Staff sergeant (SSG) is E-6 rank in the U.S. Army, just above sergeant and below sergeant first class, and is a non-commissioned officer. Staff sergeants are generally placed in charge of squads, but can also act as platoon sergeants in the absence of a sergeant first class. In support units, staff sergeants ordinarily hold headquarters positions because of the number of slots available for them in these units. Staff sergeants are typically assigned as a squad leader or company operations non-commissioned officer in charge at the company level, but may also hold other positions depending on the type of unit. Staff sergeants are referred to as "Sergeant" except in certain training environments and schools. The NATO code is OR-6.