What is the rank of Carter on the television show Hogan's Heroes?

On the TV show Hogan's Heroes, Sergeant Andrew Carter (lieutenant in the premiere episode) was the explosive specialist of 'Hogan's Heroes'. He was often looked down on from the others because of his many mistakes and dim-witted comments. Newkirk could be considered his best friend. He also was very talented at gin rummy. Carter was played by Larry Hovis.