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".

Trivia
It is actually humorous to consider how a Master Chief Petty Officer is that of a Naval rank whom does not in any manner enter combat for any reason, whilst the Master Chief is always in warfare.