An aircraft carrier is a warship designed to support and operate aircraft, engage in attacks on targets afloat or ashore, and engage in sustained operations in support of other forces. Smaller carriers may only be able to operate short takeoff and vertical landing (SVTOL) aircraft, as well as vertical takeoff and landing (VTOL) helicopters and tilt-rotor aircraft. The largest and most capable carriers have catapults that can, in seconds, accelerate carrier-capable conventional takeoff and landing (CTOL) small and medium aircraft to flying speed; they also have a system of arresting wires, which allows a high-performance aircraft to be brought to a stop in seconds. This technique is called Catapult Assisted Take Off But Arrested Recovery (CATOBAR); the catapult and arresting systems are major components, but certainly not the only ones involved. At present, only the United States, France, and Brazil operate CATOBAR carriers. Two 65,000 ton British Queen Elizabeth-class carriers under construction, as well as possible future French construction that would use the British design, will start as STOVL, but are intended to be convertible to CATOBAR.
Whenever a nation, with power projection capability, faces a crisis, among the first questions asked by its leaders is "Where are the carriers?" Other than those exclusively for amphibious or antisubmarine operations, the worldwide navies with carriers in operation or under construction include:
For amphibious warfare, several nations also have STOVL or VTOL ships that are not called "carriers", although this is often for reasons of domestic, or even interservice, politics. U.S. Wasp-class amphibious assault ships are 40,000 ton VTOL vessels, compared to the Brazilian (ex-French) 32,000 CATOBAR carrier, São Paulo. HMS Ocean (1995), is sometimes called an amphibious assault ship but, at 21,500 tons, is designated a Landing Platform Helicopter.
In U.S. carrier operations, the general rule is that for a routine tempo of operations, there need to be three carriers for each one deployed in operational areas. Carriers need periodic shipyard maintenance, sometimes major overhauls of the Service Life Extension Program (SLEP) that add years of operational use, but may take several years. As new crewmembers come aboard, and new equipment and techniques are introduced, the carriers need time to work them into a team. Assembling a six-carrier presence, as in the Gulf War, is an immense logistical and operational challenge.
Modern carrier task force operations
Carriers never operate alone, but as the center of a group of escort and support vessels. In the Second World War, they operated at the center of concentric rings of cruisers and battleships that were there as massive anti-aircraft artillery platforms. Rings of destroyers and other light ships formed outer screens against submarines, and to give early warning of air attack.
The commanding officer of the task force usually makes the carrier his or her flagship, as it typically has the most space for a group staff. Tactical anti-air warfare and anti-submarine warfare officers may be aboard escorts, but typically carriers, large amphibious ships, and, if a country uses them, purpose-built command ships can handle a large staff.
Only the United States (primarily Nimitz-class) and France (single Charles de Gaulle-class; possible future construction) operate large carriers, although the United Kingdom pioneered many large carrier techniques and has started construction of two 65,000 carriers of the Queen Elizabeth class. If France builds additional carriers, they will be based on the new British design.
Carrier strike group
Minimally, a modern carrier strike group (CSG) is made up of a CATOBAR (usually) carrier, one or more cruisers, two or more destroyers, one or more attack submarines, and a supply ship. The submarine(s) scout ahead, as the most efficient anti-submarine warfare platforms. Next come the destroyers, as multipurpose screens. The cruiser both directs anti-air warfare, and is a major surface-to-air missile (SAM) launcher. Both the cruisers and destroyers can launch cruise missiles as well as launch anti-air and anti-submarine weapons; the carrier's own aircraft are a major defensive capability. In U.S. terminology, the carrier task group proper consists of the carrier, replenishment ship, and a subset of the escort; it becomes a strike group with a full set of escorts.
