Escort carrier

In the early 1920s, the Washington Naval Treaty imposed limits on the maximum size and total tonnage of aircraft carriers for the five main naval powers. Later treaties largely kept these provisions. As a result, construction between the World Wars had been insufficient to meet operational needs for aircraft carriers as World War II expanded from Europe. Too few fleet carriers were available to simultaneously transport aircraft to distant bases, support amphibious invasions, offer carrier landing training for replacement pilots, conduct anti-submarine patrols, and provide defensive air cover for deployed battleships and cruisers. The foregoing mission requirements limited use of fleet carriers′ unique offensive strike capability demonstrated at the Battle of Taranto and the Attack on Pearl Harbor. Conversion of existing ships (and hulls under construction for other purposes) provided additional aircraft carriers until new construction became available.

Conversions of cruisers and passenger liners with speed similar to fleet carriers were identified by the U.S. as "light aircraft carriers" (hull classification symbol CVL) able to operate at battle fleet speeds. Slower conversions were classified as "escort carriers" and were considered naval auxiliaries suitable for pilot training and transport of aircraft to distant bases.

The Royal Navy had recognized a need for carriers to defend its trade routes in the 1930s.[1] While designs had been prepared for "trade protection carriers" and five suitable liners identified for conversion, nothing further was done mostly because there were insufficient aircraft for even the fleet carriers under construction at the time. However, by 1940 the need had become urgent and HMS Audacity was converted from the captured German merchant ship MV Hannover and commissioned in July 1941.[2] For defense from German aircraft, convoys were supplied first with fighter catapult ships and CAM ships that could carry a single (disposable) fighter. In the interim, before escort carriers could be supplied, they also brought in merchant aircraft carriers that could operate four aircraft.

In 1940, Admiral William Halsey recommended construction of naval auxiliaries for pilot training.[3] In early 1941 the British asked the US to build on their behalf six carriers of an improved Audacity design but the US had already begun their own escort carrier.[4] On 1 February 1941, the United States Chief of Naval Operations gave priority to construction of naval auxiliaries for aircraft transport.[5] U.S. ships built to meet these needs were initially referred to as auxiliary aircraft escort vessels (AVG) in February 1942 and then auxiliary aircraft carrier (ACV) on 5 August 1942.[6] The first U.S. example of the type was USS Long Island. Operation Torch and North Atlantic anti-submarine warfare proved these ships capable aircraft carriers for ship formations moving at the speed of trade or amphibious invasion convoys. U.S. classification revision to escort aircraft carrier (CVE) on 15 July 1943 reflected upgraded status from auxiliary to combatant.[7] They were informally known as "Jeep carriers" or "baby flattops". It was quickly found that the escort carriers had better performance than light carriers, which tended to pitch badly in moderate to high seas. The Commencement Bay class was designed to incorporate the best features of American CVLs on a more stable hull with a less expensive propulsion system.[8]

Among their crews, CVE was sarcastically said to stand for "Combustible, Vulnerable, and Expendable". Magazine protection was minimal in comparison to fleet aircraft carriers.[9] HMS Avenger was sunk within minutes by a single torpedo, and HMS Dasher exploded from undetermined causes with very heavy loss of life. Three escort carriers—USS St. Lo, Ommaney Bay and Bismarck Sea—were destroyed by kamikazes, the largest ships to meet such a fate.

Allied escort carriers were typically around 500 ft (150 m) long, not much more than half the length of the almost 900 ft (270 m) fleet carriers of the same era, but were less than ​¹⁄₃ of the weight. A typical escort carrier displaced about 8,000 long tons (8,100 t), as compared to almost 30,000 long tons (30,000 t) for a full-size fleet carrier. The aircraft hangar typically ran only ​¹⁄₃ of the way under the flight deck and housed a combination of 24–30 fighters and bombers organized into one single "composite squadron". By comparison, a late Essex-class fleet carrier could carry a total of 103 aircraft organized into separate fighter, bomber and torpedo-bomber squadrons.

The island (superstructure) on these ships was small and cramped, and located well forward of the funnels (unlike on a normal-sized carrier, where the funnels were integrated into the island). Although the first escort carriers had only one aircraft elevator, having two elevators (one fore and one aft), along with the single aircraft catapult, quickly became standard. The carriers employed the same system of arresting cables and tail hooks as on the big carriers, and procedures for launch and recovery were the same as well.

The crew size was less than ​¹⁄₃ of that of a large carrier, but this was still a bigger complement than most naval vessels. It was large enough to justify the existence of facilities such as a permanent canteen or snack bar, called a gedunk bar, in addition to the mess. The bar was open for longer hours than the mess and sold several flavors of ice cream, along with cigarettes and other consumables. There were also several vending machines available on board.

