Simcox, call-sign Bull, is a U.S. Marine.
Through unknown circumstances, Simcox joined the United States Marine Corps, where he gained the call-sign Bull.
He was dispatched by Schofield to lead half of the team into the missile silo to search for the Delta teams, whom they had since lost contact with. Inside the silo, Bull's team found one of the Delta teams, all dead, and reported the find to Schofield via radio, including the distrubing fact that Farrell's head had been cut off. Suddenly Bull and his team were ambushed by unknown enemies, all of them perishing.