Ensign
From Halopedia, the Halo wiki
Ensign is a junior rank of commissioned officers in the UNSC Navy. It is equal in ranking with a Second Lieutenant in the Marines and is below Lieutenant (Jr Grade). In all probability Ensigns wear a collar insignia of a single gold bar sence the navy ranks are of thoe in the US navy and all insignia discribed in the books and seen in the games are the same as those in the US navy.
