Master chief petty officer

Master Chief Petty Officer is the ninth enlisted rank of the UNSC Navy and is a non-commissioned officer. It is equal in rank to Master Gunnery Sergeant and Sergeant Major in the UNSC Marine Corps.

In informal settings, Master Chief Petty Officers are typically called "Master Chief" or "Chief." It is due to this that many people misinterpret John 117's rank as Master Chief Petty Officer, and not his true rank which is Master Chief Petty Officer of the Navy.