Essex Class, U.S. Fleet Carriers

National Archives #80-G-68097

ONI 222

Specifications:

The Essexes were completed in 1942-1945 and were the definitive American carrier class of the war. Though not designed with mass production in mind, they became the most numerous class of capital ship ever constructed by the United States. Already regarded as obsolescent by the end of the Pacific War, due to the legacy of the treaty restrictions reflected in their original specifications, they were nonetheless a highly successful ship class.

The new class was first proposed in May 1939 and was originally to be a single ship, which would use the carrier tonnage remaining under the Vinson-Trammell Act of 1934 after the construction of Hornet. The displacement of this carrier was limited by statute to 23,000 tons, which permitted only a modest improvement on the previous Yorktown class. However, as war clouds gathered and the naval disarmament treaties became moot, the United States saw the need for a greatly expanded Navy. Statutory tonnage restrictions were relaxed and additional ships were ordered (three in early 1940 and another seven after the fall of France.) Five of these were laid down before war broke out in the Pacific. Two more were ordered in 1941 and another 13 in 1942 and 1943. A total of 17 were commissioned by August 1945, and 15 reached the combat zone before the war ended. Seven more were completed postwar, but the remaining two, plus six ordered in 1944, were canceled in favor of the Midway class. 

The design incorporated the lessons of the Yorktowns, which had been in service just long enough for their superiority over the Lexingtons and Ranger to be evident. The final design was 7000 tons larger than the Yorktowns, and while this was not as large as naval aviators might have wished, the limited size worked to advantage, allowing the ships to be produced in large numbers.

The design emphasized offensive fighting power rather than passive defense. The ships' own aircraft were considered its most important protection, and the single most important design criterion was the ability to launch a large deck load strike. The ships were required to be able to spot four full squadrons of modern aircraft on the flight deck for a single launch while a reserve squadron was warming up on the hangar deck.Most of the increased tonnage therefore went into increasing the flight deck area and providing increased stores of aviation gasoline. Other measures to increase flight deck area included moving the squadron ready rooms and the CIC into the gallery deck, immediately beneath the flight deck, in order to minimize the width of the island. This also made it possible for each squadron to have its own air-conditioned ready room, which improved pilot readiness, but at the cost of putting these important spaces where they would be vulnerable to hits on the flight deck.

The air group was initially specified as four squadrons of 18 aircraft, as with earlier American carriers, plus the reserve fighter squadron and space for 25% replacement parts. However, improvements in aircraft spotting based on early war experience meant that the reserve squadron became part of the standard air group almost as soon as the ships entered service. By the end of the war as many as 102 aircraft were operated (6 fighters, 66 fighter-bombers, 15 dive bombers, and 15 torpedo bombers.) Experience with the postwar Midways showed that this was just about the largest air group that could reasonably be operated off of a single carrier.

Gasoline storage was generous compared with previous classes. The Navy expected the carriers to be able to steam at 25 knots for sixteen days, with air operations on ten of those days, and with each aircraft operating up to eight hours a day at an average fuel consumption rate of 37 gallons per hour.This led to a fuel capacity requirement of 240,000 gallons of aviation gasoline.

The armor protection was designed against 6" shells only and did not include the hangar deck. This permitted a large air group and an open hangar design that allowed aircraft to warm up their engines on the hangar deck. However, the unprotected hangar proved vulnerable to bomb damage and kamikaze attack, particularly when armed and fueled aircraft were present. Though none of these ships were sunk during the war, Franklin and Bunker Hill took horrible damage from fires and secondary explosions after being hit in their hangar decks. Their survival was a tribute both to the design of the ships and the quality of American damage control procedures and training.

One of the few clear design flaws was the requirement that the ventilation intakes be located beyond the ends of the armored hangar deck in order to minimize openings in the armor. The resulting single long ventilation trunk became a conduit for smoke and burning gasoline, which proved disastrous on Franklin when she was hit by a kamikaze. Postwar reconstruction eliminated this flaw.