In all, 130 Allied escort carriers were launched or converted during the war. Of these, six were British conversions of merchant ships: HMS Audacity, Nairana, Campania, Activity, Pretoria Castle and Vindex. The remaining escort carriers were U.S.-built. Like the British, the first U.S. escort carriers were converted merchant vessels (or in the Sangamon class, converted military oilers). The Bogue-class carriers were based on the hull of the Type C3 cargo ship. The last 69 escort carriers of the Casablanca and Commencement Bay classes were purpose-designed and purpose-built carriers drawing on the experience gained with the previous classes.

Originally developed at the behest of the United Kingdom to operate as part of a North Atlantic convoy escort, rather than as part of a naval strike force, many of the escort carriers produced were assigned to the Royal Navy for the duration of the war under the Lend-Lease act. They supplemented and then replaced the converted merchant aircraft carriers that were put into service by the British and Dutch as an emergency measure until the escort carriers became available. As convoy escorts, they were used by the Royal Navy to provide air scouting, to ward off enemy long-range scouting aircraft and, increasingly, to spot and hunt submarines. Often additional escort carriers also joined convoys, not as fighting ships, but as transporters, ferrying aircraft from the U.S. to Britain. In this case, the aircraft cargo could be doubled by storing aircraft on the flight deck as well as in the hangar.

The ships sent to the Royal Navy were slightly modified, partly to suit the traditions of that service. Among other things the ice cream making machines were removed, since they were considered unnecessary luxuries on ships, which served grog and other alcoholic beverages. The heavy duty washing machines of the laundry room were also removed since "all a British sailor needs to keep clean is a bucket and a bar of soap" (quoted from Warrilow).

Other modifications were due to the need for a completely enclosed hangar when operating in the North Atlantic and in support of the Arctic convoys.

Meanwhile, the U.S. discovered their own use for the escort carriers. In the North Atlantic, they supplemented the escorting destroyers by providing air support for anti-submarine warfare. One of these escort carriers, USS Guadalcanal, was instrumental in the capture of U-505 off North Africa in 1944.

In the Pacific theater, escort carriers lacked the speed to sail with fast carrier attack groups, so were often tasked to escort the landing ships and troop carriers during the island-hopping campaign. In this role they provided air cover for the troopships and flew the first wave of attacks on beach fortifications in amphibious landing operations. On occasion, they even escorted the large carriers, serving as emergency airstrips and providing fighter cover for their larger sisters while these were busy readying or refueling their own planes. They also transported aircraft and spare parts from the U.S. to remote island airstrips.

The attack on Pearl Harbor brought up an urgent need for aircraft carriers, so some T3 tankers were converted to escort carriers, USS Suwannee is example of how a T3 tanker hull AO-33 was rebuilt to be an escort carrier. The T3 tanker size and speed made the T3 a useful escort carrier. There were two classes of T3 hull carriers: Sangamon class and Commencement Bay class.[10][11][12]

Battle off Samar

USS Gambier Bay, burning from earlier gunfire damage, is bracketed by a salvo from a Japanese heavy cruiser (faintly visible in the background, center-right) shortly before sinking during the Battle off Samar.

A major battle for these escort carriers was the Battle off Samar in the Philippines on 25 October 1944. The Japanese lured Admiral William Halsey, Jr. into chasing a decoy fleet with his 3rd Fleet. This left aircraft from 16 small and slow escort carriers in three task groups armed primarily to bomb ground forces; along with their protective screen of destroyers and slower destroyer escorts, with "Taffy 3" bearing the brunt of the fight. They faced a Japanese force of four battleships, including the formidable[13] Yamato, eight cruisers, and 11 destroyers. The American ships held off the Japanese.

The slow carriers could not outrun 30 kn (35 mph; 56 km/h) cruisers. They launched their aircraft and maneuvered to avoid shellfire for over an hour. They took dozens of hits, mostly from armor-piercing rounds that passed right through their thin, unarmored hulls without exploding. USS Gambier Bay, sunk in this action, was the only U.S. carrier lost to enemy surface gunfire in the war, and the Japanese concentration of fire on this one carrier assisted the escape of the others. The carriers′ only substantial armament—aside from their aircraft—was a single 5 in (127 mm) dual-purpose gun mounted on the stern, but the pursuing Japanese cruisers closed to within range of these guns. One of the guns caused critical damage to the burning Japanese heavy cruiser Chōkai and a subsequent bomb dropped from one of the task force's aircraft hit the heavy cruiser's forward machinery room, leaving her dead in the water. Several kamikaze aircraft were shot down by carrier gunners, with only USS St Lo lost to air attack. The Americans lost a similar number of ships and men to the Battle of Coral Sea and Battle of Midway combined.

Model of the Casablanca-class Gambier Bay at USS Midway museum

Many escort carriers were Lend-Leased to the United Kingdom, this list specifies the breakdown in service to each navy.

• Long Island class: Two ships, one in USN service (USS Long Island) and one in British service (HMS Archer).
• Avenger class: Four ships, one mainly in USN service (as USS Charger) and three in British service.
• Sangamon class: Four ships, all in USN service.
• Bogue class: 45 ships, 11 in USN service, 34 in British service as Attacker class (first group) and Ruler class (second group).
• Casablanca class: 50 ships, all in USN service.
• Commencement Bay class: 19 ships, all in USN service, including two that were accepted but not commissioned and laid up for many years after the war. Four more units were canceled and scrapped on the building slips. The Commencement Bay-class ships were seen as the finest escort carriers ever built,[14] and several units continued in service after the war as training carriers, aircraft ferries and other auxiliary uses.

