Titan Base was a large filling station on Titan. As of the year 5000, it had a crew of four. Three of them worked in shifts, arriving on the base by Titan shuttle and staying until a relief crew arrived. The fourth crew member was the commander, who seemed to have been a permanent inhabitant of the base.
That same year, a relief crew infected by the Swarm took over Titan Base and tried to turn it into a Hive. The Fourth Doctor ignited fuel tanks at the base, which coupled with methane in the atmosphere to create an explosion that destroyed the base. (TV: The Invisible Enemy)
During his seventh incarnation, the Doctor returned to Titan Base in the company of Ace and Hector Thomas in 4920. The TARDIS had been commandeered by Hector, who had fallen under the control of the Swarm. The Swarm ensured its own creation by returning to the Bi-Al Foundation on K4067, where it mutated from the Saturnian plague. (AUDIO: Revenge of the Swarm)