Flight deck
- For the flight deck of an aircraft, see cockpit
The flight deck of an aircraft carrier is the surface from which its aircraft take off and land, essentially a miniature airfield at sea. On smaller 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. The official U.S. Navy term for these vessels is "aviation capable ships".
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Evolution
Early flight decks
The first flight decks were inclined wooden ramps built over the forecastle of naval warships. Eugene Ely made the first airplane take-off from a warship from USS Birmingham on 14 November 1910 and on 4 May 1912, Commander Charles Samson became the first man to take off from a ship which was underway when he flew his Shorts S27 off of HMS Hibernia, which was steaming at 10.5 knots. Because the take-off speed of early aircraft was so low, it was possible for an aircraft to make a very short take off when the launching ship was steaming into the wind. Later, removable "flying-off platforms" appeared on the gun turrets of battleships and battlecruisers, allowing aircraft to be flown off for scouting purposes, although there was no chance of recovery.
On 3 August 1917, while performing trials, Squadron Commander Edwin Dunning landed a Sopwith Pup successfully on board the flying-off platform of HMS Furious, becoming the first person to land an aircraft on a moving ship. However, on his second attempt, a tyre burst as he attempted to land, causing the aircraft to go over the side, killing him (gaining the dubious distinction of being the first person to die in an aircraft carrier landing accident). The landing arrangements on Furious were highly unsatisfactory, however; in order to land, aircraft had to manoeuvre around the superstructure. Furious was therefore returned to dockyard hands have a 300 foot (91 m) deck added aft for landing, on top of a new hangar. However, the central superstructure remained, and turbulence caused by this badly affected the landing deck.
Full length decks
The first aircraft carrier that began to show the configuration of the modern vessel was the converted liner HMS Argus, which had a large flat wooden deck added over the entire length of the hull, giving a combined landing and take-off deck unobstructed by superstructure turbulence. Because of her unobstructed flight deck, Argus had no fixed conning superstructure and no funnel. Rather, exhaust gasses were trunked down the side of the ship and ejected under the fantail of the flight deck (which, despite arrangements to disperse the gasses, gave an unwelcome "lift" to aircraft immediately prior to landing). The lack of a command position and funnel was unsatisfactory, and Argus was used to experiment with various ideas to remedy the solution. A photograph in 1917 shows her with a canvas mock-up of a starboard "island" superstructure and funnel. This was to starboard as the rotary engines of early aircraft caused a force to the left, meaning an aircraft naturally yawed to port on take-off, therefore it was desirable that they turned away from the fixed superstructure. This became the typical aircraft carrier arrangement and was used in the next British carriers, HMS Hermes and Eagle.
After World War I, many battlecruisers that otherwise would have had to have been discarded under the Washington Naval Treaty were converted to carriers on the above lines. Being large, and fast, they were perfectly suited to this role; the heavy armouring and scantlings and low speed of the converted battleship Eagle served to be something of a handicap. Because the military effectiveness of aircraft carriers was then unknown, early ships were typically equipped with cruiser-sized guns to aid in their defence if surprised by enemy warships. These guns were generally removed during World War II and substituted for anti-aircraft guns, as carrier doctrine developed the "task force" (later called "battle group") model, where the carrier's defence against surface ships would be a combination of escorting warships and its own aircraft.
In ships of this configuration, the hangar deck was the strength deck, and part of the hull, and the hangar and wooden flight deck were considered to be part of the superstructure. Such ships were still being built into the late 40s, classic examples being the US Navy's Essex and Ticonderoga class carriers. However, in 1936, the Royal Navy began construction of the Illustrious class "armoured carriers". In these ships, the flight deck was now the strength deck, an integral part of the hull, and was heavily armoured to protect the ship and her air complement. Although the armoured carrier concept in this form remained something of a dead end, the flight deck as the strength deck was adopted for later construction. This was 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.
An important British innovation, introduced in the unarmored HMS Ark Royal, was the "hurricane bow", where the bow was sealed up to the flight deck level, making the hangar deck much drier, especially in heavy weather. This feature would be incorporated into later American carriers. It proved to be by far the most useful configuration for the bow of the ship among the many that were tried, including a second flying-off deck and an antiaircraft battery (the most common American configuration during World War II).
Armored decks
The carriers that were built with armored decks fall into two distinct types - those with the armor at flight deck level protecting everything below (typified by British ships) and those that had the armor between the hangar and the rest of the ship as in American and Japanese carriers. The two approaches had different effects on the ships though US carriers of World War II had similar thicknesses of armor as their British counterparts.
