From Halopedia, the Halo wiki
Sergeant, abbreviated to SGT, is a Enlistment rank of E-5 in the United Nations Space Command Unified Ground Command (UNICOM) rank structure. It is preceded by Corporal and subordinate to a Staff Sergeant.[1]
Squad leader.[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