TARDIS

A TARDIS — sometimes styled Tardis, but also called a TT Capsule or just a timeship — was the primary space-time vehicle used by the Time Lords of Gallifrey.

Name
Susan claimed to have invented the acronym "TARDIS" from the phrase "Time And Relative Dimension In Space", (TV: An Unearthly Child) either on her first trip inside such a ship (AUDIO: The Beginning) or while she lived on 1963 Earth. (PROSE: Time and Relative) However, the First Doctor expressed familiarity with the term when Susan first said the word "TARDIS" aloud (AUDIO: The Beginning), and one source suggests that the term TARDIS already existed on Gallifrey prior to the Doctor's departure. (TV: The Name of the Doctor)

"TT capsule" was an early name for TARDISes, used during the Racnoss War. (AUDIO: Empire of the Racnoss) Many years later, some Time Lords like Castellan Spandrell preferred that more generic term, (TV: The Deadly Assassin) with Romana I using the shorter term "capsule". (TV: The Pirate Planet) Others, like the War Chief, (TV: The War Games) Commander Maxil, Damon, Lord President Borusa, (TV: Arc of Infinity) and Fabian, (TV: The Name of the Doctor) were perfectly familiar with the "TARDIS" acronym.

As Bill Potts pointed out to the Twelfth Doctor, though, the acronym would likely only work in English. (TV: The Pilot)

Some beings on the fringes of Time Lord society, like the Sisterhood of Karn, also knew the acronym without being prompted by the Doctor or his companions. (TV: The Brain of Morbius)

Susan defined the acronym with both the singular dimension (TV: "An Unearthly Child") and the plural dimensions. (AUDIO: The Beginning)

Vicki used the plural "dimensions" when explaining the term to Steven. (TV: "The Watcher")

This interpretation held for a time, being used by Zoe Heriot, (TV: The War Games) K9 Mark II, (TV: The Creature from the Pit) and Adric. (TV: Four to Doomsday)

Nevertheless, the singular Dimension, was preferred by the Doctor's fifth, (TV: Frontios) eighth, (TV: Doctor Who) ninth, (TV: Rose) tenth (TV: Smith and Jones) and twelfth incarnations, (TV: The Pilot) as well as the Doctor's TARDIS itself, when its matrix was transplanted into Idris, (TV: The Doctor's Wife) and Rose Tyler. (TV: Turn Left) The Seventh Doctor, however, used the plural "dimensions" to describe the TARDIS. (TV: Delta and the Bannermen)

The "dedication plaque" in the Doctor's TARDIS also referred to the ship as "Time and Relative Dimension in Space", favouring the singular form. (TV: Amy's Choice)

The Twelfth Doctor once claimed to Osgood that he made up the term TARDIS from the initials, "Totally and Radically Driving in Space". Osgood also mentioned that she had heard "a couple of different versions" of what TARDIS stood for. (TV: The Zygon Inversion)

During the War in Heaven, increased materialism on the Homeworld led to the word "timeship" being a more common name for the capsules. (PROSE: The Book of the War).

It was referred to as "The Ghost Monument" during its time on the planet Desolation when it appeared once every few thousand rotations. (TV: The Ghost Monument)

Flight
TARDISes usually moved through time and space by "disappearing there and reappearing here," (TV: Rose) a process known as "materialisation". This was controlled by a component called the dematerialisation circuit. (TV: Terror of the Autons)

If a TARDIS' relativity differentiator was missing or malfunctioning, then a TARDIS could only reappear in a different location in time, and not space. (COMIC: The Stolen TARDIS)

TARDISes also could fly through space like conventional spacecraft, but doing so for prolonged periods could damage the ship, at least in the case of the Doctor's TARDIS. (TV: The Runaway Bride)

A TARDIS was meant to have six pilots; (TV: Journey's End) however, the Doctor piloted the TARDIS on his own which led to it often jumping about in the Time Vortex and being an unpleasant ride for the passengers.

During operation, a distinctive grinding and whirring sound, nicknamed the vwoorpy by Alice Obiefune, (COMIC: The Then and the Now) was usually heard. (TV: An Unearthly Child et al.)

