The steam catapult was a British invention. Up to and during World War II most catapults were hydraulic, and there were a number of armed merchantmen, known as CAM ships ("catapult armed merchantmen"), that had rocket-driven catapults. Some carriers were completed before and during World War II with catapults on the hangar deck that fired athwartships, but they were unpopular due to their short run, low clearance of the hangar decks, inability to add the ship's forward speed to the aircraft's airspeed for takeoff, and lower clearance from the water (conditions which afforded pilots far less margin for error in the first moments of flight). They were mostly used for experimental purposes, and their use was entirely discontinued during the latter half of the war.

from: http://en.wikipedia.org/wiki/Aircraft_catapult

17 FEB 42--The Commander in Chief, U.S. Fleet authorized removal of athwartships hangar deck catapults from Wasp, Yorktown, Enterprise, and Hornet.