Void drive

In an alternate timeline where the Cybermen used Time Lord resources to conquer all of history, void drives were engines used by the Cybermen of the 24th century to transform the planets they conquered into spaceships. The Tenth Doctor believed that, following their conquest of Sontar, the Cybermen would install void drives into the Sontaran homeworld, which, in conjunction with their modifications to the Sontaran cloning factories, would allow them to pilot the planet across the universe as a breeding world to spread armies of millions of Cybermen across the universe. Ultimately, the Cybermen's conquest of Sontar failed after the Twelfth Doctor and Rassilon, on Gallifrey at the end of the universe, used the regenerative energy stored inside the Eye of Harmony to erase the Cybermen's conquests across time and space from history. (COMIC: Supremacy of the Cybermen)

In the original timeline, the Mondasians installed a similar type of engine into the core of Mondas to mobilise the planet and return to the Sol system. (AUDIO: Spare Parts) In the 22nd century, the Daleks attempted to mobilise Earth with similar engines on at least two occasions. (TV: The Dalek Invasion of Earth, AUDIO: Lucie Miller / To the Death)