De-mat Gun
The De-mat Gun was a powerful weapon of the Time Lords of the planet Gallifrey. A remark by Borusa implies that Rassilon had at least a hand in its construction or design. It could remove the target from space-time. The gun could not be armed without the Great Key of Rassilon.
As Lord President, the Doctor used the De-mat gun against the Sontaran leader Stor and his remaining troops in the Capitol on Gallifrey. The gun apparently vaporised itself, leaving only the Great Key. The Doctor could not then remember the last few days. (DW: The Invasion of Time
It was lost at sometime into The War, necessitating the Time Lords to research further more destructive weapons. (EDA: Alien Bodies, The Ancestor Cell)
It was recovered at one point before The Last Great Time War by the Eighth Doctor and Chantir. (IDW: The Forgotten)
