 | |
| Series | Sonic Underground (DiC, 1999) |
| Season | Season 1 (the only season) |
| Episode | Episode 25 of 40 (production order) · production no. 425 · WildBrain no. 125 |
| French title | La forteresse volante |
| First aired (France) | 31 March 1999 · TF1 |
| First aired (US) | 1 October 1999 · BKN Kids II (syndication) · 25th in US broadcast order |
| Written by | Mark Edens |
| Directed by | Marc Boreal, François Hemmen and Daniel Sarriet; Tom Smith (US) |
| Song | “No One Is an Island” |
| Story arc | Chaos Emerald trilogy, part 1 of 3 (continues in No Hedgehog Is an Island, then New Echidna in Town) |
| Previous episode | Six Is a Crowd (S01E24) |
| Next episode | Beginnings (S01E26) |
Chaos Emerald trilogy 1/3KnucklesThe Flying Fortress
Flying Fortress is episode 25 of Sonic Underground, DiC’s 1999 cartoon about Sonic, Sonia and Manic, the hedgehog triplets of Queen Aleena. It is number 25 in production order – the order TF1 first showed the series in France, where it premiered on 31 March 1999 – and it was the 25th episode to air in the United States, on 1 October 1999. It was written by Mark Edens, and its song is “No One Is an Island”.
Synopsis
A holiday is cut short when Robotnik unveils his newest weapon, a Flying Fortress that can lay waste to Mobius from the sky. Sonic gets on board and tries to bring it down by pulling out its reactor, without success.
Suspecting that the fortress is powered by a Chaos Emerald, Sonic heads for the Floating Island to ask Knuckles for help. The guardian agrees, despite his fear of leaving his island unprotected, and together they hunt through the fortress for its power source.
Sleet and Dingo get there first and make off with the Emerald, and without it the fortress drops out of the sky into the sea, with the heroes still on board. The story continues in No Hedgehog Is an Island.
The Song: “No One Is an Island”
“No One Is an Island” sets up the theme of the three-part story: Knuckles, the loner guardian, cannot save his world on his own.
Key Moments
- Robotnik launches his Flying Fortress.
- Knuckles leaves the Floating Island to help Sonic.
- Sleet and Dingo steal the Chaos Emerald and the fortress falls.
Trivia
- First part of the Chaos Emerald story, which continues in No Hedgehog Is an Island and New Echidna in Town; in production order the three parts alternate with the Origins trilogy.
- The French title, La forteresse volante, translates the English title directly.
- In the US this aired 1 October 1999, and the next new episode was Wedding Bell Blues on the 4th.
Watch the Episode
The full episode, uploaded by WildBrain’s official Sonic The Hedgehog – WildBrain YouTube channel (checked 6 November 2026).
Part of our Sonic Underground episode guide. The series page covers the characters, the songs, the prophecy and the show’s history.
Sources: titles, writers, songs and air dates from Luke’s original Sonic Scene guide, cross-checked with Wikipedia, Sonic Wiki Zone and Sonic Retro (Wayback copy); synopsis written for Sonic Scene from the episode, its official description and several fan references; title card and screenshots via Sonic Wiki Zone, copied to our media library.