River Song once demonstrated that the Doctor's TARDIS was capable of materialising silently, teasing the Doctor that the noise was actually caused by him leaving the brakes on. (TV: The Time of Angels)

However, other newer TARDISes, flown by other pilots such as the Master, (TV: Colony in Space, The King's Demons) the Rani (TV: Time and the Rani) and the Monk, (TV: The Daleks' Master Plan) made the same sound in the course of their normal operation, as did the Doctor's when piloted by other Time Lords. (TV: The Claws of Axos, The Pirate Planet)

The Minyans' computer recognised the sound as associated with Time Lord ships. (TV: Underworld)

The Doctor himself also materialised his TARDIS more than once without making the distinctive noise. (TV: The Dalek Invasion of Earth, The Impossible Astronaut, The Time of the Doctor) The Eleventh Doctor explained that this was possible by putting the engines on silent. (TV: The Impossible Astronaut)

This sound was also made by other devices: SIDRATs, a craft similar to TARDISes used by the War Lords; (TV: The War Games) a Time Lord who appeared to the Third Doctor (without using any visible means of transport) to warn him of the appearance of the Master; (TV: Terror of the Autons) when the Time Lords provided the Third Doctor with a new dematerialisation circuit, it appeared on a table making this sound; (TV: The Three Doctors) and when the Doctor modified Skagra's invisible spaceship to travel like a TARDIS, again, this sound was heard. (TV: Shada, AUDIO: Shada)

When a TARDIS materialised, it would sometimes result in a strong wind and small tremors, enough to shake wine glasses, in the area where it appeared. (TV: Love & Monsters, Smith and Jones, The Eleventh Hour, The Lodger, The Big Bang, TV: End of Days) The Fifth Doctor once explained that this was caused by "Ionisation. Particles in the air being shunted around; making space." (AUDIO: The Boy That Time Forgot)

If a TARDIS materialised in a space occupied by another object, that object would usually appear inside the TARDIS. (TV: Bad Wolf, The Snowmen, The Return of Doctor Mysterio) However, once, the Eleventh Doctor landed an incomplete TARDIS in his own TARDIS and on top of an Ood, causing the Ood to be atomised. (TV: The Doctor's Wife)

Conversely, a TARDIS could dematerialise while leaving its occupants behind. (TV: Blink)

If a TARDIS landed in the same space and time as another TARDIS (TV: The Time Monster), or even if they simply collided while in the vortex, a time ram could occur, destroying both TARDISes, their occupants and even cause a black hole that would tear a hole in the universe — one the exact size of Belgium. (TV: Time Crash). However, time rams could be avoided by materialising inside the other TARDIS. This act itself also had inherent dangers, including space loops. (TV: Logopolis, Space / Time).

TARDISes had trouble materialising during time loops. (TV: The Lodger, TV: The Wedding of Sarah Jane Smith, TV: The Pirate Planet), and severe time distortions would make it impossible for a TARDIS to land without a signal to lock onto. (TV: The Angels Take Manhattan)

Types
TARDISes were generally referred to using the nomenclature Type X (TV: The Pirate Planet et al.) or X-form. (PROSE: The Book of the War et al.) The earliest known model of TARDIS was the Type 1, which was poorly designed, dangerous to operate, and difficult to start. Some of them had minds of their own, with a history of escaping and roaming the Universe. (PROSE: Heart of TARDIS)

There were at least 160 different numbered variants of TARDISes. (AUDIO: Intervention Earth)

Professor Chronotis had a Type 12 TARDIS. (PROSE: Shada)

The First Doctor had a Type 50 TARDIS (AUDIO: Prisoners of Fate) before he escaped Gallifrey in an out-dated (TV: The Doctor's Wife) Type 40 (PROSE: The Deadly Assassin, The Ribos Operation, et al.) Mark 3. (TV: Let's Kill Hitler) The Monk's TARDIS was a "Mark 4", and the First Doctor noted that there had been "quite a few changes" made compared to his own model. (TV: "Checkmate") By the time of the Doctor's fourth life, the entire Type 40 line had been retired from use. (TV: The Deadly Assassin)