The underwater protection system was 16'9" deep and designed to withstand up to 500 pounds (230 kilograms) of TNT. This was inadequate to prevent penetration by the large Japanese torpedo warheads but was enough to localize damage. The system consisted of two outer compartments of fuel oil and two inner void spaces, with the frames staggered to avoid transmitting the shock of an explosion directly to the holding bulkhead. This holding bulkhead consisted of almost 2" (50mm) of Special Treatment Steel (STS) which was highly resistant to splinters. STS was used extensively as a structural material wherever armor protection was desirable, including the hangar deck, the fourth deck, and many other areas of the ship.  However, the underwater protection was neither up to contemporary battleship standards nor even much of an improvement on the Yorktowns, the chief improvement being the relocation of the liquid compartments from the middle to the outer layers of the system.

A triple bottom against magnetic mines was a last-minute addition to the basic design specifications.

The machinery was very robust, as shown by the experience of Franklin, which had her boilers flooded with cold seawater but immediately restored power without serious damage to her propulsion plant. The machinery was divided among four boiler rooms and two engine rooms, the aft engine room driving the inner shafts and the forward engine room driving the outer shafts. Each boiler room had two Babcock and Wilcox boilers operating at 565 psi (3820 kPa) at 850 degrees Fahrenheit (450 degrees Centigrade) employing both preheat and superheat features. The Westinghouse turbines consisted of paired low-pressure and high-pressure turbines driving a double-reduction gearbox. An astern turbine was fitted to the rear of each low pressure turbine and a cruising turbine to the front of each high pressure turbine. The cruising turbine was used for efficiency at low power and was bypassed (the steam being fed directly to the high-pressure turbine) when higher power was needed.

Electrical power was supplied by four 1250 kW turbo-generators tied to the main boilers. Emergency power was supplied by two 250 kW diesel generators in the machine spaces and three 60 kW generators on the hangar deck. Nine separate fire pumps were provided, which were also used for washing the deck and could be used for pumping out flooded compartments.

The antiaircraft battery of twelve 5”/38 antiaircraft guns, supplied with VT (proximity fuse) shells, was a terror to attacking aircraft. It was supplemented by light antiaircraft which, by the time the war ended, consisted of up to 72 40mm guns and 60 20mm guns. Eight of the 5" guns were mounted in twin turrets fore and aft of the island, where they had excellent fire arcs. However, their blast was capable of damaging aircraft on the flight deck, a problem that was corrected in the Midway class by having all its heavy antiaircraft guns mounted on sponsons at the level of the hangar deck.

The ships were designed before the need for special provisions for radar was generally recognized. As a result, radar antennas were crowded onto an already cramped island, which created problems of mutual interference and radar shadows. Radar installations varied widely by ship, but the first units were all completed with SG surface search and SK air search radars, plus a smaller backup SC air search radar on a small mast outboard of the funnel, plus two fire control radars for the 5" guns. Some units added a second SK behind the funnel to cover blind spots. Most units later received SM fighter direction radar, and the air search radars were supplemented with height-finding radar. All the search radars had a blind spot directly overhead, which proved vulnerable to kamikazes and was covered with improvisations based on AN/APS-6 or Army SCR-720 night fighter radar. These were typically installed on a catwalk to avoid interference with the sets on the already-crowded island.

Production was streamlined through the use of highly standardized components, reducing construction time to as little as 14 months. Because of the high priority given the carriers, their construction encountered few bottlenecks. The nation's shipyards were in the process of expansion as the Essex program got rolling, and lack of ways was never a significant bottleneck, though Bethlehem Quincy began laying down two of the five hulls awarded to it on ways that were still under construction. Other yards awarded contracts were Newport News (the lead yard, seven ships), Norfolk Navy Yard (four ship), New York Navy Yard (five ships), and Philadelphia Navy Yard (three ships). All were located on the East Coast.

The first ten ships of the class had bows flush with the forward flight deck. These proved vulnerable to storm damage and the last fourteen ships were completed with their hulls extended 12 feet (4 meters) further forward. This also provided space for four more 40mm guns to provide antiaircraft protection from dead ahead.

If the ships had any particular weakness, other than the wooden flight decks, it was that they lacked stability due to the unexpected weight of the antiaircraft guns, radars, and modern naval aircraft added during the war. Designers feared that three torpedo hits would be enough to capsize one of the ships. However, their stability was never seriously tested in battle.

Units in the Pacific:

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References

Chesneau (1992)

DANFS

Friedman (1983)

Gogin (2010)

Roberts (1982)

Worth (2001)

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