By the middle of World War II, carrier-borne aircraft become so effective that the aircraft carrier was clearly replacing the battleship as the core of the modern navy. Since the war, the development of jet aircraft and nuclear-powered ship propulsion has magnified the range and speed of operations, but it has not altered the central role of the carrier.
At the same time, though, a new equalizer has been developed: the antiship guided missile. This weapon, which can be mounted onto the smallest surface vessels as well as aircraft and submarines, is especially dangerous to aircraft carriers because it can be launched outside antiaircraft range and, being unmanned, cannot be distracted easily by defensive fire. The main defense now is to provide the fleet with its own guided missiles capable of destroying either the missile or its launching platform.
Propulsion
The diesel engine, adapted to warships even before World War II, has remained in use in the navies of the world, as have steam turbines. But steam propulsion reached its ultimate development with the use of the energy released by nuclear fission to heat the boilers of steam turbines. In addition, the gas turbine, a turbine in which the combustion of fuel generates a stream of gases that turns the rotor, has become available for ship propulsion.
Nuclear power
Nuclear power was proposed for ships, particularly submarines, in 1945, and by 1955 the United States had a nuclear submarine, USS Nautilus, in service. Other navies followed suit, so that within 20 years Britain, the Soviet Union, France, and China all operated nuclear submarines. In the 1950s the United States also developed nuclear power plants for surface ships, subsequently installing them aboard aircraft carriers and their escorts. The Soviet Union and France followed with more limited programs in the 1970s and ’80s.
For a surface ship, the advantage of nuclear power is effectively infinite range at high speed. The disadvantage is the high cost, which limits such power to a few valuable ships built by the wealthiest powers—in most cases, the United States.
Gas turbines
Gas turbines share with internal combustion piston engines the great virtues of quick starting and stopping as well as relatively simple operation. They are also quite reliable. Their main defect is that they are efficient only over a relatively narrow speed range. For this reason, the first gas turbine warships employed combination power plants, such as combined steam and gas turbine (COSAG) or combined diesel and gas turbine (CODAG). Using such a plant, a relatively small ship, such as a frigate, could achieve much higher speed than with a conventional steam turbine. The next step was to combine two gas turbines, one sized for cruising and the other for high speed. Such an arrangement might be either combined gas and gas (COGAG), with both plants able to operate together, or combined gas or gas (COGOG), with only one plant being used at a time.
Systems employing the gas turbine have proved useful in smaller escort ships such as destroyers and frigates, although they have also been installed in cruiser-sized vessels. A related system, called combined diesel, electric, and gas turbine (CODLAG), is especially valuable in submarine warfare. In order to minimize engine noise, which may interfere with sonar sensors, diesel generators power electric motors, which in turn drive the ship’s propellers. For higher speeds, electricity is supplemented or replaced by gas turbines.
Armour
The role of armour has greatly declined since 1945 because aircraft, the greatest threat to warships, now carry guided missiles and bombs capable of penetrating the thickest deck armour that any viable ship can accommodate. At the same time, warships’ new missile weaponry has occupied much more space than did the earlier guns, shells, and powder. Modern weapon systems also require room for computers and radars and for their operators. To cover such spaces with anything but the lightest plating would add enormous weight and thus require very large and expensive hulls. The high cost of protection (in ship size as well as money) is a major reason for the abandonment of heavy, extensive armour in the guided-missile era.
Armour has not been abandoned altogether, however. Thin armour, for example, can protect aircraft and missiles from the steel splinters of exploding warheads and thus can keep a ship hit elsewhere from being destroyed by a huge explosion of jet fuel or its own missiles. For this reason most modern warships have adopted thin (about 25- or 50-mm, or one- or two-inch) splinter protection around their missile magazines.
Aircraft carriers, at least in the U.S. Navy, have retained armoured flight decks, though in their case the armour provides structural strength as well as limited protection.
Aircraft carriers
Since World War II the heavy attack aircraft carrier has developed three roles: to deliver air strikes (both conventional and nuclear) against sea and shore targets; to provide a long-range air-defense umbrella for other ships; and to support antisubmarine operations (leaving it to other ships actually to destroy the submarines). In order to carry out these roles, jet carriers have become so huge that only a first-rate power can afford to build and operate them. Today only the United States and France operate full-scale carriers (although the 38,000-ton French Charles de Gaulle is closer in size to the carriers of the immediate post-World War II period than to the 80,000-ton, 1,000-foot [300-metre] behemoths built by the United States since the 1970s). The Soviet Union considered building large carriers, but the idea was abandoned by Russia after the collapse of the Soviet system in 1991.
Navies that cannot afford the large carrier have divided its three roles among escort ships and light aircraft carriers. The light aircraft carriers have been given the role of antisubmarine warfare, along with limited ground-attack and air-protection capabilities.
