The Hostile Action Displacement System, or HADS, was one of the defence mechanisms of the Doctor's TARDIS. When the outer shell of the vessel came under attack, the unit dematerialised the TARDIS and rematerialised it a short distance away after the attacker had gone, in a safer locale. (TV: The Krotons) However, another function of this was a "dispersal" instead of a "displacement", which would allow for the TARDIS to appear to actually be blown apart, but in fact remaining intact in various pieces. (TV: The Witch's Familiar)