On 15 November 1934, the Bureau of Naval Aeronautics established plans to install hydraulic, flush-deck catapults on the USS Yorktown (CV-5) and USS Enterprise (CV-6). The Type H, Mark I catapult was manufactured by the Naval Aircraft Factory in Philadelphia, Pennsylvania and was the first to be enclosed under the surface of the carrier flight deck.
Hydraulic catapults would serve Naval Aviation from the 1930's until the 1970's. Aircraft would be attached to the catapults via a bridle system hooked on attachment hooks underneath the aircraft to the shuttle of the catapult as seen below.
Tour the catapult machinery room on the USS Yorktown (CV-10) via You Tube...