NATO

NATO (North Atlantic Treaty Organisation) was an Earth-based organisation. Harry Sullivan worked for NATO after leaving the Doctor. (DW: Mawdryn Undead) The Brigadier contacted him for 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 attacks made against the Sontarans. (DW: The Poison Sky)