Prison rig

The prison rig was an offshore prison for earthbenders where they were forced to build and repair Fire Navy ships. Most of the earthbenders on the rig were captured from the Fire Nation's occupied villages in the Earth Kingdom, where any resistance immediately earned them indefinite imprisonment on the rig. It was run by its cruel and decisive warden. An enormous wall bisects the structure. On one side was a shipyard where the Fire Nation repaired and refueled its ships, and on the other side was a prison for the captive earthbenders. The prisoners were not able to bend because the metal rig was surrounded by water, and they were miles away from land. In addition to this, at the time of the prison rig's creation, the art of metalbending was not yet discovered or taught.

History
Located off the shores of the western Earth Kingdom, which was thoroughly conquered by the Fire Nation, it built many ships for the expansive Fire Navy, and imprisoned hundreds of earthbenders. Any Earth Kingdom citizens who were caught earthbending, which was against Fire Nation law, were considered a threat to the occupation and subsequently sent to the prison rig to silence their bending.

Many prominent earthbenders from the mining village were sent to this rig, including Haru's father, Tyro.

When Haru, an earthbender, was imprisoned and taken to the prison rig, Katara tricked the local authorities into arresting her by pretending to earthbend, in an attempt to locate and save Haru. In the prison, she tried to encourage the earthbenders to fight back and regain their freedom, but they had lost hope and decided not to fight the guards.

Team Avatar came to rescue Katara, but she refused to leave until the other prisoners left too. Opting to help the prisoners, Sokka devised a plan to make use of their airbending companion. Aang blocked up all the air vents except one, went into the boiler room and pushed the coal up with his airbending, releasing it to the only available air vent where the earthbenders were gathered. Katara then urged the earthbender prisoners to fight. At first, the earthbenders declined again, their spirits still broken. Suddenly, Haru threw some coal at the warden, who soon tried to attack Haru with fire, but was blocked by Tyro and three other earthbenders. The rest of the prisoners soon attacked the guards, pushing them back. Finally, the earthbenders threw the firebenders into the ocean. After the victory, the earthbenders used the stolen ships to return to their homeland, swearing to retake their villages from the Fire Nation invaders.

During the battle on the rig, Katara lost her necklace and could not return to retrieve it. It was later found by Prince Zuko, who used the necklace to track down Katara and, subsequently, Avatar Aang.