From Halopedia, the Halo wiki
Gunnery Sergeant, abbreviated to GYSGT, is a Enlistment rank of E-7 in the United Nations Space Command Unified Ground Command (UNICOM) rank structure. It is preceded by Staff Sergeant and subordinate to a Master Sergeant and First Sergeant.[1]
Initial assignment.[1]
Enlisted: Crewman Recruit • Crewman Apprentice • Crewman • Petty Officer, Third Class • Petty Officer, Second Class • Petty Officer, First Class • Chief Petty Officer • Senior Chief Petty Officer • Master Chief Petty Officer
Enlisted: Private • Private, First Class • Lance Corporal • Corporal • Sergeant • Staff Sergeant • Gunnery Sergeant • Master Sergeant • First Sergeant • Master Gunnery Sergeant • Sergeant Major