"Voc" was a class of robot used by humanity on the planet Kaldor in the 29th century. (PROSE: Corpse Marker) They were green and gold in colour, and possessed the power of speech, unlike the lower Dum class. All Voc class robots answered to a Super-Voc, who acted as the co-ordinator of the command circuit.
Vocs were used as sandminer robots during ore gathering expeditions. Taren Capel secreted himself aboard Storm Mine 4, adopting the identity of Dask. While V16 was massaging Borg's arm aboard the sandminer, Chub told him that there was a Voc therapist in Kaldor City, specially programmed, equipped with vibro-digits, subcutaneous stimulators, the lot." While treating its first client for a stiff elbow, it had felt around the joint and then twisted the arm off at the shoulder. "Dask" asked what its reason was, and Chub replied that it had gone haywire. Dask replied that "a Voc class robot [had] over a million multi-level constrainers in its circuitry." All these, he said, would have to malfunction before it could perform such an action.
Capel used a laserson probe to corrupt the programming of several Vocs, including V4, V5 and V6. These robots were used to murder the human crew, strangling them once they were isolated. Kerril, Chub, Cass, Borg and Zilda were all killed in this way. Once the Super-Voc SV7 was converted to Capel's cause, the Vocs were commanded by it. When the need for secrecy perished, Capel deactivated those Vocs that weren't under his control, such as V16.
Vocs were able to detach their appendages, as V6 did its hand while pursuing Lish Toos. It abandoned its attack on her when SV7 sent out a priority call, summoning V6 to section J. V5 went unharmed when Leela threw her knife at it. However, the Fourth Doctor was able to damage the sensors of V4 by thrusting a laserson probe through its head. Toos and Uvanov followed the Doctor's instructions to create anti-robot bombs, with which they destroyed V5. Using a device based on one used by Capel, the Doctor created a "final deactivator" which he intended to use against robots at close range. D84 used this to destroy V6, sacrificing itself to do so. (TV: The Robots of Death)