The Queen Elizabeth-class carriers were not originally intended to use steam catapults. Their gas-turbine machinery does not provide the steam plant that such a launch system would need. Converting them would require substantial steam generation and new piping through a hull that was never arranged for it. The design did reserve space for electrical cabling, making an electromagnetic launch system a structurally different proposition.
Notable Point · 1:26:37-1:27:00
Why steam catapults did not fit the Queen Elizabeth design
The carriers' gas-turbine architecture reserved routes for electrical launch equipment, while a steam catapult would have required a different generation and piping system.