The Master had a Type 45. (PROSE: The Dark Path) Anzor's TARDIS was a Type 60 (AUDIO: Mission to Magnus) The fifth incarnation of the Doctor once remarked that he should have upgraded to a Type 57 TARDIS. (TV: Warriors of the Deep) On another occasion, he noted that a Type 70 would allow him to break through a temporal distortion grid, but that his Type 40 was not cut out for such a "brute force approach". (AUDIO: Singularity) Romana II, (AUDIO: A Blind Eye) the Clocksmith, (AUDIO: The Doomsday Chronometer) and Vansell used Type 70s. (AUDIO: The Sirens of Time)

The Type 90 was the first generation engineered for war. Their pilots were regenerated to meld into the machinery; they primarily blocked off time travel routes that could be used for enemy escape during combat. (PROSE: The Book of the War) Christine Summerfield described them as big brass spheres. (PROSE: Dead Romance)

War TARDISes could map their interior dimensions onto the outer dimensions, appearing deliberately indiscreet. (PROSE: The Ancestor Cell, The Book of the War) Both Type 91s (PROSE: The Brakespeare Voyage) and Type 94s were War TARDISes. (PROSE: The Quantum Archangel)

On more than one occasion, the Doctor encountered heavily armed battle TARDISes carrying time torpedoes, developed during their fifth incarnation or earlier. (COMIC: The Stockbridge Horror, AUDIO: Neverland)

After the Eighth Doctor attached Compassion V's Remote receiver to his TARDIS, (PROSE: The Blue Angel) the Block Transfer Calculations changed her biodata and she became the first and only Type 102 TARDIS. (PROSE: The Shadows of Avalon, The Book of the War) Before this, another TARDIS was stated to be a Type 102, used by Epsilon Delta. (PROSE: The Dimension Riders) Later, model numbers would become standardised so that ‘Type 102’ referred only to Compassion. (PROSE: The Book of the War)

The Time Lords knew that, during the War in their future, they would be using humanoid TARDISes. (PROSE: The Shadows of Avalon, Alien Bodies) Lady President Romana III sent Celestial Intervention Agency operatives in Type 98 TARDISes to capture Compassion, but she escaped. (PROSE: The Shadows of Avalon) The Second Doctor was briefly assigned a Type 97 while working for Celestial Intervention Agency. (PROSE: World Game)

While Compassion still evaded them, the Great Houses began the 101-form Project to engineer humanoid timeships without Compassion's help. They tried to upgrade an old TARDIS, but she went mad and escaped; (PROSE: Toy Story, The Book of the War, Of the City of the Saved...) they also tried to pull one of Compassion's future children, Antipathy, backwards through time into their control. However, neither project succeeded. (PROSE: Of the City of the Saved...)

Eventually, Compassion made a deal with the War King and agreed to mother the humanoid "103-form" (PROSE: The Book of the War) or "Type 103" TARDISes. The Eighth Doctor met a Type 103 named Marie during the auction for the Relic. (PROSE: Alien Bodies)

Dimensionally transcendental


One of the key features of a TARDIS was that the interior existed in a dimension different from the exterior. The main application of this concept was that they were bigger on the inside than the outside. (TV: An Unearthly Child et al.)

This feature required use of "dimensional dams", which, upon the death of a TARDIS, would leak through. One such effect of this was the TARDIS exterior growing to a gargantuan size. According to the Eleventh Doctor, this was called a size leak. (TV: The Name of the Doctor)

The Fourth Doctor once tried to explain the phenomenon to Leela by using two boxes, one smaller than the other. He placed the larger one further away, so it appeared as if it could fit within the small box. He then explained that if the big box could be accessed where it was from the small box, the small box would be "bigger on the inside". However, Leela dismissed this as "silly". (TV: The Robots of Death) Nardole later used a similar analogy to Bill Potts, stating she’d have to imagine “a very big box fitting inside a very small box”, before adding “[she’d] have to make one”, and that it’s the second part people have trouble with. (TV: The Pilot)

Chameleon circuit
One feature of TARDISes was their ability to blend into their surroundings once they landed. If working properly, a chameleon circuit could assess the surroundings of a time and place just before arrival and change the exterior to resemble something common to that landscape. (TV: An Unearthly Child, Rose, Boom Town)

