The rank structure of the United Nations Space Command's mainline branches of service (the Navy, the Marine Corps, the Army, and the Air Force) is largely derived from the system employed by the 21st century United States military. Spartan Operations is an exception to this as its members lack conventional ranks.

Enlisted ranks

Air Force

Pay grade	E-1	E-2	E-3	E-4	E-5	E-6	E-7	E-8	E-9
Insignia/Title	Airman Basic (AB)	Airman (Amn)	Airman First Class (A1C)	Senior Airman (SrA)	Staff Sergeant (SSgt)	Technical Sergeant (TSgt)	Master Sergeant (MSgt)	Senior Master Sergeant (SMSgt)	Chief Master Sergeant (CMSgt) Command Chief Master Sergeant (CCM)

Army

Pay grade	E-1	E-2	E-3	E-4	E-5	E-6	E-7	E-8	E-9
Insignia/Title	Private (Pv1)	Private (Pv2)	Private First Class (PFC)	Specialist (SPC) Corporal (CPL)	Sergeant (SGT)	Staff Sergeant (SSG)	Sergeant First Class (SFC)	Master Sergeant (MSG) First Sergeant (1SG)	Sergeant Major (SGM) Command Sergeant Major (CSM)

Marine Corps

Pay grade	E-1	E-2	E-3	E-4	E-5	E-6	E-7	E-8	E-9
Insignia/Title	Private (Pvt)	Private First Class (PFC)	Lance Corporal (LCpl)	Corporal (Cpl)	Sergeant (Sgt)	Staff Sergeant (SSgt)	Gunnery Sergeant (GySgt)	Master Sergeant (MSgt) First Sergeant (1stSgt)	Master Gunnery Sergeant (MGySgt) Sergeant Major (SgtMaj)

Navy

Pay grade	E-1	E-2	E-3	E-4	E-5	E-6	E-7	E-8	E-9
Insignia/Title	Crewman Recruit (CR)	Crewman Apprentice (CA)	Crewman (CN)	Petty Officer Third Class (PO3)	Petty Officer Second Class (PO2)	Petty Officer First Class (PO1)	Chief Petty Officer (CPO)	Senior Chief Petty Officer (SCPO)	Master Chief Petty Officer (MCPO)

Officer ranks

Pay Grade	Title	Insignia
O-1	Air Force: Second Lieutenant (2nd Lt) Army: Second Lieutenant (2LT) Marine Corps: Second Lieutenant (2ndLt) Navy: Ensign (ENS)
O-2	Air Force: First Lieutenant (1st Lt) Army: First Lieutenant (1LT) Marine Corps: First Lieutenant (1stLt) Navy: Lieutenant, Junior Grade (LTJG)
O-3	Air Force: Captain (Capt) Army: Captain (CPT) Marine Corps: Captain (CPT) Navy: Lieutenant (LT)
O-4	Air Force: Major (Maj) Army: Major (MAJ) Marine Corps: Major (Maj) Navy: Lieutenant Commander (LCDR)
O-5	Air Force: Lieutenant Colonel (Lt Col) Army: Lieutenant Colonel (LTC) Marine Corps: Lieutenant Colonel (LtCol) Navy: Commander (CDR)
O-6	Air Force: Colonel (Col) Army: Colonel (COL) Marine Corps: Colonel (Col) Navy: Captain (CPTN)
O-7	Air Force: Brigadier General (Brig Gen) Army: Brigadier General (BG) Marine Corps: Brigadier General (BGen) Navy: Rear Admiral (Lower Half) (RDML)
O-8	Air Force: Major General (Maj Gen) Army: Major General (MG) Marine Corps: Major General (MajGen) Navy: Rear Admiral (Upper Half) (RADM)
O-9	Air Force: Lieutenant General (LtGen) Army: Lieutenant General (LTG) Marine Corps: Lieutenant General (LtGen) Navy: Vice Admiral (VADM)
O-10	Air Force: General (Gen) Army: General (GEN) Marine Corps: General (Gen) Navy: Admiral (ADM)
Special	Air Force: General of the Air Force (GAOF) Army: General of the Army (GA) Marine Corps: N/A Navy: Fleet Admiral (FADM)

Warrant officer

A warrant officer is a military officer in the Armed Forces ranking above a non-commissioned officer (NCO), but below a commissioned officer. Warrant officers are technical specialists and subject matter experts that are awarded an officer's commission in recognition of their expertise and leadership role. They take the officer's oath of service and are rated above enlisted soldiers, though remain subordinate to full officers. The rank structure of warrant officers consists of two ranks, as follows:

• Warrant officer (WO): With the rank code of WO-1, a warrant officer serves as a resident technical expert, and may serve as a crew chief or pilot in the UNSC Army.
• Chief warrant officer (CWO): With the rank code of WO-2, a chief warrant officer serves as a command advisor or or senior subject matter expert. In the UNSC Navy, they may be the captain of a utility ship.

Both the UNSC Navy and Army utilize warrant officers heavily, though they are rarely found in the Marine Corps. Both the Air Force and Spartan Operations are the only service branches that do not select or utilize warrant officers.

Trivia

• The Halo Encyclopedia erroneously describes the structure and insignia of the UNSC's ranking system as being identical to those used in Halo multiplayer, Halo 3 in the original printing and Halo: Reach in the 2011 edition.
• All Marine Corps ranks between Staff Sergeant and Sergeant Major are classified as Staff non-commissioned officers.