Shield X: an experimental deflector shield generator of Imperial design, provided nearly complete protection from typical assaults for any starship it powered.
During the Galactic Civil War, the Alliance to Restore the Republic managed to steal it. It was installed on the CR90 corvette called Blade 5 (which was subsequently seized and renamed Ram's Head), and employed in Operation Ram's Head. There are no known records of it being used after that.
The Empire later tried to reproduce this technology at a clandestine space facility. A Rebel B-wing squadron obliterated the base, allegedly terminating the project permanently.