Intrusion Counter-Measures Group
Intrusion Countermeasures Group was an arm of the British military which acted as a predecessor to UNIT, intended to take action against covert threats to British soil. They were formed in 1961 under the command of Group Captain Ian Gilmore, who drafted scientific specialists like scientist Rachel Jansen under the Peacetime Emergency Powers Act.
The group encountered the Daleks and the the Doctor in 1963, in what became known as the Shoreditch Incident. They were shut down soon after. (DW: Remembrance of the Daleks, MA: Who Killed Kennedy)
The Intrusion Countermeasures Group was composed of Royal Air Force personnel and equipment.