Sigma Team, also known as Sigma-Alpha, was a group of SPARTAN commandos recruited under the top-secret Project SIGMA, that served during the Human-Covenant War. Sigma Team operated in secrecy for several decades under the control of ONI. The team fought on many worlds between 2525 and 2552, being vital in many UNSC victories, and lessening the cost of defeats where they served. The team remained unbreakable throughout most of the war, and despite being from a program made secret even from Halsey's Reach-trained SPARTAN's ended up playing a major role in a number of battles. Sigma remained active following the end of the war, albeit under the UNSC Navy's command instead of joining the Spartan branch.
Conscription & Training
In 2517 the future SPARTAN-II's were selected following a vaccination program across the colonies, with 150 potential candidates identified by the Office of Naval Intelligence. However, only half could be chosen due to budgetary reasons, and after being kidnapped they were taken to Reach for training. Despite this, ONI still continued to monitor on the remaining seventy-five and following some convincing, allowed for twenty other children to be abducted and trained on Earth in secret. This was Project SIGMA. The children were rigorously indoctrinated and educated under the command of ONI's Doctor Calvin Roe and were taught the art of combat, military strategy, and survival by various drill instructors and Lieutenant Colonel Richard Mack, a famed special forces hero. Over the course of eight years, these children would be moulded into Humanity's finest soldiers much like their Reach-trained counterparts, forming bonds of camaraderie as they surpassed all expectations. Unlike those brought up as part of Catherine Halsey's program, the trainees within SIGMA were destined to serve under the direct command of the Office of Naval Intelligence to perform tasks no other soldiers or agents could accomplish, leaving the other SPARTAN-II's to undertake the monumental task of crushing Human Insurrection.
At the age of fourteen in 2525, the SIGMA Spartans would go through a series of biological augmentation procedures identical to the ones those trained on Reach went through, albeit with the knowledge learned from the mistakes made in augmenting Doctor Halsey's group. After it was discovered that far fewer SPARTAN-II's from the Reach group had survived the procedures intact, the decision was made to use eleven of these Spartans - Sigma-Alpha - to assist in their fight against the Insurrection. Sigma-Alpha was told that the rest of their comrades had died during their procedures as a result. In reality, no deaths had occurred despite the heavily weakened state many augmentees were left in. Several weeks afterwards, two of the Spartans, Jack-085 and Ahmad-126, escaped their training facility and went on the run. Ahmad supposedly killed himself when he was cornered and Jack disappeared, not to be seen again for many years.
In 2526, the nine remaining members of Sigma-Alpha were sent on their first mission to the colony world, Gallis, where there was heavy fighting with rebels. Their mission was to secure nuclear warheads that the rebels were threatening to use, and to rescue hostages. The team had a successful mission, wiping out the Insurrectionists. However, they discovered that there were no hostages; the rebels had been bluffing. The team were also not able to capture their elusive leader, who left a message mocking the Spartans, and an explosive trap that nearly killed Marco-025.
The Human-Covenant War
Sigma Team served in many different operations during the Human-Covenant War, and was always able to accomplish the mission no matter what. They fought on many world, many battlefields and always got out alive, never leaving a teammate behind. However, in 2550, that all changed in a massive engagement against Insurrectionists, that brought the team it's first two casualties, and a brush with a former member. Two years later, in early 2552, Sigma Team was stationed on the colony world of Harpa when it was attacked by Covenant forces. Sigma Team took two more casualties there, also losing Mack Sr. With a badly damaged ship, they were barely able to escape to Reach. Several months later, during an evacuation of a colony world, another member of the team, Resk-063, gave his life trying to save thousands of civilians from Covenant forces. This would be the third SPARTAN lost in a single year.
The Fall of Reach
Sigma arrived on Reach mere days before the main attack. As they were heading to an outpost via Falcon, they received a distress call from Tau Team, who had been attacked while investigating one of many communication arrays that went down across the planet. The team were surprised to find a Covenant attack force there, and managed to wipe out their foes, returning to command just as WINTER CONTINGENCY was declared by HIGHCOM following an attack on the Visegrad relay. Not long after, Spartan teams Sigma, Upsilon, Tau and Noble were deployed in a large counter-attack against Covenant landing forces in the area. Though successful on the ground, the UNSC were put into full retreat following the reveal of a cloaked Supercarrier above the battlefield. Following Operation:UPPER CUT, Sigma, accompanied by Tau Team, were sent on a mission, Codenamed Operation: DROPKICK. This was a follow-up to UPPERCUT. The team were to board and destroy a Covenant Supercarrier about to go into Reach's atmosphere. The Mission was successful, but at the cost of Frank-A103 and Dom-A178.
