HADS

The HADS (Hostile Alien Displacement System) is the primary defence mechanism of a TARDIS. Upon detecting imminent danger to the physical structure of the Ship, the unit briefly dematerialises the TARDIS, and rematerialises it a short distance away, in a safer locale.(DW: The Krotons) The Doctor's TARDIS would appear to have a HADS with an intermittent fault, as it has, on occasions, remained in dangerous locations from which the HADS ought to have removed it.