NATO

NATO (North Atlantic Treaty Organisation) was an Earth-based organisation. Harry Sullivan went to work for NATO after leaving the Doctor. (DW: Mawdryn Undead) The Brigadier contacted him on behalf of UNIT. (BFU: The Wasting)

A rogue NATO commander was killed by an Ogri in Little Caldwell. This stopped NATO from discovering that the commander was responsible for abducting both aliens and humans. (NA: Return of the Living Dad)

The clone of Martha Jones used the memories of her counterpart to access the NATO Defence System and cancel any attacks made against the Sontarans. (DW: The Poison Sky)