二次世界大戰資料庫 (WW2DB)

Contributor: David Stubblebine

This article refers to the entire Essex-class; it is not about an individual vessel.

ww2dbaseFrom the conversion of the collier Jupiter into the carrier Langley in 1920 to the laying down of the last Yorktown-class carrier USS Hornet in 1939, the evolution of the United States Navy's eight aircraft carriers had come a long way from nothing fairly rapidly. However, Wasp and Hornet had not yet even been completed when lessons learned aboard the earlier six carriers convinced Navy planners that another design improvement was warranted.

ww2dbaseDesign work on a new carrier design began in earnest in 1939 with Commander Leslie Kniskern as the primary design officer at Bureau of Ships. Commander Kniskern coordinated input from a variety of specialists including naval architects, experts on aircraft catapults and arresting gear, aviation service units, and of course aviators. A good deal of input came from the Carrier Desk Officer at the Bureau of Aeronautics, Commander James Russell. Russell was the first naval aviator to land on all of the Navy's pre-war aircraft carriers and had just finished two years aboard USS Yorktown (Yorktown-class), including close involvement in the carrier's initial fitting out. His practical carrier experience both as an aviator and as a ship's officer proved invaluable to Kniskern's team.

ww2dbaseAll previous carriers had been constructed within the guidelines of the international naval treaties of their day. With the lapse of the Washington Treaty in 1936, it became possible to increase carrier tonnage to the new levels set by Congress in 1938. At the Bureau of Ships, the top design priority for these new carriers was a requirement for them to fit through the locks at the Panama Canal and so this, then, became the deciding factor for the upper limits of the new carriers' size.

ww2dbaseThe second of the priorities came from something known as the "Sunday Punch." Since the sole purpose of an aircraft carrier is to launch aircraft as a projection of force, the design specification was created for the new ships to have a compliment of 90 aircraft with all 90 able to be spotted on the flight deck at the same time for a fully armed deck-load launch in a single strike – the Sunday Punch. With naval aircraft getting larger, this would require more square footage than earlier classes and with naval aircraft getting heavier, this would require more free deck forward for the take-off roll. Catapults were part of the design but were viewed as optional given the carrier aircraft of the day and the helpful effects of ocean winds blowing across the deck. Even so, the requirement to spot 90 planes on the deck ready for launch was a challenge for the designers. Using a scaled-up version of the Hornet as a starting point, they found some of this extra space by eliminating the starboard gun gallery and extending the flight deck over those spaces. The 5-inch guns were repositioned into four twin-turrets on the flight deck, two before and two abaft the island, which was also reduced in size to create more flight deck space. The Wasp (Wasp-class) had put to sea by this time and her experiment with an aircraft elevator at the edge of the flight deck instead of along the deck's centerline had already met with resounding approval. Since the new ship also needed to fit through the Panama Canal, the specification was created for a deck edge elevator that could fold up for passage through the canal. All of these features, along with a few other tricks, added to the useable flight deck space.

ww2dbaseThere was also serious consideration given to the question of whether or not to armor the flight deck. Naval architecture requires placing as much of the ships' weight as possible in the lower parts of the ship; the closer to the waterline the better and below the waterline better still. A large armored flight deck with all the structural supports needed to hold it up would put significant weight high in the ship, with the added problem of reducing the useable hangar deck spaces due to the larger size and number of structural members. Along with other considerations, the decision was made early on to not armor the flight deck but to armor the hangar deck and also the fourth deck instead. From an architectural perspective, the hangar deck became the ship's main deck. Reducing the weight of the flight deck also allowed that deck to be raised a bit higher, opening the vertical space in the hangar deck even more. A sort-of half-deck, the Gallery or Mezzanine Deck, was to be suspended from beneath the flight deck for aviation squadron ready-rooms and the Combat Information Center. The flight deck surface was to be made of wood; teak beams laid athwartships (crossways) in steel channels with every twelfth cross-channel having steel tie-down slots for the lashing down of aircraft. If damaged, these wooden planks could be easily and quickly replaced using few tools and thus restore the deck for flight operations. This ability to quickly repair a damaged flight deck at sea to get the ship back in the fight was another reason the flight deck was not armored, since damage to an armored deck would almost certainly require repairs at a shipyard. In 1940 at the Navy Yard in Washington DC, no one was considering the prospect of kamikaze-type attacks.

