The Aristotle, named after the Earth scholar, was a command ship in the Combined Galactic Resistance which fought against the Daleks. It was originally a hospital ship, but was repurposed because according to its commander Morgan Blue, “Daleks don’t leave any wounded and we don't take any prisoners.”
The Aristotle held Rusty, the first allegedly moral Dalek, prisoner, and was the base for the operation that shrunk the Twelfth Doctor, Clara Oswald, Journey Blue, Ross and Gretchen Carlisle in order to give them access to the inside of Rusty's casing in order to repair it.
However, once Rusty was repaired, it returned to its former immoral state and began a rampage inside the Aristotle. It also sent a distress call to a nearby Dalek flying saucer, and a battle ensued aboard the ship between the Daleks and the resistance fighters. The battle only ended once the Doctor telepathically linked with Rusty, turned him moral, and Rusty ordered the Dalek saucer to retreat and killed the ones already onboard. (TV: Into the Dalek)