Flight deck
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Image:USS Stennis HMS Illustrious.jpg Image:Stennis RudderSwing3.JPG
The flight deck of an aircraft carrier is the surface from which its aircraft take off and land, essentially a miniature airfield at sea.
In early carriers, the flight deck was a sort of long flat superstructure built above the rest of the ship; this was both a relatively simple addition to make, and offered a little extra room for airplanes strugging to gain altitude after taking off. These decks were made of wood and would occasionally include a small ramp at one end to aid in take-off. Ships of this type were still being built into the late 40s, in the form of the US Navy's Essex and Ticonderoga class carriers. The earliest carriers were converted merchant ships, fleet colliers or cruisers, especially battlecruisers that otherwise would have had to have been discarded under the Washington and London Treaties. Because the military effectiveness of aircraft carriers was then unknown, these ships were typically equipped with cruiser-grade guns to aid in their defense if surprised by enemy warships. These guns were generally removed during the early days of World War II and replaced with a smaller battery of 5" anti-aircraft guns, as carrier doctrine developed the "task force" (later called "battle group") model, where the carrier's defense against surface ships would be a combination of escorting warships and its own aircraft.
Landing an aircraft on an aircraft carrier was made possible through the use of arresting cables installed on the flight deck and a tailhook installed on the aircraft. Early carriers had a very large number of arresting cables or "wires". Current U.S. Navy carriers have three or four steel cables stretched across the deck at 20-foot (6 meter) intervals which bring a plane, traveling at 150 miles per hour (240 kilometers per hour), to a complete stop in about 320 feet (98 meters). The cables are set to stop each aircraft at the same place on the deck, regardless of the size or weight of the plane.
Early carriers were vulnerable to fire on deck, particularly during refueling. After refueling, fuel lines in the deck would be purged with exhaust gasses to reduce the vulnerability to fire.
Later the flight deck was designed into the carrier hull, becoming a structural element (a move necessitated by the ever-increasing size of the ships, from the 13,000 ton USS Langley (CV-1) in 1922 to over a hundred thousand tons in the latest Nimitz-class carriers), and later still, were made of steel. Aircraft are given extra speed to assist take-offs by catapults.
Another innovation was the angled flight deck, in which the aft part of the deck is widened and a separate runway positioned at an angle. This increases the safety of landings by allowing a plane that "bolters", or misses the arresting gear, to become airborne again without concern for aircraft parked forward. The angle deck also allows the ship to conduct concurrent launch and recovery operations.
A more recent innovation is the "ski jump" deck, which is curved upwards at its forward end, helping aircraft clear the waves more quickly.
On smaller Navy and naval ships which do not have aviation as a primary mission, the landing area for helicopters and other VTOL aircraft is also referred to as the flight deck. These ships are often referred to as "aviation capable ships" (this is the official U.S. Navy term).