Who is Corporal, later Acting Sergeant, and Sergeant Schaldenbrand from The Killing Zone: My Life in the Vietnam War and what is their importance?

Schaldenbrand is a draftee from Philadelphia, Pa., described as a typical guy from a big city. Schaldenbrand has the habit of playing checkers with anyone available during any lull in the fighting and also brushes his teeth a lot. He does not like the war and does not want to be there, nevertheless, has considerable ability to lead. Sergeant Schaldenbrand helps Lt. Downs a lot and manages to survive his one year tour of duty in Vietnam without serious wounds. When Sgt. Schaldenbrand leaves, this creates a crisis for Lt. Downs. In the one instance where Lt. Downs is ordered to split the platoon on a combat operation, Sgt. Schaldenbrand leads the other half of the platoon but somehow goes in the wrong direction and walks toward Lt. Downs' half. Lt. Downs accidentally ambushes his own men. Luckily, only one man is wounded in the foot.