Dimensional displacement system

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The dimensional displacement system protected the Doctor's TARDIS against Vortisaur attacks in the Time Vortex. Nonetheless, in one instance, the Vortisaurs were nearly able to break through the defences, and caused the system to fall to 22% effective. The extra momentum the Vortisaurs generated to push looping time ship wreck away, according to the Eighth Doctor, "should have caused enough of a power surge to restore the displacement system". (AUDIO: Storm Warning)