Black hole converter

A black hole converter was a device which the Master placed on each of his warships. They were intended to destroy other planets once the Time Lord Empire launched its war against the Universe. When he lost control of Earth, he told the Tenth Doctor he would rather destroy it, but the Doctor talked him out of it. When time was reversed, the warships and black hole converter faded away. (DW: Last of the Time Lords)

During the Master's reign, the Drast stole a black hole converter from him and used it to create the Relativistic Segue in an attempt to leave Earth. (NSA: The Story of Martha)