A Terror Squad was the Eighth Legion's doctrine distilled into a single formation, warriors trained not merely to kill but to make of their killing a weapon aimed at every survivor's mind. They infiltrated ahead of an assault to butcher sentries and commanders in the dark, arranging the aftermath with grim artistry so that those who found it would break before the true attack ever began.
Everything about them was calculated for dread, the silence of their approach, the horror of their work, the certainty that no wall or watch could keep them out. A single Terror Squad could unmake the morale of an entire garrison, spreading a contagion of fear that did the Legion's work more cheaply than any bombardment. In the Heresy they turned these arts upon loyalist and civilian alike, the sharp edge of a Legion that had made a science of atrocity.