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:''This article refers to the flight deck of an aircraft carrier, 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".

Contents

Evolution

Early flight decks

Full length decks

Armoured decks

Design

Theory

Circumstances

Aircraft Restrictions

Defences

''Midway'' and ''Forrestal'' classes

Landing on flight decks

Modern innovations

Angled flight deck

Ski-jump

Flexible decks

References

See also

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 2 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; thus Dunning also has 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, battlecruisers that otherwise would have had to have been discarded under the Washington Naval Treaty - such as the British HMS ''Furious'' and ''Glorious'' class and the American USS ''Lexington'' and ''Saratoga'' - were converted to carriers along 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 in practice. Because the military effectiveness of aircraft carriers was then unknown, early ships were typically equipped with cruiser-calibre 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 an integral 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. 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 (unarmoured) 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 others that were tried; including second flying-off decks and an anti-aircraft battery (the most common American configuration during World War II). This was latter adopted in the British Illustrious-class and the Imperial Japanese Navy's Taihō.

Armoured decks

The carriers compared are the Royal Navy's (RN) ''Illustrious'' class and their nearest United States Navy (USN) contemporaries, the ''Yorktown'' class and ''Essex'' class. The ''Illustrious'' class followed the ''Yorktown'' but preceded the ''Essex''.

Design

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 different thickness of armour, and how they were distributed, are described in the table below;

Comparative armour thickness of some World War II era aircraft carriers
	Flight deck	Main deck	Side belt
''Yorktown'' class (19,875 tons)	n/a	1.5 in (38 mm)	2.5 – 4 in (64 – 101 mm)
''Illustrious'' class (23,000 tons)	3 in (76 mm)	3 in lateral strakes (76 mm)	4.5 in (114 mm)
''Essex'' class (27,200 tons)	2.5 in (64 mm)	1.5 in (38 mm)	2.5 – 4 in (64 – 101 mm)
''Shōkaku'' class (25,600 tons)	n/a	3.9 in over machinery (99 mm)	1.8 in (46 mm)

Theory

Carrying the armor at the flight deck level would protect the hangar deck and the aircraft stored there from most bombs. The armour of the ''Illustrious'' class was intended to protect against 1,000 pound bombs^[1]. In the ''Illustrious'' class, the armoured flight deck extended for about two-thirds of the length of the ship, bounded by the two aircraft lifts (which were without the armour). The deck was closed by 4.5-inch armoured sides and bulkheads, forming an armoured box. The bulkheads had sliding armoured portals to allow access between the hangar and the aircraft lift. There were 3-inch lateral strakes of main deck armour that extended from the base of the hangar side-wall to the top of the main side belt. The latter protected the machinery, magazines and aircraft fuel and weaponry stores. The hangar was environmentally sealed, which meant that aircraft engines could not be run-up under cover; any work requiring engines to be running had to be carried out on the flight deck.
US and earlier Japanese carriers had their armour placed at the hangar deck, essentially treating the hangar spaces and flight deck as superstructure. A bomb that struck the flight deck would likely penetrate and explode in the hangar deck, but the armor there would still protect the ships innards — including the engine spaces and fuel storage. The flight deck could also possible detonate light bombs prematurely, which would reduce the chance of them going through the hangar deck. Such a design allowed for larger, open-sided hangar bays (improving ventilation) and the installation of deck-edge elevators. Most carriers with hangar deck armour also usually had wooden flight decks which were easy to repair. However, wooden flight decks were particularly vulnerable to burning, so after refuelling, fuel lines in the deck would be purged with exhaust gasses to reduce this danger.

Circumstances

The differences in construction were determined by doctrine that was largely driven by the different circumstances of the USN and RN. The USN had its own aircraft procurement budget and procedures, independent of the Army Air Corps. The RN's Fleet Air Arm (FAA) was constrained inter-war by the influence of the Royal Air Force on developing a strategic bomber force. As a result, in the late 1930s, the FAA did not have any modern high-performance aircraft at its disposal, indeed its first monoplane, the Blackburn Skua, only flew for the first time in 1937. The Royal Navy expected to be fighting a war in the confines of the North Sea and Mediterranean Sea, under the umbrella of land-based enemy air forces¹. By contrast, the USN expected to be operating within the vast expanses of the Pacific Ocean.

Aircraft Restrictions

Within the confines of ship design, and the Second London Naval Treaty to which they complied, the ''Illustrious''-type carriers had to accept lower hangar heights (to keep the metacentric height within acceptable limits) and size, and as a result, a lower complement of aircraft. No British carrier other than the early HMS ''Argus'' had a hangar to match the 20 ft (6.1 m) hangar height of the American ''Lexington'' class or 17 ft 6 in (5.3 m) hangars of the ''Yorktown''-class ships 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.

