|"It was your idea to use waterbending to make the subs sink and float, brilliant! Though your original designs were a bit difficult to decipher. Unfortunately there is one problem I couldn't fix. The subs have a limited air supply."|
|— The mechanist to Sokka.|
The waterbending-powered submarines are naval vehicles designed by Sokka and built by the mechanist. These vessels were used during the invasion of the Fire Nation to transport Earth Kingdom and Water Tribe soldiers and benders as well as vehicles and equipment into the harbor of the Fire Nation Capital.
After Ba Sing Se fell to the Fire Nation, Sokka continued to make plans for an invasion of the Fire Nation on the long-awaited Day of Black Sun, albeit on a smaller scale than initially intended. Vehicles were needed to transport the invaders into the Fire Nation, so he personally designed submarines and presented his plans to the mechanist. Despite facing initial difficulty in interpreting Sokka's plans, the mechanist figured them out and manufactured the submarines for usage by the invasion force.
On the Day of Black Sun, five waterbending-powered submarines were deployed by Water Tribe boats right before the boats were seized by firebenders. The submarines navigated past the Great Gates of Azulon and proceeded toward the Fire Nation Capital. Since the submarines only had a limited supply of air, they had to resurface once before reaching the Fire Nation harbor. Before reaching the shore, the submarines were easy targets for the Fire Nation defenses and multiple battlements shot harpoons at the vehicles with their ballistae. One of the submarines was hit by the projectile and, although a waterbender from the Foggy Swamp Tribe was able to freeze the hole in the vehicle, limiting the damage, the submarine was pulled out of the water. However, before it was left to the mercy of the defenders, Katara used waterbending to cut the metal chain reeling in the vehicle, causing it to drop back into the water and continue its journey to the shore.
In order to gain access to the dock, ice torpedoes were launched from the submarines to blast through the metal bars that were to prevent an underwater attack. Once they arrived on shore, the submarines released the earthbending-powered tanks, the invasion force, and the Earth Kingdom supply trucks, who stormed the Royal Plaza while the submarines were defended by Tho, Due, and Huu.
After the eclipse ended, the Fire Nation drove back the invaders with their air force and quickly advanced toward the shore to destroy the submarines, thereby trapping the invaders. Huu, Tho, and Due did their best to destroy the bombs dropped by the Fire Nation airships, but they were overwhelmed, and all of the submarines were destroyed. Aang and the younger combatants managed to escape on Appa, while the elders were captured.
The vessels are propelled by waterbending, and appear to be fairly large crafts. They can each hold dozens of warriors and at least one earthbending-powered tank and two Earth Kingdom supply trucks. The vessels are armed with ice torpedoes. Each submarine has multiple windows, a periscope at the top of the roof, and three fins, one at the back of the submarine and one fin on each side, that help the submarine to maneuver.
The plated vessels are fairly well-armored overall, as they were able to withstand heavy fire from guard towers, and there are armored plates at the front that can move aside to allow troops and tanks to enter and exit while the sub is on dry land. There are also doors on top of the vessel, allowing troops to walk atop the ship when it is moving through the water.
The only major flaw in the submarines is their inability to store oxygen. Each vessel can only stay underwater for an hour or so at any given time before it must resurface to prevent the passengers from suffocating. This is sufficient when planned for, but limits their underwater range.
- After the Hundred Year War, the Fire Nation engineered submarines based on Sokka's schematics to include in their military arsenal. Zuko and his family used one as a means of entering the Fire Nation capital undetected.
- DiMartino, Michael Dante (writer) & Volpe, Giancarlo (director). (November 30, 2007). "The Day of Black Sun, Part 1: The Invasion". Avatar: The Last Airbender. Season 3. Episode 10. Nickelodeon.
- From older Avatar: The Last Airbender official site, originally on Nick.com. Encyclopedia now broken, archived at The Lost Lore of Avatar Aang - Gear: Waterbending-Powered Submarines.
- Ehasz, Aaron (writer) & DiMartino, Michael Dante (director). (December 1, 2006). "The Crossroads of Destiny". Avatar: The Last Airbender. Season 2. Episode 20. Nickelodeon.
- Ehasz, Aaron (writer) & Dos Santos, Joaquim (director). (November 30, 2007). "The Day of Black Sun, Part 2: The Eclipse". Avatar: The Last Airbender. Season 3. Episode 11. Nickelodeon.
- DiMartino, Michael Dante; Konietzko, Bryan; Yang, Gene Luen (writer), Sasaki of Gurihiru (penciling, inking), Kawano of Gurihiru (colorist), Heisler, Michael; Comicraft (letterer). Smoke and Shadow Part One (September 23, 2015), Dark Horse Comics.