While The Doctor has rarely gotten along with military organisations due to his preferred pacifist, scientific approach to dealing with his enemies, the United Nations Intelligence Taskforce – later renamed the Unified Intelligence Taskforce – has generally been an exception to this rule, with the organisation retaining close ties to The Doctor from the moment of its creation and The Doctor generally turning to UNIT when circumstances require him to ask for help.
Established by the then- Colonel Lethbridge-Stewart after he aided the Second Doctor in defeating The Great Intelligence’s conquest of London (“The Web of Fear“), UNIT began as essentially a secret intelligence force, investigating evidence of potential alien activity on Earth and working to eliminate it before it could pose a serious threat to Earth. The British government had initially been resistant to this idea – most likely because they had already established Torchwood, a British organisation established by Queen Victoria in 1879 to hunt aliens on Earth, for such a purpose, even if Torchwood was outside their official control -, but Lethbridge-Stewart was still able to get the organisation established by appealing directly to the UN security council (“Who Killed Kennedy?”) (Although later sources have suggested that incidents such as the Seventh Doctor’s confrontation with the Daleks in Shoreditch in 1963 for the Hand of Omega inspired some elements of UNIT’s later operations (“Remembrance of the Daleks“), this group may have been affiliated with Torchwood rather than UNIT).
Although their first major challenge against the Cybermen invasion of Earth aided by Tobias Vaughn nearly met with failure when the British government was infiltrated by Vaughn’s brainwashed minions, The Doctor – visiting Earth once again after the TARDIS was slightly damaged – was again able to assist UNIT in protecting Earth, he and his companions aiding in UNIT’s campaign against the Cybermen by programming the computers to precisely calculate the missile trajectory needed to destroy the Cyber-fleet (“The Invasion“). Its existence is generally known to the public as a security organisation with scientific expertise (“The Three Doctors“), but it is typically assumed to be a more conventional counter-terrorist unit and intelligence recovery service rather than the alien-hunting agency it is in reality.
When the Third Doctor found himself exiled to Earth by the Time Lords, newly-regenerated and with his knowledge of how to operate or repair the TARDIS removed as punishment for interference in the affairs of the universe, he was soon willing to accept the offer to become UNIT-UK’s scientific advisor, offering them his knowledge and experience of alien technology in exchange for the resources needed to repair the TARDIS (“Spearhead From Space“). Although The Doctor had some trouble adjusting to life in the military, and still considered the repair of the TARDIS to be his first priority, he regularly proved himself to be a valuable asset, sometimes declining courses of action that could have resulted in his freedom in favour of helping his friends (“The Claws of Axos“), his co-workers at UNIT becoming a closest thing to a family that he had known since he originally left Gallifrey so many years ago. Aside from helping UNIT deal with immediate alien threats, he also provided them with minor examples of advanced technology, such as upgrading a satellite tracking station so that it could detect alien ships that other systems at this time would have missed (“The Devil Goblins From Neptune“), although he obviously declined to provide them with weapons. He also assisted in shutting down Department C19, a rogue division of UNIT responsible for recovering alien technology that sought to use it to aid its leader’s plans for world conquest before he was defeated while trying to trigger a war with the Silurians (“The Scales of Injustice“).
Although UNIT faced some political problems during this time, such as the British government somewhat resenting their lack of official control over UNIT (“The Claws of Axos”) or Control, the mysterious head of the CIA, regarding them as arrogant upstarts whose ties to The Doctor ‘proved’ that they couldn’t be trusted and trying to undermine their initial authority – only to prove himself incapable of handling any threat he couldn’t overpower with sheer military force – (“The Devil Goblins from Neptune”), UNIT’s track record with The Doctor assisting them was very successful. Working together, The Doctor and UNIT averted a wide variety of threats to Earth, such as The Doctor’s old friend-turned foe, The Master (“Terror of the Autons“), the powerful Axos (“The Claws of Axos“), the megolomaniacal BOSS supercomputer (“The Green Death“), and other assorted alien incursions. While The Doctor was primarily affiliated with UNIT-UK, his role as scientific advisor extended to allow other branches of UNIT to call on his services, such as Captain Valentine Shushkin of UNIT’s Russian branch requesting The Doctor’s help in investigating mysterious disappearances in a Suberian forest (“The Devil Goblins from Neptune”).
