An Automated Personnel Unit
Automated Personnel Units were a type of android constructed by both the Pralor and Cravic around the early 23rd century. Programmed to fight in a war being waged between the two groups, both types of units were of a very similar design: humanoid in form with "faces" having only the most basic of features. The primary external difference was that the Pralor units had a silver colored metallic covering while Cravic units had gold colored ones. Pralor units included designations 3947 and 6263 while Cravic units included a designation 122. Both Pralor and Cravic units were also designed with chromodynamic power modules – power sources intended to be non-reproducible as a safeguard against the androids becoming self-reproductive. Automated Unit 3947 displayed the ability to discharge chromodynamic energy through his hand as an offensive weapon powerful enough to at least knock two people unconscious.
Eventually the Pralor-Cravic war came to an end and both sides agreed to deactivate their Automated Personnel Units. The units on both sides, sensing a threat to their existence, turned on both the Pralor and Cravic, exterminating both races, and resumed the war.
In 2372, the USS Voyager discovered a non-functioning Pralor unit. B'Elanna Torres reactivated the unit, and was able to determine a means to reproduce the chromodynamic power module such that other androids could be powered. When she realized that allowing the Pralor units to procreate would vastly alter the balance of power in the conflict (and possibly the quadrant), she destroyed her work and allowed the remaining automated personnel units to continue their war. (VOY: "Prototype")