The Egg Fort was a flying fortress used by Dr. Eggman.
The Egg Fort is purple in color, designed with a trio of massive drills, one on the prow and two on the wings. A retractable bridge and three gigantic rocket engines added to this ship's appearance. Armed with a battery of flak cannons and missile launchers, the Egg Fort also carries a pair of high-powered Egg Blasters, which in it's initial usage nearly destroyed the X-Tornado outright.
Eggman constructed the Egg Fort under his original base, expecting the President to order an attack to destroy it. When Rouge, Knuckles and Topaz did infiltrate the facility, leaving it to explode, he boarded it and used it in episode 15 to attack Station Square. However, Sonic destroyed it.
He later repaire it and used it again in the three more episodes, but it was again no match for Sonic and his friends. In "Cruise Blues", Eggman abandoned it in favor for the Egg Fort II when it could not function. The remains of the Egg Fort was salvaged by GUN much later in the series and reconstructed into the Gun Fort, which was pitted against Eggman. However, it was destroyed and either recovered or rebuilt into the Grand Egg Imperial.