Model 51

The Model 51 was a type of TARDIS. 
Gallifreyan cyberneticists' original intent when developing the Model 51s was to give them conventional sentience via artificial intelligence to such a degree that Time Lord pilots would become redundant, and TARDISes could fly themselves, at least on simple observational missions. This idea was gradually abandoned in favour of programming the Model 51s' Cybernetic Personality Matrix as a helpful "co-pilot" personality who could be a friend and equal partner to the pilot. 
However, even this hope proved ill-founded. Due to some basic design flaw which the engineers never pinpointed, the Model 51s' artificial personalities were unstable, constantly shifting from emphasising one personality trait to another — cycling through "balanced", "helpful", "stubborn", "protective", "sullen", "cautious", "complaining", "bossy", "hostile", "practical joker", "slow", "haughty", and "argumentative" spells at the slightest disturbance. Many were scrapped; most pilots of the survivors found them irritating to deal with and tended to dump them for good at Gallifreyan repair centers. Since such workshops were the prime venue for Celestial Intervention Agency to discreetly get ahold of new TARDIS units, this resulted in many Model 51s ending up in CIA hands, as exemplified by Rollo's TARDIS. (GAME: )
The engineers would only return to the ideal of sentient, self-operating timeships with the 101-form project, whose prototype once again proved to have an unstable, disobeident personality; (PROSE: The Book of the War) the Time Lords would only fully achieve their dream with the Type 103s. (PROSE: Alien Bodies, The Book of the War) 
Category:TARDIS variants
Category:Vehicles
Category:Time travel devices
Category:Gallifreyan technology
Category:Time technology