The E-7 rank in the Army is sergeant first class. This level ranks higher than staff sergeant, sergeant, corporal, private first class and private. The E-7 rank equates to chief petty officer in the Navy and Coast Guard, gunnery sergeant in the Marines and master sergeant in the Air Force.
A sergeant first class works as a senior non-commissioned officer and typically oversees part of a platoon during battle. The sergeant first class is often in charge of up to 40 soldiers for training, mentoring, tactical logistics and casualty evacuations. He acts as a tactical advisor to the platoon leader and may take over as platoon leader if a commissioned officer is not available.