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].
You should be women, and yet your beards forbid me to interpret that you are so. -- Shakespeare, Macbeth I.iii