Aircraft Carrier Structure
Carriers are large and long ships, although there is a high degree of variation depending on their intended role and aircraft complement. The size of the carrier has varied over history and among navies, to cater to the various roles that global climates have demanded from naval aviation.
Regardless of size, the ship itself must house their complement of aircraft, with space for launching, storing, and maintaining them. Space is also required for the large crew, supplies (food, munitions, fuel, engineering parts), and propulsion. US supercarriers are notable for having nuclear reactors powering their systems and propulsion. This makes the carrier reasonably tall.
The top of the carrier is the flight deck, where aircraft are launched and recovered. On the starboard side of this is the island, where air-traffic control and the bridge are located.
The constraints of constructing a flight deck affect the role of a given carrier strongly, as they influence the weight, type, and configuration of the aircraft that may be launched. For example, assisted launch mechanisms are used primarily for heavy aircraft, especially those loaded with air-to-ground weapons. CATOBAR is most commonly used on USN supercarriers as it allows the deployment of heavy jets with a full loadout, especially on ground-attack missions. STOVL is used by other navies because it is cheaper to operate and still provides good deployment capability for fighter aircraft.
Due to the busy nature of the flight deck, only 20 or so aircraft may be on it at any one time. A hangar storage several decks below the flight deck is where most aircraft are kept, and aircraft are taken from the lower storage decks to the flight deck through the use of an elevator. The hangar is usually quite large and can take up several decks of vertical space.
Munitions are commonly stored on the lower decks because they are highly explosive should the compartment they are in be breached. Usually, this is below the water line so that the area can be flooded in case of emergency.