If I recall correctly, the catapult wasn't actually used all that often on the Essex class carriers. During WWII catapults were Hydraulic and the aircraft weren't designed for them, requiring a cradle to be attached to the aircraft.
Which would have to be caught after take-off. The process to launch all... what? 80 Aircraft with two catapults... would take forever and wouldn't be worth the security of knowing you'll reach flight speed.
Especially since all carrier borne aircraft of the period could take off on the runway space of a carrier deck, and with the ship steaming at 20-30 knots into the wind... Takeoff was easy for large numbers of aircraft without catapults.
Once Jet aircraft really hit the scene in the 50's is was necessary to adapt catapults as jets take alot more room to take off than prop driven aircraft.
It was some British guy who came up with steam driven catapults and in the late 50's most of the Essex class carriers were refitted with them, along with an added runway for landing/takeoff that angled off to port.
