Void drive

In an alternate timelinewhere 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 planet 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 engine, a propulsion system, into the core of Mondas in order to pilot the planet away from the destructive Cherrybowl Nebula. (AUDIO: Spare Parts) The CyberMondans that the Mondasians were converted into used the propulsion system to pilot Mondas to Earth; in their attempted invasion of Earth in 1986, Mondas was destroyed. (TV: The Tenth Planet)

The Daleks that invaded Earth in 2153 attempted to replace the Earth's core with a similar engine in 2164. They were defeated by the First Doctor. (TV: The Dalek Invasion of Earth)