Non-Commisioned Officers (NCO's) is a type of rank given to men without a commision. They are enlisted men who never attended College, or Officers school.
The units they command range from Squads, to Platoons.
They are mainly combat leaders, and to execute whatever mission they are given. They are also selected to be Drill Instructors to train men.
They usually pass on the orders Officers give them to the enlisted men.
The ranks for NCO's are Corporals, Sergeants, Staff Sergeants,Technical Sergeants(now Sergeant First Class), Master Sergeants, First Sergeants, Sergeant Majors, Command Sergeant Majors, and Sergeant Major of the Army.