As well as the obvious threat of potential alien activity, UNIT were also dispatched to provide security for various international peace conferences (“The Mind of Evil” and “Day of the Daleks“), although their remit could sometimes be countermanded by the local governments when dealing with powerful individuals even if The Brigadier was still able to go over government heads to contact Geneva directly for assistance. Even after the TARDIS was restored to full working order (“The Three Doctors“), the Third Doctor continued to spend time at UNIT when he returned to Earth between travels until he regenerated once again (“Planet of the Spiders“). His new incarnation being a more Bohemian, independent personality than the gentleman scientist of his predecessor, the Fourth Doctor returning to his more casual wanderings through time and space (“Robot“) without maintaining a ‘home’ at UNIT, contacting UNIT only when he was specifically requested (“Terror of the Zygons“) or when circumstances demanded their assistance in the later stages of his adventures (“The Seeds of Doom“). However, UNIT maintained a particular interest in The Doctor; having established a secret vault for dangerous alien artefacts known as the Black Archive, UNIT also used it to assess The Doctor’s new companions whenever they were witnessed in the present while separated from The Doctor, taking the companions to the Archive to question them while relying on the Archive’s automatic defences to erase the companions’ memories of the visit in the aftermath (“The Day of The Doctor“).
Continuing the ‘tradition’ established by the Fourth Doctor, subsequent Doctors have only maintained intermittent contact with UNIT as a whole, preferring to handle situations using their own skills unless the situation requires larger -scale resources or they need to provide official credentials to confirm that they have the right to interfere, such as when the Fifth Doctor convinced the staff of Heathrow Airport to let him investigate disappearing airplanes (“Time-Flight“). Despite this, The Doctor has remained officially ‘employed’ as UNIT’s scientific advisor for at least the next few decades, providing The Brigadier with a space-time telegraph that his old friend can use to call for The Doctor if UNIT find themselves facing a situation where his presence would be beneficial (“The King of Terror” and “The Shadow in the Glass“). Although he became comparatively obscure in the 1980s after a period of time without contact with UNIT – to the point that Brigadier Winifred Bambera, commander of UNIT-UK in 1997, didn’t recognise The Doctor until she was told about him by one of her staff (“Battlefield“) -, The Doctor developed a significant reputation among UNIT as a whole in the late 1990s, The Brigadier once noting that it is a common reaction for the average UNIT soldier to be stunned into silence – three seconds of silence was considered an impressively short time – upon learning that The Doctor is involved in a crisis (“The Shadow in the Glass”) and The Doctor often having to specifically ask soldiers not to salute him despite him possessing no official rank in the organisation (“Planet of the Dead“). Although few soldiers know the full details about The Doctor’s interest in Earth, they are generally always aware that The Doctor can be trusted to help, with UNIT and The Doctor only coming into direct conflict under explicitly exceptional circumstances, such as when The Doctor’s enemy the Meddling Monk (“The Time Meddler“) provided UNIT with VR training equipment that subtly brainwashed them to see The Doctor as a threat (“No Future“).
It has so far been unspecified whether UNIT and Torchwood ever engaged in ‘territorial disputes’ over Torchwood’s interest in The Doctor and UNIT’s employment of him, Queen Victoria having declared The Doctor an ‘enemy of the crown’ after meeting his tenth incarnation due to that body’s somewhat jocular attitude towards the dangers he faced appearing dangerous to the Queen (“Tooth and Claw“). The most likely way to reconcile this anomaly is that The Brigadier was able to pull some strings in the UN to force Torchwood to stay away from The Doctor while he was actively working with them, with Torchwood only able to ‘legally’ capture The Doctor in “Army of Ghosts/Doomsday” because he was acting independently.
Although The Doctor retains ties to UNIT in the early twenty-first century, his affiliation with the organisation was more limited, The Doctor generally helping The Brigadier directly rather than UNIT as a whole, such as when The Brigadier – returned to UNIT in an advisory capacity as head of a small investigation department – contacted the Fifth Doctor for expert insight that wouldn’t stretch his department’s budget while investigating a company’s recent purchase of large quantities of plutonium (“The King of Terror”), or when he requested the Sixth Doctor’s insight into a strange videotape of a crashed spaceship (“The Shadow in the Glass”). While still willing to use his UNIT contacts if he must, by his ninth incarnation The Doctor preferred to avoid UNIT (“Aliens of London/World War Three“) as the Time Lord and the organisation began to differ in their preferred strategies, UNIT’s current officers typically displaying a greater willingness to resort to violence and more generally brutal measures as the first option against alien threats than the UNIT of the past. Although they retained some degree of their old morality, as seen with their condemnation of the Cortez Project – a branch that regarded all alien presences on Earth as an automatic threat to human life due to the risk of cultural contamination – (“Bullet Time“), with The Brigadier maintaining some authority in the organisation as a man The Doctor knows he can trust, at least some branches of the organisation assumed a more brutal attitude in areas such as the treatment of prisoners. A particular example of this was shown when UNIT kept former operative Toshiko Sato in prison for months without trial after she was blackmailed into stealing plans for a sonic device to save her mother, in clear violation of her human rights, before she was recruited by The Doctor’s former companion Captain Jack Harkness to serve as technical support for Torchwood Three (“Fragments“). UNIT’s darker attitude has also been reflected in its greater propensity for falling victim to external corruption, such as Colonel Karrim forming an alliance with The Shansheeth to steal the TARDIS from the Eleventh Doctor (“Death of The Doctor“) or an alien race called the Bane infiltrating UNIT to recover the near-mythical Black Scroll to awaken an ancient evil (“Enemy of the Bane“). Sarah Jane Smith has also maintained her distance from UNIT after adopting the genetically-engineered Luke following his rescue from the ruthless Bane because she feared that UNIT might experiment on him if they knew the truth, even if she still clearly trusts The Brigadier and her other UNIT colleagues, as well as retain enough ties for UNIT to assist her in being released from prison when she was framed on child abduction charges (Fake evidence suggested that Luke had actually been a real person rather than a creation of the Bane) (“The Lost Boy“).
