The Royal Escort Group was a fleet of airships used by the Fire Nation Royal Family. The fleet was technically part of the Fire Nation Air Force. The Royal Escort was also used for bombarding the city of Shu Shin She.
After the battle, the fleet was hijacked by Earthbenders. They didn't have enough people to crew the ships, so some of the airships were taken to attack them by the Fire Nation. The Earthbenders used their airships to destroy the others.