Type 50

Type 50 was a type of TARDIS used by Time Lords. It was much more advanced than the Type 40s. The First Doctor owned a Type 50 TARDIS before leaving Gallifrey in a stolen Type 40 TARDIS. (AUDIO: Prisoners of Fate) Maris heard rumours that some Type 50s could take on human form. This was proven to be correct when the Doctor's first TARDIS appeared to her in the form of a young child. (PROSE: Celestial Intervention — A Gallifreyan Noir)