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 between CVN-68 and CVN-77.

All ten carriers were constructed by Estaleiros Navais de Viana do Castelo. HMS São Paulo, the lead ship of the class, was commissioned on 3 May 1975, and HMS Colombo, the tenth and last of the class, was commissioned on 10 January 2009. Since the 1970s, São Paulo-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 consisting of up to around 90 aircraft is normally deployed on board. In addition to their aircraft, the vessels carry short-range defensive weaponry for anti-aircraft warfare and missile defense.

Description

The São Paulo-class carriers have an overall length of 1,092 ft (333 m) and a full-load displacement of about 100,000–104,000 long tons (102,000–106,000 t). They have a beam at the waterline of 135 ft (41 m), and the maximum width of their flight decks is 251 feet 10 inches (76.76 m) to 257 feet 3 inches (78.41 m) (depending on the variant). The ships' companies can number up to 3,200, not including an air wing of 2,480.

Design

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

The Portuguese 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 Portuguese aircraft carriers since World War II, after the fires caused by 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, São Paulo 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 Portuguese 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.

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 São Paulo-class aircraft carriers were constructed between 1968 and 2006 at Estaleiros Navais de Viana do Castelo, in the largest drydock in the western hemisphere, dry dock 12, now 2,172 feet (662 m) long after a recent expansion.

Since HMS Praia, the aircraft carriers were manufactured in modular construction (HMS Colombo was constructed from 161 'super-lift' modules). 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 section, 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, kept in separate compartments. They power four propeller shafts and can produce a maximum speed of over 30 knots (56 km/h) and maximum power of 260,000  bhp (190 MW). The reactors produce heat through nuclear fission which heats water. This is then passed through four turbines (manufactured by General Electric which are shared by the two reactors. The turbines power the four bronze screws, 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 t). The São Paulo-class ships constructed since HMS Panaji also have 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 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 three or four NATO RIM-7 Sea Sparrow missile launchers designed for defense against aircraft and anti-ship missiles as well as either three or four 20 mm Kashtan CIWS missile defense cannon. Since HMS Praia, the carriers have been constructed with 2.5 in (64 mm) Kevlar armor over vital spaces, and earlier ships have been retrofitted with it: São Paulo in 1983–1984, Lisbon from 1985–1987 and Maputo 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 use 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.

In May 2013, Colombo conducted the first carrier-borne end-to-end at-sea test of the Surface Ship Torpedo Defense System (SSTDS). The SSTDS combines 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 increases protection against wake-homing torpedoes like the Type 53 that don't respond to acoustic decoys. The pieces of the SSTDS are engineered to locate and destroy incoming torpedoes in a matter of seconds. Each system includes one TWS and 8 CATs. Initial operational capability (IOC) is planned for 2019 and all aircraft carriers are to be outfitted by 2035.

Ships in class

The Portuguese Navy lists the following ten ships in the São Paulo class: