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SCB-27, or "Two Seven-Alpha"/"Two Seven-Charlie," was the United States Navy designation for a series of upgrades to the Essex class aircraft carriers (both the short-hull and long-hull (Ticonderoga) versions), conducted between 1947 and 1955. These upgrades were intended to allow the World War II-era carriers to operate jet aircraft.


USS Hornet showing her SCB-27A configuration.

Officially, Ship Characteristics Board Program 27 proper referred to the completion of USS Oriskany (CV-34), left unfinished at war's end, to a heavily revised design; reconstructions of earlier ships were programs SCB-27A and 27C. The SCB-27 modernization was very extensive, requiring some two years for each carrier. To handle the much heavier, faster aircraft of the early jet-era, the flight deck structure was significantly reinforced, able to support aircraft weighing up to 52,000 pounds (23,587 kg), namely the North American AJ Savage. Stronger and larger elevators, much more powerful catapults, and new Mk 5 arresting gear were installed. The original four twin 5"/38 gun mounts were removed, clearing the flight deck of guns. The new five-inch gun battery consisted of eight weapons, two on each quarter beside the flight deck. Twin 3"/50 gun mounts replaced the 40mm guns, offering much greater effectiveness through the use of proximity fuzed ammunition. The reconstruction eliminated the difference between "short-hull" and "long-hull" ships; all now had similar clipper bows.

The island was completely redesigned, made taller, but shorter in overall length with the removal of its gun mounts. In addition, the boiler uptakes were rebuilt and angled aft to accommodate a single radar and communications mast atop the island. To better protect aircrews, ready rooms were moved from the gallery deck to below the armored hangar deck, with a large escalator on the starboard side amidships to move flight crews up to the flight deck. Internally, aviation fuel capacity was increased to 300,000 US gallons (1,135,624 L) (a 50% increase) and its pumping capacity enhanced to 50 US gallons (189.3 L) per minute.[1] Fire fighting capabilities were enhanced through the addition of two emergency fire and splinter bulkheads to the hangar deck, a fog/foam firefighting system, improved water curtains and a cupronickel fire main. Also improved were electrical generating power, and weapons stowage and handling facilities. All this added considerable weight: displacement increased by some twenty percent. The armor belt was removed and blisters were fitted to the hull sides to compensate, widening waterline beam by eight to ten feet. The ships also sat lower in the water, and maximum speed was slightly reduced, to 31 knots.

Modification sub-types

USS Intrepid CVA-11 showing her SCB-27C configuration.

The two sub-types of SCB-27 modifications were primarily a result of changes in catapult technology in the early-1950s. SCB-27A vessels utilized a pair of H 8 slotted-tube hydraulic catapults, while the later SCB-27C vessels were fitted with a pair of C 11 steam catapults, a British innovation (in fact the first four installed, on USS Hancock and USS Ticonderoga, were British-built). To accommodate the catapult machinery, the SCB-27C vessels were slightly heavier (43,060 vice 40,600 tons) and after bulging wider abeam (103 vice 101 feet) than their SCB-27A sisters. Additionally, the SBC-27C carriers were equipped with jet blast deflectors, deck cooling, fuel blending facilities, emergency recovery barrier and storage and handling for nuclear weapons, which was not included in all of the SCB-27A carriers. Under SCB-27C the No. 3 (after) elevator was moved to the starboard deck edge; this elevator was located further aft on the first three SCB-27C ships than it was on the ships which received it concomitantly with an angled flight deck under the SCB-125 program.[1] The greater capacity of steam catapults meant that the 27C ships were able to serve as attack carriers through the Vietnam era while their hydraulic-equipped 27A sisters were relegated to antisubmarine duties.

Program history

USS Oriskany (CV-34), laid up incomplete at the conclusion of World War II, served as the prototype and was re-ordered to the SCB-27 standard. All of the SCB-27 modernized Essex carriers, save USS Lake Champlain (CV-39), were further modified under the SCB-125 modernization program.

Modified vessels [2]

View of the characteristic escalator below the island, here on USS Hornet.

  Program Shipyard Work Began Recommissioned
USS Oriskany (CV-34)   SCB-27   New York   Aug 1947   Sep 1950
USS Essex (CV-9)   SCB-27A   Puget Sound   Feb 1949   Jan 1951
USS Wasp (CV-18)   SCB-27A   New York   May 1949   Sep 1951
USS Kearsarge (CV-33)   SCB-27A   Puget Sound   Feb 1950   Feb 1952
USS Lake Champlain (CV-39)   SCB-27A   Norfolk   Aug 1950   Sep 1952
USS Bennington (CV-20)   SCB-27A   New York   Dec 1950   Nov 1952
USS Yorktown (CV-10)   SCB-27A   Puget Sound   Mar 1951   Feb 1953
USS Randolph (CV-15)   SCB-27A   Newport News   June 1951   Jul 1953
USS Hornet (CV-12)   SCB-27A   New York   July 1951   Sep 1953
USS Hancock (CV-19)   SCB-27C   Puget Sound   Dec 1951   Feb 1954
USS Intrepid (CV-11)   SCB-27C   Newport News   Apr 1952   Jun 1954
USS Ticonderoga (CV-14)   SCB-27C   New York   Apr 1952   Sep 1954
USS Shangri-La (CV-38)   SCB-27C/125   Puget Sound   Oct 1952   Jan 1955
USS Lexington (CV-16)   SCB-27C/125   Puget Sound   Sep 1953   Aug 1955
USS Bon Homme Richard (CV-31)   SCB-27C/125   Hunters Point   May 1953   Sep 1955


  1. 1.0 1.1 Friedman, Norman (1983). U.S. Aircraft Carriers: An Illustrated Design History. Annapolis: Naval Institute. ISBN 0-87021-739-9. 
  2. "U.S. Navy Ship Types - SCB-27 modernization of Essex/Ticonderoga class aircraft carriers". U.S. Navy Historical Center. 2001-10-08. Retrieved 2006-12-04. 

Portions of this entry were drawn from: Naval Historical Center SCB-27 information and photos

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