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To Keep Up With the Times

The SCB-27 and SCB-125 Modernization Programs

The modernization programs - a visual comparison.

This is a very, very long post about the Essex-class carriers and the Ship Characteristics Board Project 27 (SCB-27) and Project 125 (SCB-125) modifications most of them received in the late 1940s and the 1950s.

The Original Essex-Class

USS Essex (CV-9) at Hampton Roads, Virginia, 1 February 1943.

The image above shows the original Essex-class design. With a straight flight deck, four 5″/38 twin gun mounts near the island and an unenclosed bow, the Essex-class was, in terms of appearance, like an enlarged Yorktown-class. 24 ships of the Essex-class formed the main striking force of the US Navy. No other class of capital ships of the 20th Century was as numerous. However as time goes by, modifications to the ships became necessary to keep them useful. This called for the SCB-27 modernization project.

SCB-27: The Template

USS Oriskany (CV-34) off New York City, 6 December 1950.

USS Oriskany (CV-34) was launched on 3 October 1945, however she was not commissioned until 25 September 1950, almost five whole years later. What took them so long? The answer: her construction was suspended in 1947, and she was converted to an updated design.

As the prototype for the SCB-27 program, she differed from her sisters. She had a massively reinforced flight deck so that she could handle heavier aircraft (up to 52,000 pounds). She also had stronger elevators, more powerful hydraulic catapults, and new arresting gear to come with that. As you may have noticed, she carried no 5″/38 gun mounts near the island. Her island had been completely redesigned, being taller but shorter in length. Though not quite visible from the photograph, she received  3″/50 anti-aircraft guns instead of the 40 mm Bofors. Also not visible are the added bulges, which made her more stable and provided additional buoyancy. It also provided additional fuel capacity, and the added weight of the fuel helped reduce the negative effects the increased topside weight had on the ship’s stability.


USS Hornet (CV-12) after SCB-12A modernization, 10 January 1954.

Officially the SCB-27 referred only to the completion of USS Oriskany (CV-34). The reconstructions of the other Essex-class ships were classified as Program 27A (SCB-27A) and Program 27C (SCB-27C). The SCB-27A ships were built following the template set by USS Oriskany (CV-34). Many improvements were made to the ships, which improved their damage control capabilities. Even though their armor belts were removed, the ships had an increased displacement, they sat lower in the water than they did before, and their maximum speed was slightly reduced to 31 knots. The reconstruction also eliminated the differences between “short-hull” and “long-hull” ships.


USS Intrepid (CVA-11) operating off Guantanamo Bay, Cuba, 9 February 1955. After her SCB-27C modernization.

The two sub-types, SCB-27A and SCB-27C, were mainly a result of the rapid advances made in aircraft catapult technology during the 1950s. While most other features were similar if not identical, SCB-27A vessels had a pair of Type H, Mark 8 hydraulic catapults, and the later SCB-27C vessels were fitted with C-11 steam catapults. The Type H, Mark 8 catapults had a maximum load of 15,500 lb at 105 knots, and the much more powerful C-11 had a maximum load of 70,000 lb at 108 knots. The modern steam catapult, a British invention, enabled the SCB-27C vessels to launch much heavier aircraft than their SCB-27A sisters. The much greater capacity of the steam catapults gave the SCB-27C vessels the ability to serve much longer as attack carriers (CVA) than their SCB-27A sisters, while the latter were relegated to anti-submarine duties as anti-submarine (CVS) carriers.

Due to the differences in catapults utilized, SCB-27C vessels were slightly heavier and had a beam 2 feet wider. Additionally, the aft elevators of SCB-27C vessels were moved from inboard to the starboard deck edge.

The First Built-to-be-Angled Flight Deck: USS Antietam (CVA-36)

USS Antietam (CVA-36) underway, circa 1953. 