Amphibious Ready Group
The U.S. and U.K. also form amphibious ready groups around a set of amphibious warfare ships, at least one of which is a STOVL or VTOL vessel that carries helicopters and STVOL fighter aircraft. In U.S. doctrine, the ARG, with a full set of escorts, can operate independently as an expeditionary strike group, or in company with a CSG. If the group is large enough to need a flag officer, the largest aicraft-capable amphibious ship will usually be the flagship.
The ARG carries a (U.K.) Royal Marine Commando or (U.S.) Marine Amphibious Unit (MEU). In the Falklands War, U.K. forces, lacking a full CTOL carrier, used a formation that employed two STOVL carriers both for defensive counter-air and close air support with STOVL aircraft, as well as a large complement of escorts, and an amphibious group of considerable size, able to lift part of a division.
More as a Second World War than modern doctrine, small aircraft carriers, generally converted from commercial hulls and without the speed or survivability of fleet carriers, operated in a variety of roles, especially Atlantic convoy support, either close-in or as a standoff Support Group. They embarked STOL fixed-wing aircraft.
The escort carriers also served as aircraft ferries, both for replacement of naval aircraft, primarily in the Pacific, and to deliver Army Air Force planes ashore.
Initial tests involved not purpose-built carriers or even full flight decks, but experiments from improvised platforms on cruisers. The first takeoff from a ship took place on 14 November 1910, by Eugene Ely, a civilian test pilot for the U.S. Navy. On this occasion, he did not return to the improvised carrier, the scout cruiser USS Birmingham (CL-2), but on 18 January 1911, he did take off and return to a flight platform on the armored cruiser USS Pennsylvania. 
Britain adapted the large light cruiser HMS Furious in 1917, to what would be the first operational aircraft carrier.
In the U.S. Navy, the first conversion to a carrier was the USS Langley (CV-1). She was converted from a collier. Commissioned in 1922 as a warship, she was still seen as experimental. Her catapults, for example, used a flywheel power source quickly found to be impractical. She lacked the island structure found necessary to have an unobstructed view of the flight deck.
USS Ranger (CV-4) was laid down as a carrier, but proved to be too small for most operations. Although converted and small purpose-built carriers served in combat, the first reasonably successful purpose-built U.S. carriers were of the Essex-class (WWII), which served into the Korean War, and, with modifications and in more supporting roles, into the Cold War.
Historic carrier operations
Carriers have dominated naval warfare since the Second World War, but most of their operations have been against shore targets, surface ships without aircraft support, and submarines. The Battle of Pearl Harbor, of course, brought the U.S. into the war. That raid was launched from six Japanese carriers; at-sea U.S. carriers tried to find and engage them, although the Japanese force was then much superior and would likely have been disastrous for the U.S.
U.S. forces responded with the Doolittle Raid, a takeoff-only carrier attack like the Torndern Raid.
There have only been five battles between carrier forces, the motivation of the title, the Sixth Battle, of Barrett Tillman's novel about a future carrier battle. The five battles were:
- Battle of the Coral Sea
- Battle of Midway
- Battle of the Eastern Solomons
- Battle of the Santa Cruz Islands
- Battle of the Philippine Sea
In 1982, there was the possibility of a carrier battle between Argentinian and British forces in the Falklands War, but the Argentinian carrier returned to port. Argentine Navy aircraft, however, did operate from land bases.
Developing the people
Aircraft take off and land from the flight deck, which is one of the most dangerous places outside an intense battlefield. On U.S. ships, every crew specialty is indicated by color-coded jackets and helmets, with constant visual monitoring and loud, immediate calls to anyone out of their assigned area.
It took decades to work out the technologies of modern carrier operations, which changed dramatically with the introduction of jet aircraft following the Second World War. Just as important as the launching and landing technology are the disciplines of operations, which took as long to work out. A nation may build or buy its first carrier, but it will take longer to train the carrier crew and aviators, and build the infrastructure to pass on the hard-won lessons.
