Like standard stormtroopers, they wore white armor. They were also equipped with breathing tubes that were attached to a scuba backpack to their helmets and had underwater propulsion jets on their backs. They utilized fins on their boots and were equipped with DC-12U beam rifles and used OMS Devilfish subs.
Cadets at the Imperial Naval Academy on Carida also trained as seatroopers.
In 18 BBY, seatroopers participated in the aftermath of the Battle of Dac City on Mon Cala after all surface cities were destroyed along with Imperial forces. While the Imperial Naval Academy of Carida primarily trained Imperial Starfighter Pilots, Imperial cadets also trained for other Imperial units including Seatroopers. On one occasion, Han Solo and his fellow cadets trained in an underwater exercise donning Seatrooper armor.
At one point, a few years prior to the Battle of Yavin, seatroopers on Lothal stood by during an aquatic training exercise for Imperial cadets. During a in the days after the Battle of Endor, stormtroopers on the ice moon Madurs donned underwater armor and engaged in the freezing seas around the . Their armor was sleek and white but did not protect against an summoned by Princess Leia Organa.
The original seatroopers as depicted in Star Wars 74: The Iskalon Effect
Seatroopers first reappeared in canon in Jason Fry's 2015 junior novel Servants of the Empire: Rebel in the Ranks. The seatrooper was first pictured in Darth Vader (2017) 15, a 2018 comic authored by Charles Soule and penciled by Giuseppe Camuncoli.
Seatroopers originally appeared in the 1983 Star Wars Legends comic issue Star Wars (1977) 74.