The HADS (Hostile Action Displacement System) was one of the defence mechanisms of a TARDIS. Upon the outer shell of the vessel coming under attack, the unit dematerialised the TARDIS and rematerialised it a short distance away, in a safer locale. (DW: The Krotons)
- The Doctor's TARDIS frequently came under attack without the HADS activating, which suggests that either the system was not always switched on, or that only attacks assessed as having a certain threat level triggered a response.
The HADS of the TARDIS belonging to Drax could apparently be manually triggered when the vessel was coming under fire, but the account detailing this is probably apocryphal. (Search for the Doctor)