On the one occasion that the Doctor temporarily got the chameleon circuit on his own TARDIS working again after leaving London in 1963, it selected forms very incongruous to its surroundings. (TV: Attack of the Cybermen)

However, were the mechanism functioning correctly, it would have also been programmable from a keyboard on the TARDIS' main console. The Doctor once demonstrated to Adric how he would change the TARDIS into a pyramid, if the chameleon circuit were functioning properly.(TV: Logopolis)

The Master was able to produce an architectural column in sometimes incongruous environments like the Pharos Project or Heathrow Airport (TV: Logopolis, Castrovalva, Time-Flight), and the Monk stated that he chose to make his TARDIS look like a Saxon sarcophagus. (TV: "Checkmate") The Doctor once entered the Monk's TARDIS and changed its appearance from a pillar of stone to a police box identical to his own TARDIS. (TV: The Daleks' Master Plan)

When on Gallifrey, and presumably not utilising the chameleon circuit, some TARDISes were seen to resemble a plain rectangular cabinet with an outwards-sliding door on the front — a form also used by SIDRATs. (TV: The War Games)

When the Doctor stole his Type 40 TARDIS from the repair shop, it and others nearby resembled stone cylindrical structures with sideways-sliding doors. (TV: The Name of the Doctor) The TARDIS that the Twelfth Doctor and Clara Oswald stole from the same workshop had the same exterior design as the others. This TARDIS also had a broken chameleon circuit, as stated by Ashildr leaving it stuck in the form of an American diner after landing on Earth in Nevada. (TV: Hell Bent)

Organic machines
TARDISes were incredibly complex machines. The nature of their construction was such that they were said to be grown rather than constructed. (TV: The Impossible Planet) This could be done either from a seed (PROSE: The Nameless City) or a cutting (AUDIO: Black and White).

Because computers were unable to withstand the reality-changing stress, TARDISes required morphologically unstable living organic matter, or protoplasm, for their Block Transfer Computations. The outer plasmic hull, interior configuration, and a host of other details were derived from this function, as well as possibly a TARDIS' link with the Eye of Harmony. (PROSE: Cat's Cradle: Witch Mark)

According to the Second Doctor, his TARDIS was a microbiologically sterile environment. (TV: The Moonbase)

Sentient machines
Due to the level of complexity in their construction, TARDISes had a degree of sentience, and they could even take independent action, as when the Doctor's TARDIS resurrected Grace Holloway and Chang Lee. (TV: Doctor Who) Some advanced TARDISes, such as Compassion, were fully sentient beings in their own right. (PROSE: The Shadows of Avalon) Two near TARDISes could engage in a psychic conversation, audible by the bystanders. (COMIC: The World Shapers)

TARDISes often "mourned" the death of their Time Lord pilots, even committing suicide by flying into a sun or hurling themselves into the Time Vortex. The Fifth Doctor claimed there was "an elephants' graveyard" of TARDISes somewhere at the end of time. (AUDIO: Omega, The Axis of Insanity)

Since they were considered alive, a graveyard for TARDISes was provided in an under croft beneath the Capitol on Gallifrey. (PROSE: Engines of War)

In a parallel world, the death of the Tenth Doctor caused the TARDIS to slowly die. (TV: Turn Left)

In another alternative timeline, the Eleventh Doctor's death had the same effect on the TARDIS, though on this occasion the ship's dimension dams started breaking down, causing the exterior to grow. The console was also replaced by an "open wound" into the Doctor's time stream. (TV: The Name of the Doctor)

Even if in their first travels the First Doctor showed to be not fully aware of the conscience of his machine, (TV: "The Brink of Disaster") since the Doctor's TARDIS displayed these organic traits, he considered it to be alive. He talked to and stroked parts of the TARDIS when he operated it. (TV: School Reunion)

He spoke of mechanical difficulties as medical or biological conditions like "indigestion" (TV: Doctor Who, The Impossible Planet) and "digesting". (TV: The Runaway Bride)

