SPARTAN-III Alpha Company
- "I am going to give you a chance to learn how to fight, a chance to become the best soldiers the UNSC has ever produced, a chance to destroy the Covenant. I am giving you a chance to be like me: a Spartan."
- —Lieutenant Kurt Ambrose
Alpha Company was the first company of SPARTAN-IIIs to be trained. This group originally had 497 trainees recruited between the ages of four, five and six years old, but only 300 of them became SPARTAN-IIIs. The children were orphaned by Covenant attacks on various colonies such as Jericho VII, Harvest, Biko, and Eridanus II. When they were found, all of them joined to exact revenge on the Covenant.
From the moment they arrived on the planet Onyx, they were tested. That night they were instructed to paradrop to the designated pickup location. On December 27, 2531, they then began their training at Camp Currahee on Onyx, instructed by Lieutenant Commander Kurt Ambrose; in reality, Ambrose was Kurt-051, a SPARTAN-II who had been kidnapped in order to oversee the SPARTAN-III program. Their aggression levels were extreme, and ONI had concerns that the children would kill each other during training. Despite this, Alpha Company was declared active in late 2536.
They quelled an insurrection on Mamore, participated at the Battle of New Constantinople, battles in the Bonanza asteroid belt and the Far-gone colony platforms, along with six other engagements. However, nearly every single one of them died during Operation: PROMETHEUS, although they destroyed a massive Covenant shipyard in the process.
Before Operation: PROMETHEUS however, Kurt and Mendez hand-picked an unknown number of candidates that stood out from the rest and removed them from the company, assigning them to other units. They were also issued with more advanced equipment such as MJOLNIR armor to make their battlefield prowess comparable to that of the SPARTAN-IIs. These individuals included Emile-A239, Carter-A259 and Jun-A266, but their overall number is unknown. These Spartans also later served in a special operations unit known as Noble Team, along with candidates originally removed from Beta Company.
Individuals who failed to pass training became drill instructors for Beta Company; these washouts were particularly ruthless to the trainees, due to their regrets of not passing the test for the original Alpha Company.
 Operational history
Following Alpha Company's activation in 2531, its members took part in several battles. After its deployment, Alpha Company quelled an insurrection on Mamore. At other points in its history, Alpha Company won the Battle of New Constantinople and performed successful operations in the Bonanza asteroid belt and the Far-gone colony platforms. Alpha Company also participated in six other battles during this time.
 Operation: PROMETHEUS
- Main article: Operation: PROMETHEUS
The SPARTAN-IIIs were sent to the Covenant-controlled asteroid K7-49 to disable as many reactors possible so that the liquid contents of the facility would solidify and permanently clog their capacity to produce the metal.
Initial resistance to the Spartans were light, and they managed to disable two reactors before the Covenant could properly arrange a proper counterforce. The counterforce was neutralized, and the Spartans managed to destroy thirteen more reactors. By then, Covenant had sent in a massive army from orbit. The Spartans were cut off from their extraction craft, which caused the death of all of them. PROMETHEUS was a bitter-sweet success, the facility was permanently disabled, but all participating members of Alpha Company were completely wiped out.
 Known members
 List of appearances
- ^ a b c Halo: Ghosts of Onyx, page 81
- ^ a b Halo: Ghosts of Onyx, page 88
- ^ Halo: Ghosts of Onyx, page 69
- ^ Halo: Ghosts of Onyx, page 71
- ^ Halo: Ghosts of Onyx, page 67
- ^ Bungie.net: Communique from Kurt to Mendez
- ^ Halo: Ghosts of Onyx, "Chapter 9", page 89 ("There were 418 candidates, and only three hundred slots. Not all of them could be Spartans.")
- ^ a b c Halo: Ghosts of Onyx, pages 81-83