Lieutenant Commander

From Halopedia, the Halo Wiki

Lieutenant Commander Affiliation UNSC Navy Higher Rank Commander Lower Rank Lieutenant Command Small Warships, Installations Known Lieutenant Commanders Xaing Cho J. G. Ortega Gail Purdy Miranda Keyes SPARTAN-051 "Kurt" (AKA Kurt Ambrose) SPARTAN-084 "Fhajad" Julian Waters Jilan al-Cygni
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Lieutenant Commander is a junior commissioned officer rank of the UNSC Navy, equal to the rank of Major in the UNSC Marine Corps 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.

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

UNSC Defense Force commissioned officer ranks
	O-1	O-2	O-3	O-4	O-5	O-6	O-7	O-8	O-9	O-10	Special (Wartime Only)
Air Force:	2nd Lt	1st Lt	Capt	Maj	Lt Col	Col	Brig Gen	Maj Gen	Lt Gen	Gen	GOAF
Army:	2LT	1LT	CPT	MAJ	LTC	COL	BG	MG	LTG	GEN	GA
Marine Corps:	2ndLt	1stLt	Capt	Maj	LtCol	Col	BGen	MajGen	LtGen	Gen
Navy:	ENS	LTJG	LT	LCDR	CDR	CAPT	RDML	RADM	VADM	ADM	FADM