Colonel

Colonel is the highest field grade commissioned officer rank of the UNSC Marine Corps, UNSC Army, and UNSC Air Force, equal in rank to a Captain in the UNSC Navy. The rank insignia appears to be the same as the modern U.S. counterpart; one silver eagle.

Given that other ranks command the same unit groups as their modern day U.S. counterparts do, it is highly probable that a UNSC Colonel commands an Air Force wing, Marine regiment or an Army brigade. This has yet to be observed in the Halo universe. A Colonel may also serve as a staff officer for higher unit groupings, such as divisions.