If a vessel was equipped with a deflector shield, the hull rating was often accompanied by SBD, the deflector shield strength. An Imperial TIE fighter hull was rated at 9 RU. The EF76 Nebulon-B escort frigate had a hull rating of 448 RU and shield-strength rating of 960 SBD.
Behind the scenes
RU was first used in the 1993 LucasArts starfighter simulator Star Wars: X-Wing. It was later defined in The Stele Chronicles, a short booklet included in the package of the LucasArts PC video game Star Wars: TIE Fighter.