"Skirmish in the Sky" (移動要塞エッグフォート襲来!,Idōyōsai Eggu Fōto Shūrai!?, lit. "Raid of Egg Fort, the Flying Fortress!") is the fifteenth episode of the anime series, Sonic X. It first aired on 13 July 2003 and 13 December 2003 in Japan and US respectively.
At the start of the episode, Chris gives Sonic a mobile phone, but he doesn't want it, tosses it to Amy and takes off for a run. While Chris questions why Sonic doesn't want a mobile phone, Tails respond that Sonic wants to be left alone. When Chris points out that the city might be in danger caused by Doctor Eggman, Tails notes that Sonic will appear when that time comes. Ella, Tails, Amy, Cream and Cheese plan to go shopping because they no longer need to hide in public although wherever the group goes there are people who always seem to stare at them almost all the time, much to their dismay. Meanwhile, while there are construction workers extracting the remains of Dr. Eggman's former base, Eggman launces a battleship called the Egg Fort, surprising the workers as it takes off to the skies. Once it hovers past Station Square, the doctor deploys numerous "E-42 Torole" robots from below and proceeds to destroy Station Square and renovate it into the doctor's favourable Eggmanland as revenge from the destruction of Eggman's base. Sonic arrives into the scenery, destroys the robots and tries to battle Eggman, but he fails to reach the Egg Fort. Tails discovers the only way to defeat Eggman is by using the X-Tornado, which is still at Chris's home. Sam Speed arrives and takes Tails, Amy, Cream, Chris and Ella home.
At the same time, Sonic is attacked by Eggman's E-43 Falcons but he rides on one in attempt to reach the Egg Fort. Despite of this, Eggman activates the flying robots' self-destruct ability and barely hangs on to the Egg Fort which makes an annoying screeching sound. Eventually Sonic loses his grip and has to drop off the flying battleship. Sonic then gets attacked by another type of robot named "E-33 Buball". Tails, Amy, Cream, Chris, Ella and Sam are attacked by the said robot, but Mr. Stewart saves them with a mirror to reflect the lasers to destroy them. He joins with the gang. The robots attack again, but Tanaka saves them in a futuristic big rig truck with the X-Tornado. Tails, Amy and Chris then use the plane and take off to the skies to stop Eggman as Sonic joins along.
The X-Tornado then takes the fight out over the ocean to prevent further damage to Station Square. Sonic taunts at Eggman so they can get his attention and follow the heroes towards the ocean. Despite that the plane gets shot by one of the Egg Fort's weapons, Sonic defeats the battleship by using 2 Power Rings at once. The Egg Fort sinks below the ocean, but Sonic, Tails, Amy and Chris are worried Eggman will soon be back.