Time Ram – Explosive destruction of two or more TARDISes which occurs if they attempt to occupy exactly the same location in space-time. Time ram was a danger whenever one timeship attempted to materialize inside another [OS: Logopolis]. Jo Grant initiated a time ram against The Master‘s TARDIS to prevent him escaping from Atlantis, but they were saved by Kronos [OS: The Time Monster]. The Doctor would later attempt to use a time ram against Magnus Greel [MA: The Shadow of Weng-Chiang], The Nine [BF: Relative Time], Bianca [BF: The Wormery], and the Timewyrm [NA: Timewyrm: Genesys]. Varnax attempted to destroy the Doctor by ramming the TARDIS with his ship, the Jonah. The Doctor exploited Varnax’s three-dimensional thinking to cause him to ram himself instead [US: The Mark of Varnax]. Varnax was able to avoid complete destruction by performing a temporal inversion. The Doctor later performed a time ram on the Master’s TARDIS to close a Warp Shunt. Both TARDISes were destroyed, though the Doctor retained a Seed Crystal from his TARDIS when he escaped by using the Master’s recall device to teleport himself to the Morthrai colony ship [US: The Final Problem]. The Master escaped by using the Sword of Rassilon, though it was lost in the process [TDA: Death in Heaven].
Driving away from the wreck of the day and it's finally quiet in my head. Driving alone, finally on my way home to the comfort of my bed. And if this is giving up, then I'm giving up. -- Anna Nalick, Wreck of the Day