The Lifeboat was a boat with giant-sized skis fixed to it so it could travel across snowfields. It was built on Trenzalore while the Eleventh Doctor was living in Christmas and was used to transport goods and services over long distances.
About 300 years into his stay on the planet, the Doctor and several humans travelled on the Lifeboat to the Outland to investigate the death of Tiberius Gluck. They discovered that five Autons had parachuted to the surface to kill the Doctor. He lured them onto the Lifeboat, then blew it up on the frozen lake Lake Lagda. This damaged the Autons and they sank with the Lifeboat to the bottom of the lake. (PROSE: Strangers in the Outland)