The shaft-driven lift fan propulsion system that will enable the Lockheed Martin F-35B Lightning II stealth fighter to perform short takeoffs and vertical landings (STOVL) operated for the first time in the aircraft during ground testing on Sunday, May 25. At full power, the F-35B's system generates more than 40,000 pounds of lifting force, or about 170 percent more than current-generation STOVL fighters.