These opt's where created for the X-Wing Alliance Upgrade project in a attempt to visually enhance the craft in the X-Wing: Alliance game.
Though you can download them here, you can also download them from XWAUP.

Sienar Fleet Systems Lambda-Class Shuttle

The Lambda-class shuttle is a cargo and passenger shuttle that was used by the Imperial fleet. The vessel has a stationary top wing and two folding bottom wings. In flight, the Lambda resembles an inverted "Y", and two lower wings fold up when the craft lands.

Lambda-class shuttles were originally designed by Sienar Fleet Systems. Sienar manufactures the shuttles, while Cygnus Spaceworks is subcontracted to manufacture a more heavily armed version of the ship. Cygnus recently has begun producing more lightly armed shuttles that are virtually identical to the Sienar model.

The Lambda has a heavily reinforced hull and multiple shield generators. The Sienar shuttle has three double laser cannons (one rear mounted) and two double laser cannons.

The Rebel Alliance used the stolen shuttle Tydirium to deliver a commando assault team to Endor's Forest moon. Using appropriated Imperial Command codes purchased from spies and a cover story claiming that they where delivering parts and technical crew, the Rebel team was led by General Han Solo, Princess Leia Organa, and Luke Skywalker managed to infiltrate the Imperial base on Endor and eventually to destroy the Shield protecting the unfinished second Death Star.