In ships that carried their armor at the hangar deck level, the flight deck and anything above it was superstructure. This allowed for larger, open-sided hangar bays (improving ventilation) and the installation of deck-edge elevators. Carriers with wooden flight decks were vulnerable to fire on deck, particularly during refuelling. After refuelling, fuel lines in the deck would be purged with exhaust gasses to reduce the vulnerability to fire. The armoured carrier concept had a sealed hangar with excellent fire-prevention arrangements, but suffered from an inability to run-up aircraft engines under cover; any work requiring engines to be running had to be carried out on the flight deck.
The Royal Navy's armoured carriers carried their armor at the flight deck level. Within the confines of the ship design this resulted in lower hangar heights and a detrimental effect on the number and size of the aircraft that could be carried. No British carrier other than the early HMS Argus had a hangar to match the 20 ft in hangar height of the American Lexington class or 17'6" hangars of the Yorktown and Wasp. Indeed, with her capacious hangar, Argus was the only British aircraft carrier of the Second World War capable of striking down aircraft without folded wings. The operation of larger late-war fighters like the Blackburn Firebrand and F8F Bearcat and ever larger post-war jets would prove problematic, compounded by the fact that there were fewer and smaller elevators, as these had to be cut into the armor and armored themselves.
Carrying the armor at the flight deck level would protect the hangar deck and the aircraft stored there from light bombs (the Illustrious class was protected, for example, against only 200 pound bombs and were very poorly protected against the heavy 500 pound bombs that became common during the war) that struck the deck. Carrying it lower meant that if a bomb struck the flight deck there was more likelihood of it penetrating to the hangar deck and causing damage there, but that the armor would still protect the rest of the ship including the engine spaces and fuel storage (the flight deck also tended to initiate heavy bombs, keeping the explosion out of the hull proper). The lower deck armor improved stability (by putting the heavy weight of the armor lower in the ship) and damage control (by moving the large void space represented by the hangar out of the hull and into the superstructure).
The differences in doctrine were largely driven by the different circumstances of the two services. The United States Navy had its own aircraft procurement budget and procedures, independent of the Army Air Corps, and thus had plenty of aircraft and envisioned deck parks and massive strikes, keeping damage away by keeping the enemy on the defensive, or by defensively intercepting enemy aircraft before they could attack the carriers on their own. The Royal Navy's Fleet Air Arm was constrained by the Royal Air Force and the inter-war emphasis on developing a strategic bomber force. At the outset of the war it had fewer, smaller and older planes and its carriers had to be built under the assumption that they would take damage from operating under the umbrella of land-based enemy air forces in Europe (though the RN's eyes roved as much over the vast spaces of the Indian and Pacific Oceans and never fixed solely on the operating environment of continental Europe). The Royal Air Force maxim that "the bomber will always get through" applied as much to ships as to targets in the UK. When the US Air Force became a separate and equal service in 1947, it would attempt to place similar pressures on US Naval Aviation (and indeed, on the size and composition of the whole Navy); the result of this was an inter-service conflict which became known as the Revolt of the Admirals.
The British approach of armoured flight decks was an effective form of passive defence from bombs and kamikaze attacks that actually struck their carriers, but the American system proved more effective in preventing the carriers from being hit in the first place. The larger air groups (90-100 planes, vs. 45-55 for British ships) allowed a far more effective combat air patrol (CAP), improving the protection of the whole battle group and lessening the workload of the carrier escorts. Carrier fighters were able to shoot down far more kamikaze aircraft than any amount of deck armor would have protected against. Many kamikaze hits also missed the deck armor entirely and bounced off the decks anyway, as they frequently did against American carriers as well, or did no more damage than they would have against an American ship (the only fleet carrier lost to kamikaze attack was an American light carrier of the Independence class, USS Princeton (CVL-23), which had no deck armor at all; many escort carriers, also unarmored and with much smaller air groups, were also lost to kamikazes). By the end of the war veteran American fighter pilots in superior F6F Hellcat and F4U Corsair fighters were able to defeat the young, inexperienced and ill-trained kamikaze pilots with ease. More importantly, as was found after the war, the lower deck armor made certain that the bombs and kamikaze craft which did hit, tended to do their damage outside of the ship's structure, and two American carriers of the Essex class (Bonhomme Richard and Franklin) survived some of the worst kamikaze hits of the war. While British carriers could take direct hits from bombs then clear the decks and resume operations again the impacts proved to have a long term effect on the structural integrity of the ship and their post war life was shortened. HMS Formidable (R67) was an excellent example of this; while she weathered a severe kamikaze hit in 1945 which cratered her deck armor, the hit caused severe internal damage and permanently warped the hull; she was written off during the 1947 survey of the postwar fleet as beyond economical repair and lingered in reserve until 1956 before being towed off to the breakers. Two of her sisters fared just as poorly. Illustrious suffered a similar battering and after the war was limited to 22 knots because of accumulated war damage; she spent five years as a training and trials carrier (1948-53) and was disposed of in 1954. Indomitable was completely refit to like-new condition, only to suffer a severe gasoline explosion onboard, which warped her hull. The explosion occurred on the hangar deck, and while severe, would have been shrugged off by an Essex-class carrier, which returned to service after far worse explosions. She was patched with concrete for Queen Elizabeth II's Coronation Review, then immediately afterward towed to the breakers.
