Apocalypse Deathwatch was name of a space-time cruiser, which transported its passengers through time and space to spectate the destruction of worlds.
On one occasion, the passengers witnessed the fractures timeline of Earth being pulled through the Time Vortex. The explosion of the first TARDIS in history had caused a slow time explosion in the Vortex, trapping the cruiser and its passengers. The Fifth Doctor and Jenny worked together to stabilise the cruiser long enough to cauterise time, detach the bridge from the cruiser and return it to normal space. When the passengers escaped the Vortex, all memories of these events were erased. (AUDIO: Relative Time)