Lightly armored, slower than the fleet carriers and with far less defensive armament and aircraft, yet in great need early, escort carriers were quickly converted from existing merchant, oiler, and cruiser hulls. Initially APV then changed to AVG on 31Mar41, which was changed to ACV on 20Aug42, and all changed to CVE on 15July43.
The experimental escort carriers were merchant hulls with a wooden deck slapped on top. Long Island took less than 90 days to convert. This was an expedient that seemed to work The original designation was AVG-1 indicating auxiliary aircraft ferry. Recall that Wasp, a USN fleet carrier was used, TWICE, to ferry Spitfires to Malta -- a decidedly poor use of a full-blown carriers. So, ten were built for the British who needed help in a hurry: HMS Archer (BAVG-1) class. December 1941, 24 merchant hulls were ordered acquired for conversion, only twenty were available and used ten for each country. Long Island was intended for test and training, but was pressed into fleet service and sailed with the San Diego battleships as backup to the Battle of Midway in case the Japs had broken through Nimitz's famous risk. Fortunately Fletcher won another one. Then L.I. delivered the first aircraft to Guadalcanal and helped win that famous battle.
Immediately after starting on the merchant conversions, four tankers, longer and wider, were made into carriers (reducing the USN tanker fleet at the same time U-boats were doing the same thing). Designation was changed to ACV, auxiliary carriers. These supported the invasion of North Africa and by the end of the year, three headed to the Pacific and one to S. Atlantic. Obviously these larger decks were preferred. Meanwhile H.J.Kaiser promised and succeeded in building 50 new carriers on the Long Island model, merchant hulls with flight decks, within one year. And he did it using mass production techniques with 23 going to the British. Most were used to ferry replacement aircraft across the two oceans -- we won that war by overwhelming the (initially) better trained pilots and superior aircraft of the enemy with industrial production and massive training programs.. Several were used in anti-submarine rolls to good success. Designation was changed to CVE, indicating combat worthy escorts carriers. ( The "CV" is a carryover from Cruiser as carriers originally carried guns and biplanes to extend the cruiser's scouting role. "V" is navy-speak for aircraft.)
In parallel, nine cruiser hulls abuilding were converted to Light Carriers, the Independence class. These had the giant engines of warships giving speed to accompany the Fast Carrier Task Forces in the Pacific.
In practice the larger, tanker-based escort carriers were preferred for near combat conditions. Thus while Kaiser was building his, bigger escort carriers were designed, the Commencement Bay class. Only a few were completed during the war. While the cruiser-based light carriers were holding the line in the Pacific, a larger fleet carrier was also designed, the Midway's, but they were never finished in time to see that war, but fought in Korea and Vietnam. Seventy-seven escort carriers were built during the war and several completed after. New escort carriers were mostly assigned to the Atlantic as anti-sub escorts; the large tanker-conversion carriers saw Atlantic service through the invasion of North Africa in October then joined the Pacific fleet in early 1943. Many CVEs served in the later Pacific years, in addition to convoy escort, as ferries for replenishment aircraft and pilots.Reader Question. The Commencement Bay's were an eigth longer than the Casablanca's, but displaced almost half again. Why?
Long Island 363 ft, 17.6 kt, 13,500 tons Casablanca 515 19.3 7,800 Sangamon 553 18.3 12,000 Independence 619 31.0 11,000 Commencement Bay557 19.0 11,370Size and weight numbers are awkward. There is ship length and beam (several measures (waterline, centerline, dry or full, etc.) and deck length, displacement weight may be dry or loaded that be almost 100% different. In general, Long Island flight decks did not run the length of the ship and she had diesel engines, Casablanca had different engines, and added a catapult. Although beam is similar, length, draft, and weight are much larger on the Commencement Bay's indicating heavier construction. Note that five Casablanca's went down and no Bays. Bays had 2- 5" guns, Blanca's only one. Two catapults vs. one. We can suspect most other combat things were doubled.