Heavy Gun Drones are a further development of the basic Gun Drone. They are visibly larger with heavier construction then standard Drones and carry heavier weapons in the shape of twin-linked Burst Cannons. On some Heavy Gun Drones, one Burst Cannon has been replaced with a Marker Light so the Drones can range ahead of the main Tau force and pick out targets for destruction via long-range Seeker Missiles. In this role, they act as effective robotic artillery spotters. Heavy Gun Drones are relatively new additions to the forces of the Tau and most versions are still undergoing field trials.