Fire Nation drill

Originally designed by The Mechanist at the Northern Air Temple, this metal drill was created for the sole purpose of penetrating Ba Sing Se. It took Fire Nation laborers over two years to construct.

The drill is larger than some villages. It's so big that it actually houses an entire brigade of Fire Nation engineers, who are needed to make repairs and clean out the pipelines. Several metal support beams connect the protective outer shell of the drill to its engine inside. As the drill digs into an earthen structure, the rock is chewed up and turned into slurry a disgusting mixture of rock and water that is dispensed into pipes and dumped out of the rear of the drill.