Many of the American carriers that fought in the Pacific and absorbed a great number of hits later served long careers into the 1960s and 70s. Again, an important difference in American versus British naval doctrine showed itself. The Royal Navy concentrated on getting as many carriers in the water as possible, without concern to their viability as postwar fleet units, while the United States Navy, with its very large and capacious shipyards on the East and West Coasts, was able to require a very high standard of construction from its yards while still maintaining a rapid rate of production. Light carriers and escort carriers, on the other hand, were built entirely with a view to short-term availability over long-term utility, and their brief careers showed this fact. British naval historian D.K. Brown put the practical difference between American and British design philosophies in no uncertain terms: "More fighters would have been better protection than armour." The benefits of flight deck armor proved chiefly ironic in nature: Fewer aircraft meant a lower priority to attack than the more heavily-armed American carriers (American warships suffered ten massed suicide attacks, under Operation Kikusui, during the Okinawa campaign to none suffered by British ships), and less ammunition and aviation fuel meant less kindling in the event of a fire.
While flight deck level armor was eventually adopted by the Americans for the Midway design, the strength deck remained on the hangar level. Midway had originally been planned to have a very heavy gun armament (8" weapons). The removal of these weapons freed up enough tonnage to add 3 inches of armor at the flight deck level. While this made a great deal of sense from an air group perspective, the Midway ships sat very low in the water for carriers (due to their much greater displacement), certainly much lower than the smaller Essex-class carriers, and had a great deal of difficulty operating in high seas. Late-life refits to Midway to bulge her hull and improve freeboard instead resulted in reducing the ship's stability, and make flight operations impossible even in moderate seas. The supercarriers of the postwar era, starting with the Forrestal class - nearly 200 feet longer and 100 feet beamier than their World War II counterparts - would eventually be forced to move the strength deck up to the flight deck level as a result of their great size; a shallow hull of those dimensions became too impractical to continue. As before, however, the USN continued to design its ships for large air groups, continuing to reason that the best defence was a good offence.
Landing on flight decks
Landing arrangements were originally primitive, with aircraft simply being "caught" by a team of deck-hands who would run out from the wings of the flight deck and grab a part of the aircraft to slow it down. This dangerous procedure was only possible with early aircraft of low weight and landing speed. Arrangements of nets served to catch the aircraft should the latter fail, although this was likely to cause structural damage. Landing larger and faster aircraft on a flight deck 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, travelling at 150 miles per hour (240 kilometres 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. During World War 2, large net barriers would be erected across the flight deck in order that aircraft could be parked on the forward part of the deck and recovered on the after part. This allowed increased complements, but resulted in lengthened turn-around times as aircraft were shuffled around the carrier to allow take-off or landing operations.
Aircraft are given extra speed to assist take-offs by catapults.
Modern innovations
Angled flight deck
A British innovation was the angled flight deck (or simply, the "angle"), in which the aft part of the deck is widened and a separate runway positioned at an angle. It was tested on the American aircraft carrier USS Antietam (CVA-36), and subsequently adapted as the SCB-125 upgrade for the Essex class and SCB-110/110A for the Midway class. The design of the Forrestal class was modified immediately upon the success of the Antietam configuration, with Forrestal and Saratoga modified while under construction to incorporate the angled deck. 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 angled deck also allows the ship to conduct concurrent launch and recovery operations. The development of the angle provides several advantages, as they improved flight operations, allowed a larger island to be mounted (improving both ship-handling and flight control), drastically simplified aircraft recovery and deck movement (aircraft now launched from the bow and re-embarked on the angle, leaving a large open area amidships for arming and fuelling), damage control and a host of other functional improvements. Because of its utility in flight operations, the angled deck is now a defining feature of STOBAR and CATOBAR equipped aircraft carriers.
Ski-jump
Another British innovation is the ski-jump, which came about as means of improving take off for the VSTOL BAe Sea Harrier "jump jet" on the small aircraft carriers also known as "through deck cruisers". These ships replaced the Royal Navy's full size carriers. The ski jump is a ramp which is curved upwards at its forward end. This converts the short run up available into vertical motion and reduces the fuel used at take off compared to a vertical take off. A disadvantage of the ski jump against catapults, is that it limits a carrier to tactical roles and makes resupply more difficult, as large aircraft and fully-laden fighter-bombers do not have enough of a thrust-weight ratio to take off unassisted from the limited area of a carrier deck.
See also
Categories
Naval aviation