UNIT dating controversy The UNIT dating controversy is a problem of retroactive continuity ( retcon ) which has attracted considerable interest from fans and professional " Doctor Who " writers alike . It has also been the subject of a 2 | entertain DVD documentary , " The UNIT Dating Conundrum " , included in the special edition release of " Day of the Daleks " . It has even made its way " back " into DWU narratives . These have most prominently included a sly remark made by the Tenth Doctor in " The Sontaran Stratagem " and on - screen graphics seen in " The Lost Boy " — but writers in other media have occasionally referenced the controversy , or attempted to solve parts of it . " The Enfolded Time " solves the UNIT dating controversy stating that due to the Doctor ' s numerous visits to the 1970s and 1980s in his faulty TARDIS , the two decades merged into one making 20 years of history happen in 10 and the obvious mix around of some of this history . The essential problem . Though replete with additional nuance , the nub of the narrative problem is easy to grasp . " Mawdryn Undead " tells viewers that the Brigadier retire d from UNIT in 1976 . However , the events of " The Invasion " , the first story in which UNIT properly appears , approximately occurred in 1979 . Thus , the UNIT dating controversy is , broadly speaking , an attempt to understand how the Brigadier could have retire d from UNIT before UNIT even existed . Writer Ben Aaronovitch has notably opined that there is simply no way to retcon the problem . Terrance Dicks has said he deliberately avoided giving dates during his time as script editor precisely so he could avoid these sorts of continuity headaches . Consequently , the biggest period of UNIT involvement , the Third Doctor ' s era , has only comparatively mild contributions to the dating controversy . Digging deeper . No television story actually featuring UNIT gives a clear year . " Day of the Daleks " comes close . It implies at one point that Jo Grant had just said the year , but Terrance Dicks was keen to keep the dating deliberately vague . The problem , which arguably should be called " the Brigadier dating controversy " , exists primarily because of two appearances of Alistair Gordon Lethbridge - Stewart when he wasn ' t employed by UNIT . The first was his debut story , " The Web of Fear " , when he was still a colonel in the regular British Army . Here , he meets the Second Doctor , Jamie , Victoria and crucially , Professor Edward Travers . Victoria says that they met Travers in 1935 in the Himalayas , which they did in " The Abominable Snowmen " . It is further revealed that 1935 was " over forty years ago " , tacitly setting " The Web of Fear " approximately in 1975 if not after . In a later adventure , called " The Invasion " , the Second Doctor again encounters the newly - promoted " Brigadier " Lethbridge - Stewart . The Brigadier says their last meeting was " four years ago now " , ostensibly putting " The Invasion " approximately in 1979 . Viewers got no dialogue with a firm year for the whole of the Third Doctor ' s era . In " Pyramids of Mars " , however , it is claimed several times that Sarah Jane Smith is from " 1980 " , and they briefly revisit the year . Since she was the Third Doctor ' s final companion , and spent a good deal of time at UNIT , this has some implication for the theoretical date of UNIT stories set in seasons 11 - 13 . It ' s not particularly clear what to make of the statement . One possibility given by " The UNIT Dating Conundrum " is that the entire lot of UNIT stories from " Spearhead from Space " to " The Seeds of Doom " ( where the Brigadier is still in UNIT but away in Geneva ) happens from 1979 to 1980 ; if Sarah is speaking of her " home time " , i . e . the time she ( and Harry Sullivan ) left with the Doctor , that would imply " Planet of the Spiders " , " Robot " , and possibly " Terror of the Zygons " when Harry leaves the TARDIS , would take place in 1980 . Whatever the case , her statement is not a clear violation of the continuity established by " The Web of Fear " . It does , however , indicate that the following " contemporary " stories of " The Android Invasion " and " The Hand of Fear " would have to take place in or after 1980 as Sarah encounters Harry and leaves in the two stories , respectively . " The Seeds of Doom " does not necessarily have to fit here . What breaks UNIT dating is " Mawdryn Undead " . This story firmly and explicitly has the Brig retiring from UNIT in 1976 , the year " The Seeds of Doom " came out . The Fifth Doctor confirms that " a year later " from the retirement is 1977 , which offers viewers no wiggle room whatsoever . Because it ' s flatly impossible to have the Brigadier retiring " before " he ' s even " become " the Brigadier , a fundamental discrepancy indisputably exists in televised " Doctor Who " narratives . Other dating problems . Other problems with the timeline exist . Contradictory clues . There are many other details that confuse the picture . Off - screen evidence . Published books , contemporary interviews , publicity material and behind the scenes documents all point to uncertainty amongst the production team as well . Other media . Stories in other media have also offered dates for the UNIT stories but have had little success in producing a clear answer :