Ionising tower

The ionising towers were a network of Skaronium-alloy towers that existed in the wilderness of Skaro fifty cycles following the Thal-Dalek battle, designed to reduce the level of background radiation in the planet's atmosphere. Fuelled by a static electricity dynamo, the towers fired bursts of electricity that were guided by nano-particles to other towers.

History
When the Daleks were defeated in the Thal-Dalek battle, the incubation level of the Dalek City isolated itself. Two years prior to the First Doctor's return to Skaro, the Thal scientist discovered the level and met the Dalek Supreme. Duping the Thal into thinking it wanted peace, the Supreme provided Tryana with the blueprints for the tower network, which it intended to one day claim as a weapon against the Thals. Unwilling to trust her fellow Thals with the knowledge that the Daleks had survived their defeat, Tryana claimed credit for inventing the towers.

When the First Doctor returned to Skaro, he and his companions reacquainted themselves with the Thals at the main tower. Following the Doctor, Tryana and Ian Chesterton discovering the Daleks' hostile intentions, the former two were captured while the latter fled into an underground tunnel, witnessing two Dalek drones take control of the main tower. At the Dalek Supreme's order, they reprogrammed the tower to discharge directly into the Thal City, though they ceased to do so when the Dalek army arrived.

Using a discarded Dalek casing, the Doctor and his companions managed to retake the tower network, the Doctor reprogramming it to target the Daleks themselves. Retreating as a result of this, the Dalek Supreme made plans to disable the tower network before the Dalek City was overloaded and destroyed. (AUDIO: Return to Skaro)