Trap One was a commonly used call sign in UNIT.
Trap One was used by Colonel Mace during Operation Blue Sky, (TV: The Sontaran Stratagem/The Poison Sky) and following the Racnoss invasion of Earth in a parallel world. (TV: The Runaway Bride) It was later used by Colonel Vikram Shindi. (AUDIO: Hosts of the Wirrn)
Behind the scenes
- The Trap One call sign appears to have been created to complement the Greyhound signs. "Trap" is the name given to a stall in which greyhounds are enclosed before the start of a race.