The TIE Advanced x1, or TIE/x1 was an advanced prototype starfighter touted as a replacement for the standard TIE Fighter tested by Darth Vader and X1 at the battles of Yavin and Mustafar respectively. While it never made it into production, many of its best design features were later incorporated into the TIE/sa bomber and TIE/IN interceptor. In the First War, Cirilla Fiona Elen Riannon lends Darth Vader's TIE/x1 and later used it as their main fighter of choice until it was destroyed in the Great Battle of Endor. Further development of the Advanced continued, eventually leading to the TIE Avenger and TIE Defender. The TIE Advanced x1 featured a Sienar Fleet Systems I-s3a solar ionization reactor and paired P-s5.6 twin ion engines like the original TIE Fighter. However, the x1 had an original spaceframe, with an elongated rear deck and reinforced durasteel-alloy hull. The x1's most important innovation was the use of "bent-wing" solar array wings, like those used on the TIE/sa bomber, which had the advantages of increased surface area for more power while also reducing the craft's profile, compared to the TIE/LN starfighter's hexagonal panel wings.