In the year 18 BBY, following the Battle of Dac City which took place on Mon Cala, the Galactic Empire deployed a specific kind of underwater vessel to extract Darth Vader from the deep waters of the Great Ungeness Trench. Numerous Imperial underwater vessels engaged in combat with the Mon Cala Mercantile Fleet, commanded by Admiral Raddus, within Mon Cala's southern polar region.
The unnamed submarine made its first appearance in Darth Vader (2017) 15, a canon comic book authored by Charles Soule with illustrations by Giuseppe Camuncoli, which was published in 2018.
The underwater vessel was also featured in Star Wars Legends, specifically in the Star Wars: Rogue Squadron III: Rebel Strike video game from 2003.