The Sealion, a Missile Boat prototype, was delivered to the Rebel Alliance as a test model.
This Missile Boat prototype, known as the Sealion, was commandeered by forces serving the rogue Grand Admiral Zaarin. During a meeting with his officers, Zaarin revealed that the Rebels were heading into a trap at Endor concerning the second Death Star, but he chose not to warn them. Namuura Din, a loyal commander in charge of the Victory-class Star Destroyer Zeplin, decided to relay this information, along with the Sealion, to the Alliance and defected. Although Zaarin couldn't prevent his departure, Loyalist forces, under the command of Darth Vader aboard the Imperial-class Star Destroyer Garrett, intercepted and captured Din's flagship. However, the Sealion had already been transferred to the Mon Calamari Cruiser Link, which then jumped to lightspeed.
The Link's commanding officer attempted to transmit the intelligence to Rebel Command, but the ship's engines malfunctioned, prematurely pulling it out of Hyperspace. Consequently, the Link's commander dispatched the Sealion to a Rebel stronghold, the XQ4 Platform Enin'sd, for detailed analysis. However, before the Rebels could dismantle the vessel and uncover its secrets, Imperial forces arrived at the base, intending to either destroy or covertly recover the Sealion. The Prophets of the Dark Side ultimately recovered it before its container was destroyed, thus preventing the Rebels from producing their own Missile Boats. Nevertheless, the Rebel's capture of the Sealion, coupled with the destruction of the Missile Boat production facilities via planetary bombardment by Grand Admiral Zaarin's breakaway faction's, resulted in Emperor Palpatine's order to suspend all Missile Boats from service indefinitely, with the remaining vessels placed in secure storage.
The Sealion makes its sole appearance in Battle 13 Combat 4 of Star Wars: TIE Fighter. The initial mission involving the prototype depicts the ship on the Link, while the final mission focuses on the fighter being hidden within a Class-B cargo container group called Niicee.
There are two ways to deal with the Sealion. The primary objective involves destroying the container, thus eliminating the Sealion. The secondary objective requires recapturing the Sealion at the Rebel Base it flees to. The player must identify the correct container and allow a cargo ferry to retrieve it.