SPARTAN-III Gamma Company
Gamma Company is the third generation of the SPARTAN-III program. The company was formed around 2543 and was considered by Lieutenant Commander Kurt Ambrose to be comprised of "the finest Spartans ever."
Gamma Company was trained with the help of Tom-B292 and Lucy-B091, the only two known surviving SPARTAN-IIIs from Beta Company, as well as Senior Chief Petty Officer Franklin Mendez and candidates from the previous companies who had "washed out", becoming drill instructors for the later SPARTAN-IIIs. Not one of the 330 candidates opted out of the program, and at the request of Lieutenant Commander Ambrose, all 330 of those who passed the selection process were approved. 
Every candidate survived their training and augmentations. In addition, they were injected with illegal drugs that altered the frontal lobes of their brains to enhance aggression, strength, endurance, and tolerance to injury.  These Spartans received deployment orders only a few weeks after the Fall of Reach, and most left Onyx before the Battle of Onyx occurred. It is unknown where they were deployed.
Only fifteen Spartans of Gamma Company remained on Onyx for top honors competitions when the Battle of Onyx began. Of these Spartans, seven were Killed In Action, and eight escaped into the Shield World. Of the eight survivors, five are now trapped in Forerunner Slipspace field pods, which hold their bodies in both Slipspace and normal space, but keep the bodies inside perfectly safe, a technologically superior counterpart of the human cryo-chamber.
 Battle of Onyx
- Main article: Battle of Onyx
At 0645 hours on October 31, 2552, three five-member teams from Gamma Company were competing for top honors when they experienced a disturbance in the ground. Moments later, Team Saber witnessed a large explosion near them, and saw what they thought was a "drone". When the drone appeared to have shields, they assumed that it was a Covenant force and alerted the two other teams, Gladius and Katana.
Meanwhile, Lieutenant Commander Ambrose desperately tried to contact the Spartans, but was unable to find them; he then went to the armory to procure heavy weapons.
As Team Saber were attacking the drones, which were actually Forerunner Sentinels they discovered that the constructs could only track high-velocity objects, such as bullets. As a result, they began using large rocks to destroy them. They later rendezvoused with Ambrose, Mendez, SPARTAN-II Blue Team, and Dr. Catherine Halsey. Team Gladius had been found KIA and Katana had not yet been discovered.
Dr. Halsey informed the Spartans that the drones were not of Covenant origin; instead, they were Sentinels which had been made by the Forerunners. Their appearance was somehow linked to John-117's destruction of Installation 04. She also stated that there were Forerunner "treasures" in the core of the planet.
The Spartans then assembled made their way to the core, losing Dante-G188 in the process, as the Covenant had discovered the planet. Then, they decided to destroy the majority of the Sentinels by destroying the "factories" they came from. When they succeeded, they traveled to the entrance to the core and discovered Team Katana in "pods". The pods were a Forerunner device that kept them perfectly safe, but the Spartans did not know how to deactivate them.
Kurt and the Spartans made a last stand on the entrance, with two FENRIS warheads to act as a fail-safe in the case that they were killed. The Covenant then began to assault them with a massive army. In the fighting, Holly-G003 was killed. As they began to run out of ammo, they went through the portal to the core. The rest of Team Saber survived and went inside the portal, where they were accepted into Blue Team.
 Known Members
- Team Gladius - KIA
- Team Katana - WIA
- Team Saber
Just like Beta Company, Gamma Company was equipped with the SPI Armor/Mark II. During the initial stages of the Battle of Onyx, they were primarily armed with rubber rounds as a result of their practice fighting.
- Main article: Project CHRYSANTHEMUM
Gamma Company received the same biological enhancement procedures as Alpha and Beta companies. However, frustrated with the deaths of his previous two classes of Spartans, Kurt-051 added the following illegal drugs to their augmentation procedures:
- 009762-OO: A mutagen that alters key regions of the subject's frontal lobe. Enhances aggression, strength, endurance, and tolerance to injury. Kept in check by the antipsychotic and bipolar-integration drugs.
- 009927-DG: Miso-olanzapine. An antipsychotic. Counters the mutagen's properties.
- 009127-PX: Cyclodexione-4. A bipolar-integration drug. Counters the mutagen's properties.
This was against the recommendation of Deep Winter, Onyx's smart AI. Thus Kurt removed all traces and documents regarding the drugs.
 List of appearances
- ^ Halo: Ghosts of Onyx, page 98
- ^ Halo: Glasslands, page 435
- ^ Halo: Ghosts of Onyx, page 98
- ^ Halo: Ghosts of Onyx, pages 99-100
- ^ Halo: Ghosts of Onyx, page 102
- ^ Halo: Ghosts of Onyx, page 114