Type 55 was a model of TARDIS used by the Time Lords on the planet Gallifrey for travel through time and space. The Type 55 was more advanced than the Type 40. By the outbreak of the Last Great Time War, they were an older type of TARDIS, but during the war all models of TARDIS were being re-commissioned for use in the fighting.
When they were exiled from Gallifrey by Mantus, Narvin judged that the TARDIS he and Romana II were forced to leave in was a Type 50 or Type 55 TARDIS. Romana observed that theirs was a reconditioned model, and that Mantus would not have allowed for them to have one of the new ones. (AUDIO: Assassins)
Behind the scenes
- When illustrating the "Gallifreyan" TARDIS that Narvin had judged be a Type 50 or 55 for the cover of Time War: Volume Three, cover artist Tom Newsom opted to use the TARDIS design seen in the television story Hell Bent over the similar TARDIS design first seen in 2013's The Name of the Doctor.