He once commented that a TARDIS was "more like a person". (TV: The Five Doctors)

On one occasion, the Doctor's TARDIS manifested an avatar to help him fight a mental battle, taking on the forms and personas of the various companions who had ridden in it – however, this was when the Doctor was unconscious and battling within his own mind. (COMIC: The Forgotten)

When Amy told him she thought him mad for talking to a time machine, the Eleventh Doctor told her the TARDIS could, in fact, hear him. (PROSE: Night of the Humans)

When Chang Lee seemed to activate the Doctor's console upon leaning on a pillar and had the wooden doors to the Cloister Room open in front of him automatically, explained that the TARDIS liked him. (TV: Doctor Who)

When the matrix of the Doctor's TARDIS was placed inside the body of Idris, it was shown that they were, in fact, sentient beings who did possess some degree of free will. The TARDIS said, in its human body, "All of my sisters are dead." She also told him that the navigation problems that had plagued him throughout his travels were due to her taking him where he "needed to go" rather than just where he wanted to go. (TV: The Doctor's Wife)

The Eleventh Doctor told Alice Obiefune that a bond existed between a TARDIS and the individual who piloted it. If the bond was broken and the TARDIS could no longer "trust" the individual flying it, a TARDIS was programmed to return to Gallifrey. If unable to return to Gallifrey, a TARDIS was then programmed to find the next nearest Time Lord.

After the Doctor's TARDIS locked him out and left him in 2015 London, the Doctor believed his bond with the TARDIS was broken. He later found the TARDIS and was shocked when his mother stepped out in full Gallifreyan robes. (COMIC: The Comfort of the Good)

Security features
Before a TARDIS was fully functional, it needed to be primed with the symbiotic nuclei of a Time Lord's cells to create a molecular stabilisation system to protect a TARDIS' occupants against destabilisation. Once it was properly primed, it could be used safely by any species. (TV: The Two Doctors)

If a TARDIS were to be used by anyone other than its owner and his familiars, it would assault their minds, which may lead to memory loss. (PROSE: Echoes of Future Past)

When the TARDIS needed more power to take off, a series of circuits known as Architectural Configuration enabled rooms to be jettisoned to provide this power. This feature was used to escape both a gravity bubble and Event One (TV: Logopolis, Castrovalva), and to provide the extra power required to both leave the universe and re-enter it. (TV: The Doctor's Wife)

When the TARDIS was under attack from physical objects, the pilot could activate siege mode. This turned the exterior into a cube etched with Gallifreyan writing and sealed the entrance. (TV: Flatline)

"Every TARDIS" was equipped with a spare "empty dimension", a conduit to which could be opened to imprison someone in with a button in the control room, as the Fourth Doctor did to the Malevilus Magog. (COMIC: Doctor Who and the Iron Legion)

A TARDIS had the ability to trap intruders by ensnaring them in a space loop and sealing its doors. The Doctor's TARDIS did this to Gregor Van Baalen, Tricky Van Baalen, and the Eleventh Doctor after the former stole an orb from its Architectural reconfiguration system. (TV: Journey to the Centre of the TARDIS) The Twelfth Doctor told Journey Blue that she would "starve to death looking for the light-switch" if she shot him and attempted to commandeer the TARDIS. (TV: Into the Dalek)

Computer interfaces
TARDIS computer interfaces included:
 * An Index File provided text-based research into all manner of subjects relevant to TARDIS pilots and crew. This was accessible to Nyssa and Tegan. (TV: Castrovalva)
 * A voice interface could be requested for a variety of purposes. The TARDIS was able to communicate with its occupants using a holographic avatar, based on the Brigadier, and also created re-enactments of events from history, with characters based on the previous Doctors and their companions. (AUDIO: Zagreus) The Eleventh Doctor once got medical analysis and limited psychological counselling from this interface. (TV: Let's Kill Hitler)
 * A device compatible with 21st century Earth DVDs was capable of reading and executing automated piloting instructions for a TARDIS. (TV: Blink) It also could burn software to CD/DVD media for use on Earth computers. (TV: World War Three)
 * Psychic circuits kept a TARDIS linked to its crew when they left its interior, providing translation from alien languages and perhaps other features, so long as its attending Time Lord was in good health. (TV: The End of the World, The Christmas Invasion, et al.)

