The Thalmussen was a Wookiee vessel of the transport type, originating from the planet of Kashyyyk, the homeworld of their species. This starship possessed a grey hull adorned with a pair of orange stripes across its middle section, and it was powered by two engines. Sometime in the period spanning from 39 BBY to 36 BBY, the Thalmussen, accompanied by three other ships of the same design, participated in the transportation of some of the initial Wookiee settlers to the moon known as Alaris Prime.
Navigating through the Alaris Expanse, a region of space, the ship journeyed in formation with the other vessels until they reached their destination on the moon, touching down in a clearing situated near a large water source. While the majority of the Wookiees remained aboard the transport ships, Chewbacca, Shoran and Attichitcuk ventured forth to scout the surrounding area.
The video game Star Wars: Galactic Battlegrounds, developed by LucasArts in 2001, marked the initial appearance of the Thalmussen. The name of the Thalmussen is only mentioned within the Wookiee tutorial campaign's description. It is also visible in the introduction of the first level of the campaign, entitled "Moving and Attacking". During the level itself, four transport ships of identical design are depicted; however, the specific identity of the Thalmussen among them is not explicitly revealed.