The Supremacy was a spaceship discovered by Ferran in the far future. It was built by a race who had long since been wiped from history by the time Ferran found it. It was four kilometres long and one kilometre in diameter, with one thousand floors. It was controlled by a sentient computer that was initially programmed to respond only to Ferran's voice-print. Ferran said that the Supremacy was made from Kladenium.
When the Eighth Doctor commandeered the space shuttle Atlantis to confront Ferran, although the computer calculated that Atlantis could never defeat the Supremacy as a head-on collision wouldn't even scratch it, the Doctor was able to temporarily disable the ship's defences by mimicking Ferran's voice over the radio and ordering it to shut down. The Doctor later used the same vocal mimicry to transfer control of the Supremacy to himself and Miranda. (PROSE: Father Time)