Exterminator (weapon)

The Exterminator was a giant weapon created by the Daleks. They intended to use it to destroy Earth. To defeat their plans, the Second Doctor derailed the train carrying the Daleks who had been trained to operate the Exterminator, then stole the weapon's instructions so he could learn to operate it himself. After destroying the two Daleks guarding the Exterminator, the Doctor used it to wipe out the rest of the Daleks and shoot down the Dalek Flying Saucers. Strangely, the Doctor made no move to destroy the weapon itself afterwards. (TVC: The Exterminator)