The Doctor's TARDIS
The First Doctor stole his TARDIS. (TV: The War Games)

At the time he had "borrowed" it, it was on Gallifrey for repairs. (TV: Logopolis, The Name of the Doctor)

However, the TARDIS itself, temporarily in the human body of Idris, said that it had planned for him to steal it; it had left its doors unlocked so that he could walk in. It considered itself to have "stolen" the Doctor as much as the Doctor thought they had stolen their TARDIS. (TV: The Doctor's Wife)

By the time of their fourth incarnation, all Type 40s had been decommissioned, save his. (TV: The Deadly Assassin) Following the events of the Last Great Time War, the was the last TARDIS in existence. (TV: Rise of the Cybermen, The Doctor's Wife)

According to the Moment, the sound of the TARDIS materialising was enough to bring hope to anyone who heard it, no matter how lost they were. (TV: The Day of the Doctor)

Possessed by other renegades
The Master had at least two TARDISes. According to the Doctor, the Master's had a Mark II dematerialisation circuit. (TV: Terror of the Autons)

The Rani, (TV: The Mark of the Rani) the Monk (TV: The Time Meddler) and Iris Wildthyme (PROSE: The Scarlet Empress) also had TARDISes.

While not technically a "renegade," Salyavin (a.k.a. Professor Chronotis) possessed a Type 12 TARDIS, with its controls appearing as simple panels hidden in an old book cupboard-type cabinet, and its control room "desktop" set as a university professor's library and study; his main TARDIS' disguise was that of his quarters at Cambridge University. As an older Time Lord who was retired on Gallifrey, Chronotis was not allowed to possess a TARDIS. (PROSE: Shada)

Ashildr and Clara Oswald's TARDIS
Stolen by the Twelfth Doctor from the Workshops on Gallifrey, the Doctor and Clara Oswald described the interior of this TARDIS as "basic" and "all white". The control room resembled that of the Doctor's TARDIS during his early travels with it. It had a console, scanner screen, panels with Time Lord writing and inner doors. The Doctor used this TARDIS to visit the final moments of the universe, encountering Ashildr there.

This TARDIS was, after the Twelfth Doctor erased his memory of Clara Oswald, piloted by Clara and Ashildr. They used it to return to Earth to retrieve the Doctor's TARDIS and then moved it to Nevada. They were unable to get the chameleon circuit working, leaving it stuck in the form of an American Diner. After dropping the Doctor off, Clara declared that she would return to Gallifrey "the long way around", using the TARDIS to have some more adventures of their own. (TV: Hell Bent)

Unique TARDISes
Compassion (a former member of the Remote) evolved into a TARDIS, the prototype of the sentient Type 102, the only one of that type. The first generation of mass produced sentient TARDISes was the Type 103. (PROSE: The Shadows of Avalon)

Idris and the Eleventh Doctor also built a junk TARDIS out of dead TARDIS parts from the Bubble universe's junkyard. (TV: The Doctor's Wife)

Other types of TARDISes
A Type 98 TARDIS had a holographic scanner. (PROSE: The Shadows of Avalon)

Copies of TARDIS technology
During the Doctor's second incarnation, the renegade Time Lord known as the War Chief provided similar time ships called SIDRATs to the War Lords to further their plans of conquest. When they learned of this, the Time Lords placed a force field around the War Lord homeworld. (TV: The War Games)

The Fourth Doctor instructed Skagra's ship on how to alter her own circuitry so she could de- and re-materialise like a TARDIS. (TV: Shada)

When the Skith probed the Doctor's mind, they gained knowledge of the TARDIS and made their own version, the SKARDIS. (COMIC: The Age of Ice)

When the Daleks achieved time travel, they made a version of the TARDIS, the Dalek time machine. (TV: The Chase)

The Daleks built a fleet of TARDISes identical to the Doctor's TARDIS. (COMIC: Return of the Daleks)

When Banto Zame and Sally-Anne Stubbins were running their conning operation, they used a device called a "STARDIS" which was a teleport device housed inside a portaloo. (AUDIO: The One Doctor)

