UNIT's personnel have a wide range of weaponry to call on, some custom-made to combat specific threats.
In a series of interviews originally recorded for the 2006 DVD of the Doctor Who serial Inferno (1970), actor Nicholas Courtney, who played Brigadier Lethbridge-Stewart in The Invasion, similarly described The Invasion as a "dummy run" for the idea of the Doctor, the main protagonist of Doctor Who, being exiled to Earth.
Dicks also said that the idea of exiling the Doctor was done because making every serial take place on Earth was cheaper to produce than if every serial had to have a new alien planet built, and that UNIT was an idea Sherwin had come up with to answer the question of what to do with the Doctor after he was exiled to Earth.
Operating under the auspices of the United Nations, its purpose is to investigate and combat paranormal and extraterrestrial threats to the Earth.
In the original Doctor Who series, several UNIT personnel (such as the Brigadier) played a major role in the programme.
Speaking in an interview on the 2011 special edition DVD of Spearhead from Space, Sherwin claimed that he had created UNIT because he wanted to give some "considerable support" to the Doctor, "so that [Troughton] didn't have so many damn lines to learn each week".
Sherwin told Doctor Who Magazine in 2014 that while working as script editor on the Doctor Who serial The Web of Fear (1968), which also involved an army, he told scriptwriters Mervyn Haisman and Henry Lincoln to include all of the characters that he had originally invented for The Invasion.
They are also shown utilising heavy weaponry such as bazookas, machine guns, mortars, and in Terror of the Zygons (1975), a depth-charge launcher.), SIG P226 pistols, and for heavy duty, use Stinger missile launchers.
They wear PLCE pouches on police tac-vests, and also wear riot-protection arm pads and gloves, and have side-handle batons and quick-cuffs for arrests.
In a 2014 interview with Doctor Who Magazine, script editor Terrance Dicks recalled that he was present at the "birth" of UNIT during the production of the Doctor Who serial The Invasion (1968).