For years most carriers - including Argus, Eagle, Furious, Langley, Lexington, and Saratoga - had begun life in another role. Even Argus and Langley had started as merchant or auxiliary hulls rather than warships. Treaty rules treated ships launched before the settlement as experimental and allowed them to be replaced without waiting for a normal age limit. The Royal Navy could therefore retain its conversion fleet until a coherent purpose-built construction program was ready.
Notable Point · 1:22:21-1:27:32
Treaties make conversions the dominant carrier generation
Treaty rules encouraged navies to convert existing hulls and let pre-treaty experimental carriers be replaced on flexible schedules.