Master chief petty officer
From Halopedia, the Halo wiki
File:Masuer Chief.jpg
The only known Master Chief Petty Officer, SPARTAN-117.
Master Chief Petty Officer is the ninth, and highest enlisted rank in the UNSC Navy, just above Senior Chief Petty Officer and below Ensign, and they are the equivaent to Master Gunnery Sergeant in the Marines, and is a Non-commissioned officer.
In informal settings, Master Chief Petty Officers are typically called "Master Chief" or "Chief".