ww2dbaseDuring the conversation about how to maximize the space on the flight deck, Commander Russell, the aviator, pushed hard for the flight deck to be rectangular all the way to the bow. His reasons were only partly about having more space for spotting aircraft but was more about giving pilots the full width of the deck for take-off, where the most vulnerable moment would be at the very end of the take-off roll. The naval architects resisted this idea based of the structural support that would be needed at the forward corners where the ship's hull would be the narrowest. Once the decision was made to not armor the flight deck and lighten the deck with wood, Commander Russell brought this idea up again. The architects said a deck with wide corners supported only in the middle would fail structurally in heavy seas and buckle. The aeronautic people at the table convinced the designers that an occasional buckled deck was worth the trade-off of having a safer take-off platform and more space to spot planes. The rectangular flight deck was approved [Note: In June 1945, at a time when 16 Essex-class carriers were in commission, the fleet steamed through a typhoon southeast of Japan and of the six carriers in that storm, two suffered buckled flight decks precisely as the architects had predicted; this was the third typhoon Essex-class carriers sailed through and these were the only instances of buckled flight decks].

ww2dbaseIn many areas of the design, specifications called for the use of Special Treatment Steel (STS), a nickel-chromium steel alloy that had the same protective qualities as Class B armor but was less prone to splintering and was fully structural rather than just deadweight. STS was used extensively as a structural material wherever armor protection was desirable, including the hangar deck, the fourth deck, the pilot house, the bulkheads surrounding the boiler and engine rooms, around the steering works, and many other areas of the ship.

ww2dbaseSeveral design innovations were used in the ship's powerplant as well. Steam turbines were chosen over the turbo-electric designs of Langley and the Lexington-class. There would be four boiler rooms and two engine rooms arranged along the center-line of the ship. Each boiler room had two Babcock and Wilcox boilers operating at 850°F (450°C). The engines were Westinghouse steam turbines with each consisting of paired low-pressure and high-pressure turbines connected to double-reduction gears. The low-pressure turbines were used for better efficiency at lower cruising power but were bypassed with the steam fed directly to the high-pressure turbine for higher power. Altogether, the engines were capable of producing 150,000 horsepower to four propeller shafts with maximum headway over 30 knots.

ww2dbaseThe spaces below the waterline received special attention from the planners and their internal design was integrated with the specifications for the hull's outer armor plate. The underwater armor extended 17 feet below the waterline and was designed to withstand up to 500 pounds (230 kg) of TNT. This was not enough to withstand the large Japanese torpedoes but could localize the damage. The interior spaces consisted of two outer fuel oil tanks and two inner void spaces with the frames staggered to avoid transmitting the shock of an explosion too deeply into the ship. The hull was also given a triple bottom against magnetic mines.

ww2dbaseFuel capacity and fuel handling was another area that required special and innovative planning, both for the ship's fuel and for the aviation fuel. The carrier's range specifications required a fuel oil capacity of 6,330 tons (1.5 million gallons) and aviation fuel capacity of 240,000 gallons.

ww2dbaseSeveral features were designed into the ship with respect to safely handling the volatile aviation gasoline. First, the fuel was divided between three tanks with one center tank, one saddle-shaped tank over the center tank as well as along both sides, and another saddle-shaped tank over and alongside both of the other two. In this way, as fuel was used up from the outside tanks toward the middle, the tanks were filled with seawater to create additional protection buffers between the hull and the remaining fuel. Second, the fuel itself was not pumped to the fight deck or hangar deck; instead seawater was pumped into the fuel tanks and as the water level rose at the bottom of the tanks, the fuel floating on top was forced up the risers and delivered where it was needed. This created two main advantages: the fuel tanks were never partially full with dangerous gasoline vapors building up inside them, and after each fueling operation the system would dump a particular amount of seawater out of the tanks to lower the fuel levels and drain the risers. This feature was also used to quickly empty the fuel supply system on the hangar deck and flight deck in the event of fires on those decks.

ww2dbaseThe build-up of gasoline vapors inside the hangar deck was identified as a problem in earlier carrier designs so the new carriers were to have well ventilated hangar deck spaces. This was accomplished through a by-product of not armoring the flight deck; the lack of heavy structural flight deck supports allowed for large openings along the edges of the full length of the hangar deck that could be individually closed off as needed. This feature proved very beneficial later on when the carriers came under attack and burning aircraft and loose ordinance could be easily and quickly pushed over the side through these openings.