In addition, six escort carriers were produced by the British during the war (all converted from other vessels).

The table below lists escort carriers and similar ships performing the same missions. The first four were built as early fleet aircraft carriers. Merchant aircraft carriers (MAC) carried trade cargo in addition to operating aircraft. Aircraft transports carried larger numbers of planes by eliminating accommodation for operating personnel and storage of fuel and ammunition.

The years following World War II brought many revolutionary new technologies to the navy, most notably the helicopter and the jet fighter, and with this a complete rethinking of its strategies and ships′ tasks. Although several of the latest Commencement Bay-class CVE were deployed as floating airfields during the Korean War, the main reasons for the development of the escort carrier had disappeared or could be dealt with better by newer weapons. The emergence of the helicopter meant that helicopter-deck equipped frigates could now take over the CVE's role in a convoy while also performing their own traditional role as submarine hunters. Ship-mounted guided missile launchers took over much of the aircraft protection role, and in-flight refueling abolished the need for floating stopover points for transport or patrol aircraft. As a result, after the Commencement Bay class, no new escort carriers were designed, and with every downsizing of the navy, the CVEs were the first to be mothballed.

Several escort carriers were pressed back into service during the first years of the Vietnam War because of their ability to carry large numbers of aircraft. Redesignated AKV (air transport auxiliary), they were manned by a civilian crew and used to ferry whole aircraft and spare parts from the U.S. to Army, Air Force and Marine bases in South Vietnam. However, CVEs were useful in this role only for a limited period. Once all major aircraft were equipped with refueling probes, it became much easier to fly the aircraft directly to its base instead of shipping it overseas.

The last chapter in the history of escort carriers consisted of two conversions: As an experiment, USS Thetis Bay was converted from an aircraft carrier into a pure helicopter carrier (CVHA-1) and used by the Marine Corps to carry assault helicopters for the first wave of amphibious warfare operations. Later, Thetis Bay became a full amphibious assault ship (LHP-6). Although in service only from 1955 (the year of her conversion) to 1964, the experience gained in her training exercises greatly influenced the design of today's amphibious assault ships.

In the second conversion, in 1961, USS Gilbert Islands had all her aircraft handling equipment removed and four tall radio antennas installed on her long, flat deck. In lieu of aircraft, the hangar deck now had no fewer than 24 military radio transmitter trucks bolted to its floor. Rechristened USS Annapolis, the ship was used as a communication relay ship and served dutifully through the Vietnam War as a floating radio station, relaying transmissions between the forces on the ground and the command centers back home. Like Thetis Bay, the experience gained before Annapolis was stricken in 1976 helped develop today's purpose-built amphibious command ships of the Blue Ridge class.

Unlike almost all other major classes of ships and patrol boats from World War II, most of which can be found in a museum or port, no escort carrier or American light carrier has survived: all were destroyed during the war or broken up in the following decades. The Dictionary of American Naval Fighting Ships records that the last former escort carrier remaining in naval service — USS Annapolis — was sold for scrapping 19 December 1979. The last American light carrier (the escort carrier's faster sister type) was USS Cabot, which was broken up in 2002 after a decade-long attempt to preserve the vessel.

The U.S. designed the Sea Control Ship[18] to serve a similar role; whilst none were actually built, the Spanish Principe de Asturias and the Thai Chakri Naruebet are based on the concept.

• CAM ship
• Merchant aircraft carrier

For complete lists see:

• List of escort carriers by country
• List of United States Navy escort aircraft carriers
• List of sunken aircraft carriers
• List of escort carriers of the Royal Navy
• List of ships of the Imperial Japanese Navy
• List of aircraft carriers of World War II

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• Gallery, Daniel V. (1965). 20 Million Tons Under The Sea. New York: Ballantine.
• Galuppini, Gino (1981). Le guide des porte-avions. Paris: Fernand Nathan.
• Goldberg, Mark H (1992). 'Caviar & Cargo' The C3 Passenger Ships. North American Maritime Books.
• Hague, Arnold (1998). Convoy Rescue Ships 1940–45. World Ship Society. ISBN 0-905617-88-6.
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• Poolman, Kenneth (1972). Escort Carrier 1941–1945: An Account of British Escort Carriers in Trade Protection. London: Ian Allan.
• Warrilow, Betty (1989). Nabob, the First Canadian-manned Aircraft Carrier. Owen Sound, Ont.: Escort Carriers Association.
• Y'Blood, William T. (1987). The Little Giants: U.S. Escort Carriers Against Japan. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-275-3.

Media related to Escort carriers at Wikimedia Commons

• The Battle Off Samar – Taffy III at Leyte Gulf website by Robert Jon Cox