Incubation level

The incubation level was the lowest level of the Dalek City, where new Dalek mutants were grown before being placed in their casings. As a result of its value to the Dalek race, the level appeared on no floor plans and was designed to automatically isolate in the event of the Master Room being compromised. It was also for this reason that the ruling Dalek Supreme resided on the level, so that it could lead the revived Daleks to victory. (AUDIO: Return to Skaro)

When the Thal-Dalek battle knocked out the City's primary power source, (TV: The Daleks) the incubation level was sealed off and, without any Daleks to operate the systems, placed in a state of hibernation. After decades in such a state, the Supreme and the embryos were awakened by the Thal scientist Tryana stumbling upon the incubation level. Manipulating Tryana, the Supreme began placing the matured embryos in casings while extending the tunnel to reach the Thal City. When the First Doctor later returned to Skaro, he and Susan Foreman separately deduced the incubation level's existence, and entered it from Level 13. The Supreme accelerated its stratagem in response, activating the hundreds of Daleks it had grown and leading its troops out from the level to attack the Thal City, later retreating back to their own city through it. (AUDIO: Return to Skaro)