Despite the tension between them in the present, many UNIT officials retain an admiration for The Doctor in particular even if they are sometimes tempted to disregard his advice and resort to the ‘easier’ option, such as Colonel Mace allowing former companion and current medical officer Martha Jones to call The Doctor for assistance (“The Sontaran Stratagem/The Poison Sky“) and UNIT scientific advisor Doctor Malcolm Taylor disobeying his superior’s orders to close a potentially dangerous wormhole simply to give The Doctor time to come back to Earth (“Planet of the Dead“).
The Doctor and Sarah Jane have also been shown to retain a certain appreciation for the organisation’s mission even if they disagree with its current methods, the two of them even nominating some friends and acquaintances – such as the Tenth Doctor’s companion Martha Jones (“Reset” and “The Sontaran Stratagem/The Poison Sky”), the presently-unemployed Nathan and Barclay (“Planet of the Dead“) and cleaner Adriana (“The Man Who Never Was“) – as new potential recruits for UNIT in the hope that they could help remind the organisation of its original purpose after they all impressed The Doctor and Sarah with their skills and compassion for others in a crisis. During an encounter with UNIT in the mid-2010s, the Eleventh Doctor was particularly pleased to learn that UNIT was now under the command of Kate Stewart, the daughter of The Brigadier, Kate leading UNIT with a focus on more scientific methods due to her having been inspired by her father’s stories of his friendship with The Doctor to follow the example set by her father’s friend (“The Power of Three“). Although their second meeting was more hostile when The Doctor learned that Kate was prepared to detonate a nuclear bomb that would annihilate London to stop a Zygon invasion after the Zygons infiltrated the Black Archive, with the aid of the Tenth Doctor and the War Doctor (The Doctor who fought in the Time War between the Time Lords and the Daleks), the Eleventh Doctor not only saved London, but ensured that humans and Zygons would draw up a mutually beneficial peace treaty by using the Archive’s defences to erase the memories of those present so that the disguised Zygons and their human templates would be unable to remember who they really were (“The Day of The Doctor”). During Kate’s third encounter with The Doctor, she was forced to deal with the triple issues of a Cybermen assault, the return of The Master, and The Doctor having regenerated into the Twelfth Doctor (“Dark Water/Death in Heaven“). Although Kate activated a long-standing UNIT protocol where The Doctor would be elected President of Earth in order to coordinate its defences, UNIT were powerless against The Master’s new army of the dead, but The Doctor was able to arrange for the army to destroy itself when Danny Pink – the boyfriend of current companion Clara Oswald – retained enough of his humanity to take control of the Cyber-army and command it to destroy itself. Although Kate fell out of a plane during the fight, she was caught by a Cyberman that turned out to be the converted Brigadier, reanimated by the Cyber-technology and holding on to his own humanity to save his daughter and kill The Master, allowing Kate to continue her family’s career protecting Earth with UNIT, proud to proclaim that Earth had The Doctor on the payrole.
Although UNIT will survive into at least the thirtieth century under the name Unitatus, with its purpose as a secret unit undermined as aliens become public knowledge, the organisation will lose a significant amount of credibility and influence over that time. Although they retained some power in the mid-twenty-second century – to the point that the organisation called The Doctor for help when investigating an arms deal for a supposedly ultimate weapon, although they accidentally contacted the Second Doctor in the early days of his life rather than a Doctor who knew of UNIT’s existence – (“The Murder Game“), UNIT’s status apparently went downhill after that. According to reports, they became a male-only political force by the twenty-fifth century, but suffered a serious setback when Commander Medford’s attempt to defeat the Time Lord ‘invasion’ of the Earth Empire – really an assault by a race called the Ferutu, revealed during the crisis to be the Time Lords from an alternate universe where Gallifrey was destroyed – resulted in Unitatus’s entire fleet being destroyed by the Ferutu and our timeline nearly erased as Medford attempted to destroy Gallifrey, before the Fifth Doctor and the Seventh Doctor managed to stop the Ferutu and erase their timeline (“Cold Fusion“). The Seventh Doctor’s companion Roslyn Forrester – an Adjudicator from the thirtieth century – briefly mentioned that the Unitatus of her time now spend their time organising charity events and debating whether Lethbridge-Stewart was hyphenated, the organisation’s original purpose now irrelevant and the task force itself near-useless despite their successful history in the twentieth and twenty-first century (“Cold Fusion”).