While Japan started WWII with a group of magnificently trained aviators, they made a terrible mistake by not rotating them back ashore to train new pilots, think about improved doctrine, and prepare for the next level of responsibility. Not only did Japan gradually lose very good people in air combat, the losses of skilled personnel, at the Battle of Midway may have been even more disastrous than the four sunken carriers. The Battle of the Philippine Sea, also known as the "Marianas Turkey Shoot", destroyed what was left of a critical mass of aircrew. In contrast, the U.S. had a constant rotation cycle, where new pilots served a first combat tour, came back ashore and became a flight instructor, and then rotated back as a flight or squadron leader. After cruises in leadership, they again went back to teach and think, and to qualify as department heads, and eventually air group commanders, carrier captains, and, later, carrier task force admirals.
CTOL and STOVL carrier technology
A modern CTOL carrier is characterized by several key technologies:
- Angled deck
- Electro-optical landing system
- Advanced catapult (now steam, but moving toward electromagnetic)
In practice, carriers are also flagships and need extensive communications, electronics, and electrical power. Given the fire and explosion hazard of the air wing and its ammunition, they need extensive protective and damage control arrangements.
The very first experiments with launching seaplanes used catapults, but, with the first true carriers, the propeller-driven aircraft were small and light enough to be able to reach takeoff speed under their own power. Carriers would also turn into the wind for flight operations, and steam at maximum speed, so the aircraft had the benefit of the ship's momentum and of a wind providing lift. As in the Doolittle raid, it was easier to take off than land.
As carrier aircraft grew heavier, their own engines simply did not have the power to develop adequate speed by running down the deck. While a few experiments with rocket boosters had specialized applications, the model had to change to using immensely powerful catapults to bring the aircraft to flying speed within seconds. Originally, catapults were flywheel, and then hydraulically powered, but some disastrous accidents (e.g., USS Bennington (CV-20) in 1954), and inherent limitations of the power of hydraulics, led to the current generation of steam-driven catapults. The steam comes from the main engines of the carrier.
Catapult-equipped carriers are the standard in the U.S. Navy and France. Electromagnetic catapults are under active development and may significantly increase capabilities, but they also present a set of unique challenges.
Several countries, including India, Russia, Spain and the U.K., do not have catapults, but do have a "ski jump" ramp that can greatly increase the takeoff load capability of a STOVL aircraft. British and possibly French carriers in design and construction may have an unusual combination of ski jump and angled deck, the latter more typical of catapult-equipped CTOL carriers.
On the earliest carriers, the slow aircraft would land as if they were landing on a short conventional airstrip. Very quickly, it became obvious that weather and the carrier's course and speed very much influenced the flight path for approach. Beyond the general path, the reality was that as opposed to a land-based airstrip, the carrier deck was moving, often in a way not visible to the pilot in the final moments of landing.
It is essential to realize that the early CTOL carriers had a straight deck. As will be seen, introduction of an angled deck greatly simplified air operations.
+++++++++++++++++++++++++++++ |Stern |.... |Parked aircraft | | | | | V |Barricade (when used) |... (area used for handling | just-landed aircraft | |----- Arresting wire 4 |----- Arresting wire 3 |----- Arresting wire 2 |----- Arresting wire 1 | |Front of ramp ++++++++++++++++++++++++++++++ V bow
As carriers grew in size, they tended to have just-landed, or ready-for-takeoff, aircraft parked on the flight deck. It was all too easy to have a pilot, who landed too far down the then-straight deck, to crash into the parked aircraft at the far end. It was equally easy to try to land too early, and crash into the carrier's bow or the forward projection of the flight deck; such a short landing is called a ramp strike and is often fatal.
The first barricades were strong nets positioned in front of the parked aircraft, and was a protective system rather than a last-resort landing method. Later barricades could catch an aircraft and stop it, usually with damage but generally with crew survival. Barricades became less necessary with the angled deck (see below)
Arresting wire systems
The first purpose-built carrier systems used the combination of a number of arresting wires across the intended landing area. Carrier-capable aircraft either would lower, or have in a permanently lowered position, an extremely strong tailhook. As the aircraft sank toward the deck, the tailhook, if all went well, would engage one of the arresting wires, and bring the aircraft to a sudden stop.