ww2dbaseMany of the aviation facilities of the new design were direct carry-overs from the preceding Yorktown-class. The new design called for two aircraft catapults on the flight deck with one hangar deck catapult, as before, but in actual production the catapult arrangements varied from ship to ship. There were three aircraft elevators as before, but one was moved to the deck edge. Also, the elevators were positioned to partition the hangar deck into quarters that could then be used by aircraft handlers and mechanics for different specialized purposes. The number of arrestor cables crossing the deck for aircraft landings was increased to sixteen. Something new were a set of arrestor cables across the bow as well with a performance specification for the class to be able to conduct flight operations while steaming in reverse [Note: The first several Essex-class carriers had to demonstrate this ability during their sea trials and in June 1945 when a typhoon buckled the leading edge of Hornet's flight deck, she launched aircraft over the stern in the only operational use of this capability].

ww2dbaseOnce the design plans were accepted by the Secretary of the Navy in Feb 1940, individual construction contracts were drawn up and awarded to shipyards. The contracts were numbered sequentially with numbers that would become the ships' hull numbers but the contracts were assigned to shipyards in blocks so the ships were not built in that same order. The first block of contracts was split between the Newport News Shipbuilding Company in Newport News, Virginia and the Bethlehem Steel Corporation at the Fore River Shipyard in Quincy, Massachusetts; seven to Newport News and four to Quincy. Later, smaller blocks were awarded to the New York Navy Yard, the Norfolk Navy Yard, and the Philadelphia Navy Yard. Still later, three more contracts were awarded to Newport News and one more to Quincy, for a total of 24 ships of the class. Actual construction began with the laying of the Essex keel on 28 Apr 1941 and by the time of the Pearl Harbor Attack six months later, five Essex-class carriers were under construction. The original block of seven contracts awarded to Newport News became Essex, Yorktown, Intrepid, Hornet, Franklin, Ticonderoga, and Randolph; the four at Quincy became Lexington, Bunker Hill, Wasp, and Hancock.

ww2dbaseThough not designed with mass production in mind, several of the design elements, like the large number of flat steel surfaces, greatly assisted shipbuilders and nearly every one of the carriers beat their projected construction schedules by about half. Design modifications were still being made even as construction was underway and also after ships went into service. Often the changes were on an individual ship-by-ship basis and in the end, no two ships of the class were truly identical. Some changes were small and some were more significant. Many of the differences between ships centered on the radar configurations, since that technology was changing very rapidly. Starting with Bennington laid down 15 Dec 1942, certain reconfigurations were introduced into the design. The hangar deck aircraft catapult was eliminated as unnecessary (although the first two carriers, Essex and Lexington, never had one). Gun directors were added or relocated and the Central Intelligence Center was moved to an armored location. Lessons learned in battle led to a need for more anti-aircraft gun mounts and so starting with the ships laid down in 1943, twin 40mm mounts were added on the bow just below the level of the flight deck and another on the stern. To make room for them, the bow and stern were extended slightly, adding 16 feet to the overall length of the ship. In later years, this extra 16 feet gave rise to distinguishing some ships as Long-Hull Essex-class and the others as Short-Hull Essex-class. Some sources went so far as to call the Short-Hulls Essex-class and the Long-Hulls Ticonderoga-class. All of these were post-war distinctions made mainly by model makers and addressed differences the Navy ignored; to the Navy they were all simply Essex-class.

ww2dbaseA total of seventeen Essex-class carriers were commissioned during World War II with fourteen sailing into the combat zones, all in the Pacific and amassing 88 battle stars. Seven more ships of the class went into service after the war until the class was superseded by the larger Midway-class. Some Essex-class carriers suffered tremendous battle damage during World War II but none were sunk by enemy action. Even as Oriskany, the last of the class to be commissioned, was being intentionally sunk as an artificial reef off the Florida coast in 2006, the quality of the design made the ship very reluctant to slip beneath the surface.

ww2dbaseBunker Hill and Franklin were so badly damaged in 1945 that soon after the war, they were taken out of service and scrapped. Of the remaining ships that served into the 1950s, all but one (Boxer) were modified with an enclosed reinforced bow and an angled flight deck that was essential for landing post-war jet aircraft. Nearly every ship of the class that served into the 1950s and 1960s saw further combat service during the Korean and Vietnamese conflicts.

ww2dbaseThe second Essex-class ship to be commissioned, USS Lexington, was the last to be taken out of service in 1991, over 48 years after she first sailed (although not all continuous service). Presently, four ships of the class survive as museum ships, Lexington (Texas), Intrepid (New York), Yorktown (South Carolina), and Hornet (California).

ww2dbaseEssex-class carriers (in order of commissioning with World War II Battle Stars):

Essex 級 航空母艦 互動地圖

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Essex 級 航空母艦 Operational Timeline

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