Sergeant (The Five Doctors)

A sergeant was on Colonel Charles Crichton's UNIT staff at the time of the Brigadier's retirement. (TV: The Five Doctors)

behind the scenes
This sergeant was originally meant to be Benton, however John Levene declined because in the script he would have to not recognize the Second Doctor. Also, Levene thought that Benton would have remembered that version of the Doctor and not made such a mistake.