C19 pre-dated UNIT and started in the late 1950s. Following the Shoreditch Incident of 1963, it took over responsibility for the Intrusion Countermeasures Group (ICMG) which handled that event. Group Captain Ian Gilmore, formerly of the ICMG, headed C19.
In the early 1970s, Martyn Townsend ran the Vault, intending to use its equipment for his own end. Townsend secretly received orders from Tobias Vaughn, believed by most to be dead, giving Vaughn considerable influence over the C19 organisation. (PROSE: The Scales of Injustice)
Shortly before the arrival of the Third Doctor on Earth after he had been exiled by the Time Lords, C19 was compromised by both the Master and Townsend, both of their respective agents infiltrating via the Glasshouse medical facility. They had differing agendas, but Townsend would assist in the Master's attempts to drive off investigative journalist James Stevens. These infiltrations led to C19 having an antagonistic relationship with UNIT, becoming a threatening agency towards civilians and anyone who had been involved in UNIT operations, and attempting to assassinate both civilians and the nominal C19 commanders. Both would be eventually revealed and driven out. (PROSE: The Scales of Injustice, Who Killed Kennedy)
From the early 1970s (PROSE: The Scales of Injustice) to as late as 1989, after C19 had been cleaned up, Sir John Sudbury ran the department. (PROSE: Business Unusual) Circa 1982, Sudbury asked the Fifth Doctor to investigate the disappearance of a Concorde aircraft. (TV: Time-Flight) Years later, he brought in the Doctor to investigate SenéNet. (PROSE: Business Unusual)
C19 was responsible for the Glasshouse, a medical facility for soldiers who had nervous breakdowns as a result of alien encounters.
While officially its mission was to liaise with UNIT and maintain certain facilities such as the Glasshouse, C19 also had "black" projects. (PROSE: Who Killed Kennedy) C19 was the part of the British government that funded UNIT UK. (PROSE: Dominion)
It maintained "the Vault" where it kept such things as de-activated Dalek shells and, after its de-activation, the sentient computer WOTAN. It used these to try and develop new military technologies and other, grotesque experiments such as infusing humans with Auton or Cyberman characteristics. (PROSE: The Scales of Injustice)
C19 was supposedly closed down in 1993, (PROSE: Instruments of Darkness) but they encountered the Eighth Doctor in Sweden, 1999 (PROSE: Dominion) and were still operating in 2002. (AUDIO: The Tao Connection)
Behind the scenes
- C19 and Sir John Sudbury are first mentioned in TV: Time-Flight, which is the first and only on-screen reference made to the organisation. The reference first gets completely explained in PROSE: Who Killed Kennedy, written by David Bishop.