The Aquatic Terrain Armored Transport, alternatively known as the AT-AT swimmer, served as a combat vehicle within the Galactic Empire, functioning as the marine counterpart to the terrestrial AT-AT walker. Specially trained personnel known as Imperial Army pilots were responsible for operating these vehicles.
The AT-AT swimmer's production was a collaborative effort between Kuat Drive Yards and Hydrospeare Corporation; it originated from significant modifications made to the standard AT-AT by the Imperial Army garrison stationed on Kabaira.
The command center was connected to a spacious section of the vessel designed for carrying passengers. It was employed in deep-sea operations alongside TIE fighter boats and aquatic assault stormtroopers, and could be located at Imperial aquatic military installations. The Y-85 Titan dropship was also capable of deploying the AT-AT swimmer. It had the capacity to transport 40 soldiers and 600 kilograms of cargo.
Its shell-like plating was engineered to endure and shield the vehicle from the immense pressures found in deep water, the corrosive effects of salt water, and incoming blaster projectiles. The head unit was designed to allow for firing in any direction.
Similar to its land-based equivalent, the AT-AT swimmer was equipped with two enhanced heavy laser cannons. To accommodate the four supplementary repulsorlift engines necessary for buoyancy, its main body was wider than that of the standard AT-AT. These repulsorlift engines generated a substantial field capable of deflecting objects from the craft's lower section, although strong swimmers could penetrate this field where it was weakest.
By the year 137 ABY, the design had undergone substantial alterations. The version used by Darth Krayt's Galactic Empire was capable of underwater operation and possessed shields. It was armed with a minimum of six laser cannons, including a rear-mounted double laser cannon for defense against attacks from behind, and featured a launch bay that could house at least five Shark underwater fighters. Despite being more streamlined, the updated design maintained a visual resemblance to its predecessor. The command bridge was also redesigned to resemble that of a standard AT-AT. Furthermore, these vehicles were known to have transported Sith Lords on several occasions.
The AT-AT Swimmer, born from extensive modifications to the mech by the Imperial Army garrison on Kabaira, laid the groundwork for what would become the Aquatic Terrain Armored Transport. Its subsequent mass production led to deployments on planets like Kaal, where it significantly hindered Rebel operations. This prompted General Carlist Rieekan, upon reviewing the Imperial Military's official field manual, Imperial Handbook: A Commander's Guide, to note the necessity of importing attack submarines from Mon Calamari.
More than a century later, during the Genocide of Mon Calamari on Dac in 137 ABY, at least one modernized AT-AT Swimmer saw action. It served as transport for Darth Azard and Sith scientist Vul Isen to the Soheras Trench. There, Isen had created a Sea Leviathan, which the two then used the Force to awaken and command to massacre Mon Calamari prisoners held at Imperial Extermination Camp 28, and subsequently hunt down and eliminate all Mon Calamari in its path.