Doomsday weapon

The Z-Bomb was an example of a doomsday weapon developed on Earth by 1986; with two or three placed at strategic positions around the globe, they had the potential to split the planet in half. (TV: The Tenth Planet)

In an attempt to intimidate John in 2050, K9 Mark 2 claimed to possess a doomsday weapon. (TV: The Custodians)

On Uxarieus, the Uxarieans devloped the Doomsday Weapon. (TV: Colony in Space)

One of the weapons available to Cousin Justine thanks to Grandfather Paradox's shadow was a doomsday weapon. Shuncucker matched this with a "double doomsday weapon". Neither of the two were exactly sure how either of these weapons work, but were certain that their activation would mean certain death for both of them. Thus, they mutually agreed to drop the weapons without using them. (AUDIO: A Labyrinth of Histories)