Lt. Southern was in charge of the American crew that working alongside the Russian naval crew on the Natalia as part of the Anti-terrorism treaty. When CTU Los Angeles agents discovered that the Dawn Brigade terrorist leader Vladimir Bierko had targeted the submarine for its weapons, Jack Bauer contacted Lt. Southern and informed him of the threat. Southern ordered his subordinate, Skeet, to set condition delta and to seal the bridge and aft hatches, and warned the ranking Russian officer of the danger. As Southern went topside with a pistol to investigate the exterior of the ship, he exposed the submarine to the threat by opening the hatch. He was shot in the head by Bierko, who then killed everyone else on the sub (except for Petty Officer Tim Rooney) with Sentoxnerve gas.