The most common arrangement uses four landing wires, with #3 the preferred target.
As aircraft grew heavier, being stopped by a stiff wire could cause too intense a deceleration, possibly ripping the hook out of the aircraft but not stopping flight. Overstressed cables could snap, and whip around the deck with force sufficient to cut crewmen in half.
Eventually, the arresting wires acquired adjustable tensioning mechanisms and takeup spools, so that when an aircraft firmly engaged the wire, the wire would move a calculated distance forward, reducing the shock of deceleration.
Flexibility in the arresting wire, however, did not deal with the very real situation where an aircraft missed all the wires, but had slowed to a speed that committed it to landing somewhere on the deck. The first several generations of carrier aircraft did not have engines that could accelerate fast enough for an emergency "go-around", although the combination of the angled deck and primarily jet engines eventually provided a solution.
It must never be forgotten, however, that an arrested carrier landing is a controlled crash, and one of the most dangerous operations in aviation. Physiological monitoring of pilots consistently showed higher stress levels during night carrier landings than in active combat, even in a dogfight or under heavy antiaircraft fire.
When considering the landing path, (graphic needed), there comes a point when the pilot's view of the landing area is obscured by the nose. This is true, to a lesser extent, in landings on airfields ashore, but those landings do not involve the critical distances needed to engage the arresting wire.
The first solution was to have use Landing Signal Officers, who were experienced pilots, on the carrier deck near the landing path, who could see the aircraft and the deck, and signal the aircraft if it needed to be higher, lower, more left or right, faster or slower, and when it needed to abort the landing.
Just as pilots inherently dislike ignoring their own eyes and trusting their all-weather flying instruments, the idea of substituting another pilot's judgmnent for final landing was not popular -- but it was, until much more advanced technology emerged, the only viable solution.
- Landing signal officer ("paddles")
- Optical landing systems
A typical Carrier Air Wing is made up of:
- 4 F-18 Hornet or F-18 Super Hornet multirole squadrons, with partial replacement of the Hornets by the future F-35C Lightning II
- 1 electronics warfare detachment, with EA-6B Prowlers to be replaced by EF-18 Growlers
- 1 E-2 Hawkeye airborne early warning squadron
- 1 helicopter squadron, evolving but eventually to be either all MH-60R Seahawks or a mixture of MH-60R and MH-60S Knighthawks
U.S. amphibious vessels can carry the AV-8 Harrier II STVOL fighter, MV-22 Osprey VTOL tilt-rotor aircraft, as well CH-46, CH-53 and AH-1 Cobra helicopters. Since their primary emphasis is on helicopters, they do not have "ski jump" facilities to optimize STVOL takeoff.
Joint developments with U.S.
Given the level of experience needed to design effective carrier-capable aircraft, many modern carrier operators use U.S. CTOL aircraft. The widely used STOVL Harrier series were developed by the United Kingdom, and the next-generation Joint Strike Fighter carrier and STOVL versions are US-British collaborations. Britain's new Ocean-class carriers will use JSF; the carriers will initially be "ski jump" although convertible to CATOBAR.
Italy and Spain will probably use the STOVL variant.
Various European countries and cooperatives are exploring carrier aircraft modifications. France had built past successful designs such as the Super Etendard attack plane, and has been working on a navalized version of the modern Rafale. Consortia are looking at navalized Eurofighter designs.
- Eugene Ely's Flight from USS Birmingham, 14 November 1910, U.S. Naval Historical Center
- The "Big E" earned 20 battle stars for World War II service, making her the most decorated ship in U.S. history. SHe was also the only aircraft carrier in operation at the beginning of the conflict still in service at war's end.