Repulsor

A repulsor was the component beneath the base unit that made the Dalek casing capable of flight. (AUDIO: The Enemy of My Enemy) It was activated by the vocal command "Elevate". (TV: Dalek)

At the beginning of Dalek history, the Dalek War Machine casings were incapable of flight. During the early days of the Dalek Empire, the Daleks initially used hoverbouts to traverse uneven terrain before they invented the repulsors. (PROSE: The Astounding Untold History of the Greatest Enemies of the Universe)

Despite continuing to operate a rusted War Machine, the casing of the Dalek Prime Strategist possessed a repulsor. (WC: The Sentinel of the Fifth Galaxy, AUDIO: The Enemy of My Enemy)