Notice the two catapult tracks on the flight deck of USS Enterprise.
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.
Aircraft hook up to catapult via a bridle (Different size for each model of aircraft).
Cover to the H-8 model hydraulic catapult manual, this type was installed on the USS Yorktown (CV-10) in 1955.
Diagram of the H-8 catapult
Tour the catapult machinery room on the USS Yorktown (CV-10) via You Tube…
Hydraulics would be replaced by steam catapults, but the next generation of catapults on our aircraft carriers will be Electromagnetic Aircraft Launch System or EMALS.
EMALS reduces stress on airframes because they can be accelerated more gradually to takeoff speed than steam-powered catapults. EMALS also uses less fresh water, reducing the need for energy-intensive desalination. Compared to steam catapults, EMALS weighs less, occupies less space, requires less maintenance and manpower, is more reliable, and uses less energy. Steam catapults, which use about 614 kilograms of steam per launch, have extensive mechanical, pneumatic, and hydraulic subsystems. EMALS uses no steam, which makes it suitable for the Navy's planned all-electric ships. The EMALS could be more easily incorporated into a ramp, which would reduce the aircraft's takeoff speed and consequently the launch energy required. Compared to steam catapults, EMALS can control the launch performance with greater precision, allowing it to launch more kinds of aircraft, from heavy fighter jets to light unmanned aircraft. EMALS can also deliver 122 megajoules of energy, 29 percent more than steam's approximately 95 megajoules. The EMALS will be more efficient than the 5-percent efficient steam catapults. Watch the launch of aircraft via EMALS below.