- "There won't be any program; not like the Spartan-Twos, anyway or the Spartan-Threes, if I can help it. We're back to using consenting adults now, like we did in Project Orion."
- —Margaret Parangosky
Commissioned as a result of the success of the preceding SPARTAN-II and SPARTAN-III projects, the SPARTAN-IV Program was originally to be headed by SPARTAN-III lead Colonel James Ackerson, with SPARTAN-II project lead Dr. Catherine Halsey to be reassigned as Ackerson's subordinate. Ackerson was killed following the Battle of Mare Erythraeum and Halsey was arrested after returning from Onyx, though ONI continued the program without the two.
Like the original ORION Project, the SPARTAN-IV Program utilizes consenting adult volunteers selected from the other branches of the UNSC Defense Force. Recruits are drawn from both career military veterans and young soldiers who show considerable promise. The SPARTAN-IIs and SPARTAN-IIIs who survived the Human-Covenant War were offered to be integrated into the SPARTAN-IV Program. An unknown number of SPARTAN-IVs were active by 2553. Some of them, including Fireteam Majestic, were assigned to the UNSC Infinity before it was launched. They trained with one another on the Infinity's state-of-the art combat deck (a training chamber that is capable of replicating environments), in order to constantly stay battle-ready.
The SPARTAN-IVs serve in a dedicated branch of the UNSCDF known simply as "Spartan", whereas their forebears operated within other chains of command. Unlike their predecessors, the SPARTAN-IVs are identified by their surnames rather than numeric tags (due to their obvious volunteered enlistment rather than kidnapping/conscription). Unusually, the SPARTAN-IVs have shown a great deal of solidarity, especially impressive given the short time they have served together. Many of them have adopted colloquialisms first used by the SPARTAN-IIs, such as "Alpha Bravo" for "Alien Bastard". Psychologists assert that this camaraderie and cohesiveness will help distinguish the SPARTAN-IVs, and the Spartan branch as a whole, from the other UNSCDF branches.
 List of Spartan-IV units
|UNSC Infinity Spartan command||Active|
|Gypsy Company||Active||At least two Spartan-IVs||Also contains UNSC Marine Corps personnel.|
|Mountain Squad||KIA||A science attache unit. Killed during the Requiem campaign after being shot down in Two Giants.|
|Fireteam Apex||Active||unknown||Participated in the Requiem campaign|
|Fireteam Avalanche||Active||unknown||Participated in the Requiem campaign|
|Fireteam Castle||KIA||Killed in action after being shot down during the Requiem campaign|
|Fireteam Crimson||Active||Four Spartans|
|Fireteam Domino||Active||unknown||Participated in the Requiem campaign|
|Fireteam Forest||Active||Aided Crimson in acquiring replace power supply for the Harvester|
|Fireteam Horse||Active||unknown||Participated in the Requiem campaign|
|Fireteam Ivy||Active||unknown||Participated in the Requiem campaign|
|Fireteam Kodiak||Active||unknown||Participated in the Requiem campaign|
|Fireteam Lancer||Active||Participated in the Requiem campaign|
|Fireteam Rhino||Active||unknown||Participated in the Requiem campaign|
|Fireteam Shadow||Active||Participated in the Requiem campaign|
|Fireteam Sword||Active||unknown||Participated in the Requiem campaign|
|Fireteam Switchback||Active||Captured during a mission to destroy a Harvester during the Requiem campaign Later rescued by Fireteam Crimson and Fireteam Lancer.|
|Fireteam Sydney||Active||unknown||Participated in the Requiem campaign|
|Fireteam Talon||Active||unknown||Participated in the Requiem campaign|
|Fireteam Tower||Active||unknown||Participated in the Requiem campaign|
|Fireteam Wolf||Active||unknown||Participated in the Requiem campaign|
 MJOLNIR Armor
- Main article: MJOLNIR Powered Assault Armor (GEN2)
 Augmentation procedures
Like the augmentations performed for the SPARTAN-IIs and the improved procedures utilized in the subsequent SPARTAN-III Program, the SPARTAN-IVs underwent a series of enhancement procedures in order to wear MJOLNIR armor.
A SPARTAN-IV from Making Halo 4: First Look.
 List of appearances
- Halo: Glasslands (First mentioned)
- Halo: The Thursday War (Mentioned only)
- Halo 4 (First appearance)
- ^ a b YouTube: Halo 4 Flag Stabbing and Spartan Cosplay - Comic-Con 2012
- ^ a b Halo: Glasslands, page 434
- ^ Halo: Glasslands, page 147
- ^ a b Halo: Glasslands, page 422
- ^ a b Eleventh Hour reports, part 3
- ^ Halo: Glasslands, page 435
- ^ a b Gameinformer (May 2012), pages 46-47
- ^ a b Halo 4 Official Site: Story
- ^ a b YouTube - Halo 4: Spartan Ops Gameplay
- ^ a b Halo 4, level Reclaimer
- ^ a b c d Spartan Ops, S1E3 Spartan Mountain
- ^ a b c d e f g h i j k l m n o p q r Halo 4 Limited Edition — War Games Session Summary
- ^ Spartan Ops, Episode 7, Chapter 2: "Home Field"
- ^ Spartan Ops, S1E1 Departure
- ^ Spartan Ops, S1E4 Didact's Hand: Chapter 1: Hairy Call
- ^ Spartan Ops, Episode 10, Chapter 3: "Seize the Power"
- ^ Spartan Ops, Episode 7, Chapter 4: "The Guns of Infinity"
- ^ MightyApe.co.nz: Halo 4 Limited Edition screenshots
- ^ YouTube - Halo 4: Spartan Ops - Episode 6 Chapter 4 Developer Commentary
- ^ Spartan Ops, S1E8 Expendable: Chapter 3: Lancer
- ^ Halo 4, Infinity