The Cult of Skaro utilised the Genesis Ark, a Time Lord prison ship reserved for Daleks that could carry millions at a time. (TV: Doomsday)

An alternate reality UNIT, under the command of Rose Tyler, used technology taken from the Doctor's dying TARDIS to create a time machine to send the alternate Donna Noble back in time to correct history. (TV: Turn Left)

79B Aickman Road was a copy of TARDIS technology. (TV: The Lodger) The Eleventh Doctor later encountered a ship of identical design belonging to the Silence. (TV: Day of the Moon)

Is it T ardis or TARDIS?
Is "TARDIS" somehow "more correct" than "Tardis"? It's an open question, really. Here's what can be safely said.

The acronym was introduced into written English as "Tardis". The earliest Doctor Who publications — like 1960s Doctor Who annuals — consistently styled it as the ordinary word "Tardis", capitalising the T and often italicising the word in deference to the fact that it was a ship name. As David J. Howe and friends once noted in a behind-the-scenes exploration of An Unearthly Child: "Tardis was originally intended to be the name of the Doctor's ship (in the same way that one might name a sailing boat) rather than purely a descriptive acronym."

- The Television Companion

This explains why World Distributors' Doctor Who annuals often styled the name Tardis, not TARDIS, TARDIS or even "the Tardis". Common sentences in early 1960s annuals ran along the lines of, "The Doctor made his way back to Tardis, where Ben and Polly were waiting for him."

World eventually stopped italicising Tardis, but they used "Tardis" throughout their stewardship of the Doctor Who annuals, with the form being used as late as their final edition in 1986.

Similarly, Radio Times listings have always treated the acronym like a regular word. Even in the 21st century, "Tardis" is the form found in dictionaries, such as the Oxford American Dictionary. Like laser and sonar, then, "Tardis" is what some linguists call an anachronym. Since most of the general public doesn't know that it is an acronym, its heritage as an acronym is viewed as anachronistic, and therefore forgotten.

Different styles for different times
That said, a few generalisations can be noted. Throughout most of the classic run — at least prior to John Nathan-Turner, the preferred form was Tardis. Thus, in Target novelisations, annuals, and other printed material that was actually contemporaneous with the original version of Doctor Who, Tardis is the form of choice.

This began to change somewhat in the 1980s. Once Doctor Who became a print-only franchise in the 1990s, however, "TARDIS" became standardised by Virgin Books. BBC Wales continued with the Virgin/BBC Books style. Publications like the Doctor Who Storybook, New Series Adventures, Quick Reads, The Darksmith Legacy and the like are all fairly unanimous in their use of "TARDIS".

Nevertheless, despite the increased use of "TARDIS" in prose fiction, there still is no firm preference expressed by narratives in visual media like television episodes and comic stories. Where the word has appeared, it has done so along other words exclusively set in the uppercase. For instance, in the plaque installed on the Eleventh Doctor's TARDIS set, all the words are in uppercase, so nothing can be inferred about the "proper" way to capitalise the acronym. Equally, in Let's Kill Hitler, the word appears on a screen where all other text is in uppercase. Comic depictions have also been lettered in all uppercase, as is standard for the medium.

In popular culture
In terms of general cultural references, "Tardis" is still in heavy use, as is evidenced by article titles like "XDm .45 ACP 3.8″ Compact is the Tardis of Handguns" and BBC America's Where's the Tardis? competition. It also seems to be BBC News' house style to go for the sentence case version: "'Tardis' to tackle anti-social behaviour in Brighton" and "Tardis Tennis", a game made by BBC Sport. Moreover, most articles supplied by BBC News about Doctor Who — as opposed to those written for the Doctor Who official website — tend to use "Tardis" throughout the body of the text, as with this coverage of the 2012 official Doctor Who convention. Equally, it has always been the house style of the Radio Times to use this form, as can be evidenced by exploring the RT website, as well as past RT clippings included on classic-era DVDs.

Use on this wiki
On this wiki, "TARDIS" refers to the time-travel device used by Time Lords, whereas "Tardis" means the wiki itself.