Gunnery Sergeant (UNSC)
From Halopedia, the Halo wiki
Gunnery sergeants are commonly referred to by the informal abbreviation "gunny." This nickname is usually regarded as a title of esteem and/or cameraderie, and is generally acceptable for use in all situations except formal and ceremonial ones. Use of the term by lower-ranking personnel, however, remains at the gunnery sergeant's discretion.
