The US initially created Escort carriers out of unfinished merchant vessels .
Of these , six ( HMS Nairana , HMS Campania , HMS Activity , HMS Pretoria Castle , HMS Vindex , and HMS Audacity ) were British conversions of merchant ships , the rest being new construction in the USA.Following the war , this class of ship was retired , primarily because as the navies were reduced in size it was better to keep the larger and more useful fleet carriers in preference to them .
Escort carrier