Zeos

Zeos was a planet at war with its neighbour Atrios. The planet was governed by the supercomputer, Mentalis, created by the Time Lord Drax. Mentalis was programmed to self-destruct if threatened; the explosion would destroy Zeos and Atrios. The Doctor and Drax managed to disable Mentalis just before its countdown sequence completed. The Doctor diverted an attack by the Marshal of Atrios away from the planet. (DW: The Armageddon Factor)