Type 45 was a type of TARDIS used by Time Lords. Compared to the Type 40, the Type 45 was more advanced. The Master once owned a Type 45 TARDIS. It had user-definable macros for navigation, something which separated it from the Type 40. (PROSE: The Dark Path) Maris heard rumours that some Type 45s could take on human form. (PROSE: Celestial Intervention — A Gallifreyan Noir)