Defences

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. 45–60 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; near 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. (In addition to larger aircraft complements, the US Navy had larger fleets and more resources, so they could establish destroyer pickets and develop dedicated AAW ships such as the ''Atlanta''-class antiaircraft cruisers which would have also drew attention away the carriers.) On the surface, the record seems balanced.
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 and less ammunition and aviation fuel meant less kindling in the event of a fire. US carriers and their fighters shot down more than 1,900 suicide aircraft during ''Operation Kikusui'' (the last and largest Kamikaze attack in the Okinawa campaign), versus a mere 75 for the British, yet both forces suffered the same number of serious hits (four). The prospects for the survival of the British carriers, had they come under the same volume of attack as their American counterparts, are sobering.
The kamikaze threat overall was not serious, as many kamikaze strikes missed the deck armor entirely, or bounced off the decks of both British or American carriers. The majority of kamikazes that did inflict harm caused no more damage than they would have against a smaller ships. After a successful kamikaze hit, the British were able to clear the flight deck and resume flight operations more quickly than their American counterparts. Royal Navy damage control from kamikaze strikes lasted usually a few hours while it took the Americans a few days.
What was not discovered until late in the war was that the kamikaze impacts proved to have a long term effect on the structural integrity of British carriers 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 structural 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, especially off of Malta in 1941 when hit by German dive bombers and after the war was limited to 22 knots (41 km/h) 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, several of which returned to service after far worse explosions. ''Indomitable'' was patched with concrete for Queen Elizabeth II's Coronation Review, then immediately afterwards towed to the breakers.
By contrast, it was found after the war, the lower deck armor of American carriers made certain that the bombs and kamikaze craft which did hit, tended to do their damage outside of the ship's structure. American carriers of the ''Essex'' class also survived some of the worst kamikaze hits of the war, albeit with high casualties. USS ''Franklin'' was struck by two 250/550 kg/lbs armor-piercing bombs, one of which penetrated her armored hangar floor and set off ammunition, killing 724 personnel. USS ''Bunker Hill'' was severely damaged by pair of kamikaze hits which killed 346 men. As most of the damage was outside of the ship's structure, and combined with higher quality construction of US shipyards (while the British were forced to rush the construction of the ships to get them combat ready, the numerous and capacious American yards on the East and West Coasts allowed the US Navy to build carriers at a more leisurely pace individually while producing ships collectively at a furious rate), this ensured that even significantly damaged carriers could be economically restored to good condition, as the ''Franklin'' and ''Bunker Hill'' were successfully repaired though they saw no postwar service.
The only carrier lost to a deck hit was the American ''Independence''-class light carrier, USS ''Princeton'' (CVL-23). Indeed, many light and escort carriers were unarmored, with no protection on the hangar or flight deck, and thus they fared poorly against deck hits.

''Midway'' and ''Forrestal'' classes

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 in weapons). The removal of these weapons freed up enough tonnage to add 3 inches (76 mm) 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 heavy seas. Late-life refits to ''Midway'' to bulge her hull and improve freeboard instead gave her a dangerously sharp roll, and made flight operations impossible even in moderate seas. This was therefore not repeated on ''Coral Sea'' (''Roosevelt'' had been decommissioned years earlier).
The supercarriers of the postwar era, starting with the ''Forrestal'' class — nearly 200 feet longer and 40 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. The issue of protection had no influence on the change; the Forrestal class and after do not have armored flight decks.
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 arrestor 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 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 II, 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 "bolts", or misses the arresting gear, to become airborne again without concern for aircraft parked forward. (The radio call describing this aborted landing is "bolter, bolter"). 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 Invincible class aircraft carriers (which were, politically, known as "through deck cruisers" during construction). 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.

Flexible decks

An idea tested but never taken to completion was the "flexible deck". In the early jet age it was seen that by eliminating the landing gear for carrier borne aircraft the inflight performance would be improved. This led to the concept of a deck that would absorb the energy of landing, the risk of damaging propellers no longer being an issue though take off would require some sort of launching cradle. ^[2]

References

1. ''British and Empire Warships of the Second World War'', H T Lenton, Greenhill Books, ISBN 1-85367-277-7
2. http://www.thunder-and-lightnings.co.uk/scimitar/history.html Thunder and Lightnings - Scimitar] 21 May 2007

See also

★ Aircraft carrier