Lieutenant commander

Lieutenant Commander is a commissioned officer rank of the UNSC Navy, equal to the rank of Major in the UNSC Marine Corps, UNSC Air Force, and the UNSC Army.

So far, Lieutenant Commander is the highest rank held by a Spartan-II in the case of Kurt-051 and Fhajad-084. Catherine-B320, a Spartan-III, also held the rank of Lieutenant Commander in Noble Team during the Battle of Reach.

In informal settings, Lieutenant Commanders are simply referred to as "Commander".