In the ten years following World War II the US Navy's aircraft carrier fleet consisted of ships of the Essex Class (which fought in that war) and ships of the Midway Class (which were built during WW2 but not commissioned until between September 1945 and October 1947).
As jet aircraft became available to the fleet in the early 1950's (including the Korean War) the Navy realized that it would need larger carriers of a fundamentally different design to handle the requirements of launching and recovering large numbers of jet fighters and attack aircraft.
The new carrier's design requirements (incorporated into the Forrestal class) included steam catapults, a larger flight deck and a bigger hangar bay, both to support more numerous and more operationally powerful aircraft. A key feature of the larger flight deck was the inclusion of the angle deck, allowing for simultaneous launching and recovery operations. The Forrestal class was the first class of carrier that included the angle deck as part of its original design. These features plus the huge size of the Forrestal class gave them the unofficial designation of "Super Carrier."