The Arch Tardis was a concept ship proposed by Captain Bandar's own renegade war Tardis. The Tardis's defiance in eradicating a galaxy lead to it using the onboard weapon to instead take the galaxy into its interior dimensions. When Leela, Veklin and Rasmus were sent to investigate the reappearance of a world that should have been erased during the initial mission, their Tardis was overwhelmed through its telepathic circuits and drawn to the planet.
The Tardis would reveal itself to the group, its Matrix having hidden inside of Bandar's next incarnation. There, the Tardis made its proposal to end the time war. Rather than fight the Daleks, it hoped to persuade Rassilon to allow it to extend its interior dimensions through merging with every other Tardis and then use the weapon still contained within it to move the entire universe, galaxy by galaxy into itself, saving everyone, not just the Timelords and leaving the Daleks to inhabit the empty remains of N-space.
Having already drawn in another Tardis, it attacked the dimensional dams. When this proved ineffective, it decided to use its control over its interior to edit the timeline to shape events to a more favourable outcome. Veklin voiced that its plan was unfeasible, as the expansion of the universe would mean that more and more Tardis's would have to be grown and added to itself to compensate. To counter, it used the telepathic circuits in an attempt to make the group attempt the merging anyway. When Rasmus remained unconvinced, it attempted to use Leela, feeding her the information required to complete its plan. After she was shot by Rasmus, the Arch Tardis was abandoned. The chronal energy it had built up detonated the ship, the entire galaxy it contained, and a nearby Dalek fleet.