Hiroshi's secret airfield

The Equalist airfield was the base of operations for Hiroshi Sato's biplane armada during the battle against the United Forces.

History
After the United Forces entered Republic City's harbor, they quickly found themselves being ambushed by a fleet of Equalist biplanes that had been deployed from an airfield located in the mountains north-west of the city.

Later on, Team Avatar, along with the newly recruited General Iroh, pinpointed the airfield's location on a map of Republic City and its surrounding areas. Iroh, Bolin, and Asami then decided that at dawn, they were going to travel to the airfield and stop any more aircraft from taking off, while Korra and Mako went to find and confront Amon.

The next day, as the group approached the airfield, Bolin instructed Naga and Pabu to stay behind, and not to follow them into the base. As they approached the compound, they were electrocuted by an invisible fence, and brought to a prison cell in the building. After being visited by Hiroshi Sato, who told them that he was about to destroy Bumi's battleship fleet, Naga and Pabu broke into the airfield base and broke the iron bars that were holding Iroh, Bolin, and Asami prisoner. Bolin then rhetorically stated "who needs metalbenders? We've got Naga!" The group then proceeded to head outside, towards the individual airstrips.

Once outside, General Iroh managed to commandeer a biplane that was about to take off, and went after the armada that was headed towards Commander Bumi's fleet of battleships. Meanwhile, Asami discovered a number of mecha tanks and biplanes in the airfield's hanger, and seized control of one, using it to destroy the biplanes in the hanger. Meanwhile, Bolin was outside, using his earthbending to destroy the airstrips, effectively preventing any more biplanes from taking off. Back inside the hanger, however, as Asami was using her mecha tank to destroy more Equalist biplanes, she was approached by her father, who was also in a mecha tank. After a brief fight, Hiroshi was about to deliver the final blow, but was stopped by Bolin, who launched an enslaught of earthbending attacks at him. Hiroshi was eventually captured, and the airfield was effectively taken out.

Design
The Equalist's airfield consisted of a large hanger, for storing biplanes and mecha tanks, as well as at least one prison cell, and a number of individual airstrips.