Aircraft carriers can be split into two groups depending on their shape - straight-deck carriers, and angled-deck carriers. Most modern carriers are angled-deck to allow simultaneous take-offs and landings.
The hull of the ship is made up of extremely strong steel plates, measuring several inches thick. This heavy body is highly effective protection against fire and battle damage. The ship's structural support largely comes from three horizontal structures extending across the entire hull: the keel, the flight deck and the hangar deck.
The hull portion below the water line is rounded and relatively narrow, while the section above water flares out to form the wide flight-deck space. The lower section of the ship has a double bottom, made out of two layers of steel plating: the bottom plating of the ship and another layer above it, separated by a gap. The double bottom provides extra protection from torpedoes or accidents at sea.
- Catapult-Assisted Take-Off but Arrested Recovery (CATOBAR): These carriers generally large, heavy, well-armed aircraft and strike fighters, although smaller CATOBAR carriers may have other limitations (weight capacity of aircraft elevator, and so on). Three nations currently operate carriers of this type: ten by the United States, and one each by France and Brazil for a total of twelve in service.
- Short Take-Off but Arrested Recovery (STOBAR): These carriers are generally limited to carrying lighter aircraft with more limited payloads. STOBAR carrier-based aircraft, such as the Sukhoi Su-33 and future Mikoyan MiG-29K of the Admiral Kuznetsov are often geared primarily towards air superiority and fleet defense roles rather than strike/power projection tasks, which require heavier payloads (bombs and air-to-ground missiles). Currently, Russia, China, and India possess commissioned carriers of this type.
- Short Take-off Vertical-landing (STOVL): Limited to carrying STOVL aircraft. STOVL aircraft, such as the Harrier Jump Jet family and Yakovlev Yak-38 generally have very limited payloads, lower performance, and high fuel consumption when compared to conventional fixed-wing aircraft; however, a new generation of STOVL aircraft, currently consisting of the F-35B, has much improved performance. This type of aircraft carrier is in service with one for India and two for Italy. Spain also operates one amphibious assault ship as a STOVL aircraft carrier for four ships total in active carrier service; Thailand has one active STOVL carrier but it no longer has any operational STOVL aircraft in inventory. Some also count the nine US amphibious assault ships in their secondary light carrier role, boosting the overall total to fourteen.
- Helicopter Carrier: Helicopter carriers have a similar appearance to other aircraft carriers and can often support aircraft. Some support a ski jump ramp allowing for STOVL operations or may have an unused ski jump installed before retirement of STOVL aircraft and re-purposing, in the past, conventional carriers were converted and identified as commando carriers. Some helicopter carriers with a resistant flight surface can operate VTOL jets. Currently, the majority of helicopter carriers, but not all, are classified as amphibious assault ships, tasked with landing and supporting ground forces on enemy territory. The US has nine of this type, France three, the JMSDF two, the UK one, the Republic of Korea one and Spain one. The US and Spain's amphibious assault ships operate STOVL jets in normal deployment.