From Halopedia, the Halo wiki
Lieutenant, Junior Grade, abbreviated to LTJG, is a junior commissioned officer rank of O-2 in the United Nations Space Command Naval Command (NAVCOM) rank structure; including the UNSC Navy and Office of Naval Intelligence. It is preceded by Ensign, and subordinate to a Lieutenant.[1]
Command of staff section.[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