"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 waterbending powered submarines are naval vehicles designed by Sokka of the Southern Water Tribe and built by the mechanist. These vehicles were utilized in the invasion of the Fire Nation, and were used to transport Earth Kingdom and Water Tribe soldiers and benders into the harbor of the Fire Nation Capital.
After Ba Sing Se fell to the Fire Nation, Sokka made plans for the invasion of the Fire Nation on the long-awaited Day of Black Sun. Vehicles were needed to transport the invaders into the Fire Nation, so Sokka personally designed submarines, and presented his plans to the mechanist. Despite facing initial difficulty in interpreting Sokka's plans, he figured them out and manufactured the subs for usage by the invasion force.
On the Day of Black Sun, these subs were deployed by Water Tribe boats after the boats were seized by firebenders. The subs navigated past the Great Gates of Azulon, and then proceeded toward the Fire Nation Capital. The subs carried the entire invasion force toward the city, while Aang flew there alone to face the Fire Lord. Once they arrived on shore, the subs released the tanks and the invaders who stormed the Royal Plaza. The subs were defended by Tho, Due, and Huu, waterbenders of the Foggy Swamp Tribe. They stayed behind on the shores, while the invaders proceeded onward.
After the eclipse ended, the Fire Nation drove back the invaders with their air force. They then advanced toward the shore to destroy the subs, thereby trapping the invaders. Huu, Tho and Due did their best to destroy the bombs dropped by the airships, but they were overwhelmed, and all of the subs 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, at least one earthbending-powered tank, and are armed with ice torpedoes. Each submarine has a periscope that is long enough to sprout above water while the ship is submerged. The back of the ship has fins that move when being used.
The plated vessels are overall fairly well-armored, 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 docked on dry land. There are also doors on top of the vessel, allowing troops to walk atop of the ship when moving through water.
The only major weakness 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.
- ↑ 1.0 1.1 1.2 1.3 1.4 "The Day of Black Sun, Part 1: The Invasion". Michael Dante DiMartino (writer) & Giancarlo Volpe (director). Avatar: The Last Airbender. Nickelodeon. November 30, 2007. No. 10, Book Three: Fire
- ↑ 2.0 2.1 From older Avatar: The Last Airbender official site, originally on Nick.com (link). No longer updated.
- ↑ "The Crossroads of Destiny". Aaron Ehasz (writer) & Michael Dante DiMartino (director). Avatar: The Last Airbender. Nickelodeon. December 1, 2006. No. 20, Book Two: Earth
- ↑ "The Day of Black Sun, Part 2: The Eclipse". Aaron Ehasz (writer) & Joaquim Dos Santos (director). Avatar: The Last Airbender. Nickelodeon. November 30, 2007. No. 11, Book Three: Fire