Battle of the drill

The Battle on the Drill was a battle fought outside the Outer Wall of Ba Sing Se. It was an assault by the Fire Nation using a drill, a massive device solely intended to drill a path through Ba Sing Se's massive walls to allow for a larger invasion. The Drill was destroyed and the Fire Nation thus defeated due to the intervention of Team Avatar.

History
The Mechanist was designing weapons for the Fire Nation, and the Fire Nation created plans for the drill using his information. The Fire Nation began constructing the massive drill it an attempt to break through the outer and inner walls of Ba Sing Se. It was their hope that by clearing a path for their armies, the city would be conquered, finally ending the War in a Fire Nation victory.

The Battle
After completion, the drill and a small force of Fire Nation tanks headed towards the great city to break in. Unfortunately for the Fire Nation, the force arrived at the exact time as Team Avatar and Aang spotted the device.

Ba Sing Se's army was unprepared due to never having fought a major battle in years and their only means of defense were throwing boulders at the Drill, which of course had little success. General Sung who commanded the troops on the Outer Wall, did not see the Drill as a real threat and was confident in the Terra Team, a group of elite Earthbenders. Despite their best efforts, they were however no match for Ty Lee and Mai, who promptly ambushed the soldiers. Ty Lee's chi blocking knocked out the entire team within mere moments. With the team helpless, Sung panicked and wanted Team Avatar's help despite his earlier thoughts of not needing it at all.

The Gang came up with a plan of hitting the Drill's pressure points as Ty Lee had done to defeat the Terra Team. Aang, Katara and Sokka broke into the Drill when Toph tried to slow it down from the outside because she could not sense vibrations within the massive machine. Having stolen a schematic from a Drill worker, the group headed for the front-most part of the Drill where massive metal braces held the entire thing together. Aang and Katara began cutting completely through the braces using waterbending, but found it was too much work to be done before the Drill broke through the wall. Sokka suggested that they didn't need to cut through the braces completely and then Aang could deliver a final blow that would destroy the weakened braces. Meanwhile, the crew found the Drill worker that Katara had frozen earlier, so Azula, Mai and Ty Lee were sent to stop the attack. The Gang fled as they could not fight and cut through the braces at the same time.

Aang eventually separated from Sokka and Katara to deliver the final blow. Katara and Sokka managed to escape the machine from riding slurry (a mixture of water and earth used to deposit the rock from the wall). Ty Lee followed them in the pipe, but Mai did not stating "Azula can shoot all the lightning she wants at me, I'm not going in that wall sludge juice." Because the slurry is water and earth combined, both Katara and Toph were able to bend it from the outside and build up more pressure for when the blow was delivered. Meanwhile, Aang dodged falling boulders from Sungs' men as Sung thought that this would be an effective measure, even though it clearly was not. Aang uses the rock to his advantage and makes a wedge shape that he shoves into the front of the Drill. He then uses airbending to speed-run down the outer wall and lands on the wedge, causing the braces to snap in half and the Drill to collapse in a slurry mess. In the wreckage, Mai humbly says "We lost".

Aftermath
The drill wreckage was not immediately cleaned up or disposed of, but this proved to be a major help for Team Avatar.

At least a month later, the gang used the drill as proof of The War to Earth King Kuei. The Dai Li leader, Long Feng, tried to convince the king that it was "a construction project" but the king didn't believe him. This resulted in Long Feng's arrest.

Appearances

 * The Drill
 * Avatar: The Last Airbender - The Burning Earth (Non-canon)