Seatroopers were a specialized division within the Galactic Empire's Stormtrooper Corps, specifically stormtroopers trained for aquatic operations. To facilitate their underwater missions, they utilized specialized gear like scuba gear, underwater propulsion systems, and swim fins. These troopers participated in combat during 18 BBY on the planet Mon Cala. Additionally, some seatrooper units were stationed on Lothal.
Similar to regular stormtroopers, they wore white armor. Their equipment also included breathing apparatuses connected to a scuba unit attached to their helmets, as well as underwater propulsion jets mounted on their backs. They used flippers on their boots and were armed with DC-12U beam rifles and OMS Devilfish subs.
Seatroopers were involved in the aftermath of the Battle of Dac City on Mon Cala in 18 BBY, which occurred after the destruction of all surface cities and the defeat of Imperial forces. Although the Imperial Naval Academy on Carida primarily focused on training Imperial Starfighter Pilots, Imperial cadets also received training for other Imperial units, including Seatroopers. On one occasion, Han Solo, along with his fellow cadets, participated in an underwater training exercise while wearing Seatrooper armor.
Sometime before the Battle of Yavin, seatroopers on Lothal were present during an aquatic training exercise for Imperial cadets. Following the Battle of Endor, stormtroopers on the ice moon Madurs donned underwater armor and engaged insurgent fighters in the frozen seas surrounding the black tower. Despite their streamlined white armor, they were vulnerable to an edont summoned by Princess Leia Organa.
Seatroopers were reintroduced into canon in Jason Fry's 2015 young adult novel, Servants of the Empire: Rebel in the Ranks. The seatrooper made its visual debut in Darth Vader (2017) 15, a 2018 comic book written by Charles Soule and illustrated by Giuseppe Camuncoli.
The initial appearance of seatroopers was in the 1983 Star Wars Legends comic book Star Wars (1977) 74.