They're making a propulsion system that burns hotter to increase efficiency, which means more power, longer range, and reduced CO2 emissions.
This is the Dreadful U.S Air Force Aircraft: https://youtu.be/0SQ0hf2R3BU
Team Tempest revealed that they are currently developing some very innovative technology that will be used by Britain's Royal Air Force by the year 2035.
Although little is said about what technology Rolls is developing, it's safe to say that the tech will be even more impressive than their 2,000 hp yacht engine.