In December of 1952, USS Antietam (CVA-36) emerged from the New York Naval Shipyard as the world’s first aircraft carrier with a true angled flight deck. While the principle was devised by Royal Navy Captain (later Rear Admiral) Dennis Cambell and had been tested on other vessels (namely HMS Triumph and USS Midway) before, she was the first carrier to have an angled flight deck installed on a sponson, giving her the “modern carrier” appearance. The angled deck, which allowed concurrent launch and recovery operations, was found to be superior to the old fore-to-aft straight flight deck.


Top: USS Yorktown (CVS-10) underway, 18 June 1962. SCB-27A/125.
Bottom: USS Lexington (CVA-16), circa September 1955. SCB-27C/125.

In the 1950s all SCB-27 vessels received the SCB-125 modernization, with the exception of USS Lake Champlain (CV-39). USS Oriskany (CV-34) is a special case, and we will get to that later.

While the SCB-125 program drastically altered the appearance of the vessels, it involved less changes to the ship’s existing structures than the SCB-27 program did and the SCB-125 reconstruction took around six to nine months, compared to the two years the SCB-27 reconstruction required.

The most visible changes include the angled flight deck and the enclosed hurricane bow. For SCB-27A ships, the aft elevator was moved from inboard to the starboard deck edge. For SCB-27C ships this had been done already. The forward elevator of SCB-27C ships was lengthened, giving the elevator a pentagonal shape. This might be the most visible difference between SCB-27A/125 ships and their SCB-27C/125 sisters.

Besides changes to the flight deck, the bow and the elevators, all ships also received the new mirror landing aid system. In addition the Primary Flight Control was moved to the aft end of the island. A more effective Mark 7 arresting gear was also installed on all vessels, together with air conditioning systems.

SCB-125A: USS Oriskany (CVA-34)

USS Oriskany (CVA-34) underway near Midway Atoll, 1967.

As the prototype for the SCB-27 program, USS Oriskany (CV-34) received the SCB-125 modernization last. As a result she received further enhancements, and she was referred to officially as an SCB-125A vessel, to distinguish her from her slightly different sisters. She received the new Mark 7-1 arresting gear, an improvement over her sisters’ Mark 7 ones. She also had more powerful C 11-1 steam catapults, plus aluminium flight deck cladding. She was the only SCB-27A vessel to receive steam catapults.


USS Yorktown (CVS-10) underway with escorts during Exercise Sea Imp, 1966.

In the 1960s, as part of the Fleet Rehabilitation and Modernization II (FRAM II) program, SCB-144 modernization was carried out to improve the anti-submarine capabilities of eight carriers (seven angle-deck SCB-27A ones and a SCB-27C one). A new SQS-23 bow-mounted sonar dome was installed, together with a stem hawsepipe and a bow anchor. Modifications were also made to the Combat Information Center (CIC).

But wait there’s more: Landing Platform Helicopter (LPH)

USS Valley Forge (LPH-8) underway, circa 1963.

Not all Essex-class ships received an angled deck. While five of them were never reconstructed (plus USS Antietam (CV-36) served as a test bed for the experimental angled deck), three of the class, USS Boxer (CVS-21), USS Princeton (CVS-37) and USS Valley Forge (CVS-45) were converted to amphibious assault ships, more specifically Landing Platform Helicopter (LPH). While they retained the original straight deck and unenclosed bow, their internal compartments were almost completely rebuilt.

U.S. Navy pilot Lieutenant (Junior Grade) Denny Earl of attack squadron VA-163 Saints, Carrier Air Wing Sixteen (CVW-16), with both legs shattered by North Vietnamese anti-aircraft fire, successfully lands his Douglas A-4E Skyhawk attack plane aboard the aircraft carrier USS Oriskany (CVA-34) in the Gulf of Tonkin, 20 October 1967. The nylon emergency barrier assures the wounded pilot that he will not have to make more than one attempt to land his plane.

Two Vought A-7B Corsair II’s from Attack Squadron VA-215 “Barn Owls” in flight. VA-215 was assigned to Carrier Air Wing 19 (CVW-19) aboard USS Oriskany (CVA-34) for a deployment to Vietnam from May to December 1971. 1971. USN Photo. 1971.