Second Lieutenant Affiliation UNSC Army UNSC Marine Corps UNSC Air Force Higher Rank First Lieutenant Lower Rank Warrant Officer Command Platoon (Army and Marines) Known Second Lieutenants Dalu McCasky Oros

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Second Lieutenant is a junior Company Grade Commissioned officer rank of the UNSC Marine Corps, UNSC Army, and UNSC Air Force; it is the lowest commissioned officer rank and is equal in rank to Ensign in the UNSC Navy. Second Lieutenants are given command of platoons, such as the case of Second Lieutenant Oros in Halo: The Flood.

Second Lieutenant is an entry-level rank for most commissioned officers. A Second Lieutenant usually receives a promotion to First Lieutenant after eighteen to twenty-four months of active service.

In informal settings, Second Lieutenants are referred to simply as "Lieutenant" or "LT".

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
Approximate insignia:
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	CPT	Maj	LtCol	Col	BGen	MajGen	LtGen	Gen
Navy:	ENS	LTJG	LT	LCDR	CDR	CAPT	RDML	RADM	VADM	ADM	FADM