Three of Five, a Borg tactical drone, being studied by the Hansens
A tactical drone was a type of drone utilized by the Borg Collective.
During their expedition to locate and study the Borg in the early 2350s, the Hansens managed to beam a tactical drone onto the USS Raven for examination. They determined its species was Ktarian, known to the Borg as Species 6961. Tactical drones possessed a tritanium infrastructure. (VOY: "Dark Frontier")
Hazari also made excellent tactical drones due to their violent nature and advanced technical abilities. (VOY: "Think Tank")
Two Borg Tactical Drones (2401)
In 2401, while gaining the schematics and location of a transmitter within a Borg cube, Captains Worf and William T. Riker were attacked by a pair of Borg tactical drones each possessing energy weapons on their wrists. Worf attempted to disable them using a kur'leth in close-quarters combat but was quickly injured and retreated behind a console with Riker. They were able to kill the Drones and continued on the mission using a concealed phaser in the hilt of Worf's kur'leth. (PIC: "The Last Generation")