Republican Security Forces

The Republican Security Forces (RSF) were a parallel version of UNIT on Earth in a parallel universe.

History
The RSF was founded in 1959 by Major James Lethbridge-Stewart and Captain Marianne Kyle. (PROSE: The Schizoid Earth) Shortly after its establishment they battled the Bannermen in Wales, from whom they obtained artificial gravity and fast drive technology which allowed them to construct a base in space. (PROSE: The Face of the Enemy)

During the 1960s, the RSF fought many alien threats under the leadership of James Lethbridge-Stewart, including the Great Intelligence and the Axons. (PROSE: Night of the Intelligence) They would also carry out general security operations, investigated political criminals, and did expeditionary work abroad. Internal security work as done by the Security Directorate, based out of Leconfield House in Mayfair, which was part of External Security despite the existence of Internal Affairs and their Auxpol organisation — ExSec and Internal had a famously bloody rivalry. (PROSE: I, Alastair)

The RSF's encounter with the Great Intelligence brought them into contact with the Master's counterpart Koschei, who helped them battle the Intelligence at the expense of his TARDIS, which was ruined though the console was salvaged. The RSF tortured Koschei and Ailla, eventually killing her though it's unknown if she somehow survived through regeneration.

When the RSF reviewed recordings of the Doctor's TARDIS arriving in their universe, they realised they could do the same with Koschei's own TARDIS. They tortured him, forcing him to go through his regenerations rapidly until he had none left and was kept alive, in agony, on life-support systems. (PROSE: Night of the Intelligence)

However, the RSF could not avoid being drawn under the control of James's power hungry father, Gordon Lethbridge-Stewart. By the end of the 1960s, Gordon had taken the reigns of power and alienated James through his ultranationalist policies. James fled to another Earth using technology stolen from the Axons. (PROSE: Night of the Intelligence)

The RSF sent an Expeditionary Force to Aden in the late sixties, where Column Leader Alastair Lethbridge-Stewart was involved in "punishment raids" to crush the rebelling locals.(PROSE: I, Alastair)

Lethbridge-Stewart later transferred to the Security Directorate and, to his annoyance, found it used by Party figures against each other, reporting their rivals and children of rivals for "crimes". The RSF made use of South African mercenaries at this time and the Directorate was run by Division Leader Spencer Pemberton. (PROSE: I, Alastair)

In the 1970s, they were stationed at the Eastchester scientific labour camp to guard the Inferno Project. Despite the arrival of the Third Doctor, they proved unable to stop the Primords or the Inferno Project from destroying the planet. (TV: Inferno)

However, Earth was not destroyed but was devastated beyond recovery — prompting the surviving leaders to start crossing over to the Doctor's world, planning to kill and replace their counterparts. (PROSE: The Face of the Enemy)

Behind the scenes

 * The ranks of the RSF are based, to an extent, on those of the real-world British Union of Fascists, such as Section Leader (lieutenant) and Company Leader (captain)
 * The RSF's weapons included the, (TV: Inferno) (PROSE: The Face of the Enemy) , , and the . (PROSE: The Schizoid Earth) Officers could privately purchase their own pistols instead of using standard equipment provided they were chambered for  or , Elizabeth Shaw used a , Alastair Lethbridge-Stewart used a , (TV: Inferno) and Marianne Kyle opted for a  machine pistol. (PROSE: The Face of the Enemy)
 * Leconfield House was the home of MI5 from 1945 to 1976.