The Imperial Dalek mothership was the mothership of the Imperial Dalek faction commanded by Davros. It was known in the Daleks' own language as Eret-mensaiki Ska, which translated as "Destiny of Stars".
According to the Seventh Doctor, the mothership potentially held as many as 400 Daleks, and possessed weapons that could easily crack open an Earth-like planet "like an egg". The mothership also contained a creche where Dalek embryos listened to indoctrination tapes while being fed nutrients. It was powered by a fusion reactor. One Dalek was plugged into the computer where it could control the creche and servo-robots on the outer hull of the ship. (PROSE: Remembrance of the Daleks)
On the planet Spiridon, Davros amassed an army of loyal Daleks, opposing the Emperor Dalek based on Skaro. After surviving an attack by the Emperor's forces, Davros took the mothership to Skaro. Once there, he seized control of the planet, destroying the Emperor Dalek and naming himself the new Emperor. (COMIC: Emperor of the Daleks!)
During the resulting Imperial-Renegade Dalek Civil War, Davros searched for the Hand of Omega, taking the mothership over Earth in 1963. Ultimately, the mothership was destroyed by the Hand of Omega. Davros was the only survivor, immediately fleeing from the ship when the Doctor refused to stop his attack. (TV: Remembrance of the Daleks)
There were a number of escape pods on board the vessel. Davros used one to escape when the Hand of Omega was used to destroy the mothership. (PROSE: War of the Daleks; AUDIO: Terror Firma, Daleks Among Us)