Greyhound Four
From Tardis Wiki, the free Doctor Who reference
Greyhound Four was a UNIT call sign which was once used by Jo Grant. (TV: The Green Death) It was also used by John Benton. (HOMEVID: Wartime) When caught in the 1970s, Kate Stewart used Greyhound Four to contact Trap One, her father the Brigadier. (AUDIO: The Sacrifice of Jo Grant)
