Lex (cv-2)
LEX (CV-2) and her sister, USS SARATOGA (CV-3) were sister ships, originally laid down as Cruisers but finished as our first Aircraft Carriers as the result on the Washington Conference on Arms Limitations after WWI.
Yes - USS LANGLEY was CV-1, but was never carried on the Naval Register as a combatant - she had no combat capability such as magazines, armament, speed, etc.
Both CV-2 and CV-3 were unique in being powered by steam generated electricity to power turbo-electric drive. However, it was so complex, heavy and expensive that later Carriers used traditional closed loop steam, reduction geared turbine propulsion.
The later ESSEX Class USS LEXINGTON was CV-16 originally, eventually became AVT-16 as a training Carrier stationed in the Gulf of Mexico at Pensacola for the Naval Air Training Command.