Alan Mace

Colonel Mace was a British officer with UNIT. He wanted to lead an attack against the Sontarans but the Doctor convinced him otherwise after the deaths of a squad of soldiers including Ross Jenkins. He tried to launch a nuclear attack against the Sontarans, but the Martha clone wiped out the launch codes.

Mace co-ordinated the UNIT counter offensive at the ATMOS factory. Instead of using normal weapons which could be stopped by expanding the copper bullet, he used bullets without a coating so he could attack the Sontarans. He also orders the Valiant to be used to clear the ATMOS gas. He killed Sontaran Commander Skorr with a pistol. (DW: The Sontaran Stratagem/ The Poison Sky)

Behind the Scenes
In the exclusive clip for Turn Left, which is set in an alternate timeline slightly before the events of Series 3. Mace is heard talking to Private Harris since Harris is heard talking to Trap One, Mace's codename.