UNIT

UNIT was an international military organisation which operated under the auspices of the United Nations, originally under the name of the United Nations Intelligence Taskforce until being renamed the Unified Intelligence Taskforce, Its remit was to investigate and combat paranormal and extraterrestrial threats to the Earth, (TV: Spearhead from Space) to protect humanity, no matter what. UNIT was not the only alien defence organisation, but it was certainly the one with which the Doctor had the closest personal involvement.