Slightly larger and similar in shape and colour to a bronze Dalek casing, the Ark was dimensionally transcendental and contained millions of bronze Daleks. The Ark also sported a set of hemispherical controls which the Daleks' suction cups could interact with, though they remained unable to open it themselves. Like the Daleks' themselves, the Genesis Ark was impervious to human bullets as well as the firepower of the Cybermen from Pete's World. (TV: Doomsday)
During the Last Great Time War, the Time Lords used the Genesis Ark to imprison millions of bronze Daleks. The Doctor, who fought in the war, remained unaware of this. As the Tenth Doctor later reflected, both sides had secrets.
The Cult of Skaro took the Genesis Ark and escaped the war in a Void Ship, intending to use it to re-establish the Dalek Empire after they returned to the universe in 2007. However, though the Daleks could bring the Ark to its final stage of awakening, it could only be opened by the touch of a time traveller which was a safeguard to stop the Daleks from liberating their fellows from the prison ship.
The Daleks would have blown up the Sun to force the Ark open, but first they attempted to coerce Rose Tyler to open it. During a firefight with the Cybermen, Mickey Smith accidentally laid his hand on the Ark, priming it. As the Ark required 30 square miles for activation, the Daleks escorted it out of Torchwood Tower and into the sky. High above Canary Wharf in London, the Ark opened and the Daleks within began pouring out.
When the Doctor reopened the breach to the Void, the Genesis Ark was sucked back through along with the Daleks and Cybermen, as they were all saturated with "Void stuff". (TV: Doomsday) Barring a portion of Cybermen, all those within the Void were eventually wiped out as a result of the reality bomb. (TV: The Next Doctor)