Staff sergeant
From Halopedia, the Halo wiki
Template:Rank Infobox Staff Sergeant is the sixth enlisted rank of the UNSC Marine Corps, and is a non-commissioned officer. It is equal to the rank of Petty Officer First Class in the UNSC Navy.
They typically command teams of 9 - 11 Marines, although they may be selected to become "Platoon Sergeant's", which aid Second Lieutenant's.