Not long after, they were deployed to New Alexandria to Evacuate a VIP, Dr. Calvin Roe, the man who had them kidnapped and trained. However, as the three teams got to the building the Doctor was in, they came under heavy attack by Covenant forces. Wulf-041, Dan-A105, Eugene-
A133 and Chris-A189 entered the building to clear out covenant forces and extract the VIP, while the others provided covering fire from Falcons. However, Dr. Roe only needed the Spartans' assistance to provide cover for his escape, and detonated the building, killing Wulf and the others. As Roe sped away, Kane-099, as the ranking Officer, ordered the Spartans to pursue him out of New Alexandria.
Leaving the city mere hours before it's final glassing, They pursued Roe to Outpost Foxtrot Whiskey. As they approached, several banshees began pursuing them. Dr. Roe, knowing that the Spartans were chasing him, landed, and killed his ODST bodyguard, taking his armour.
He then ordered the several Rocket Warthogs stationed on a cliff side to fire upon the approaching Falcons, saying that they had been seized by the enemy. The warthogs unleashed a salvo that destroyed the lead Falcon, killing Sal-A142. The surviving falcons, still pursued by banshees, flew past, causing the warthogs to be destroyed by banshee fire. Upon landing at the base, The Spartans began looking for Doctor Roe, who attempted to board a warthog, but was stopped by Alex-A121. Roe attempted to run, but was quickly surrounded. Despite trying to reason with the Spartans, Roe was killed by Marco-025, for killing Wulf, Dan, Eugene and Chris.
Several hours later, more UNSC forces arrived at the base from New Alexandria. The last group warned the Spartans that Covenant forces were on the way. Rallying the troops, Kane-099 devised a plan: He and Martin-A136 would stay at base along with snipers to provide cover. Jax-007 would lead a tank-led charge along the right flank, while Marco-025 led infantry up the left. If things were going badly, they would use their Falcons to escape the base. Eventually, a large enemy force arrived not far away from the outpost. Wraiths bombed the area, and squads of elites began charging in. With heavy losses, the Spartans held their own until several enemy Ghosts and Revenants arrived. By this time, Kane-099 had joined the fight up front. He was almost killed by a Revenant had it not been for Dorian-A188, with a Dropshield. As they began to push towards the hill, Dorian was killed by a Plasma launcher. Marco-025 also used Armour Lock to save himself. Eventually pushing through a cave, the Spartans were able to wipe out the last covenant forces on a small island, winning the battle.
Back at the base, Martin-A136, whose wounds had been temporarily healed with Biofoam, intercepted communications from the UNSC Pillar of Autumn, about their preparations to leave the plane, and that any remaining UNSC forces should join them soon. when the others arrived, Martin told them the news, and they flew towards the shipyard. When they arrived, however, the Pillar Of Autumn had only just left, leaving behind a large amount of Covenant, most of whom began to head towards Sigma's location.After checking a terminal Kane-099 saw that there was a single Frigate left nearby: The UNSC Bright New Day.
To slow the Covenant down, Jax-007, Nelson-A122, Jordan-A111 and Alex-A121 volunteered to stay behind and hold them off until the frigate was in the air. Kane-099, Marco-025, Martin-A136 and Louie-A199 travelled to the frigate, where they met up with the survivors of Whiskey-04. In the ensuing battle, both Jordan and Nelson are killed. Jax and Alex managed to commandeer two banshees and fly into the frigate's vehicle bay. The Bright New Day was able to escape Reach as it was being glassed.
Return to Earth
After some time, the Spartans returned to Earth to find it under attack by Covenant forces. So, Kane decided to set the ship on a collision course with a nearby Covenant cruiser as it came towards Earth. At the last moment, the ODST's and Spartans launched the Frigate's SOEIV's, falling to Earth moments before the Day impacted and destroyed the enemy ship. The team landed on the outskirts of Moscow, Russia, where they fought a bloody battle before returning to PILLAR base, which would serve as their base of operations for the next few months. The SPARTAN-II's and III's split up during the Battle of Earth and fought across the globe until the war finally ended in early 2553.
Following the end of the Human-Covenant War, Sigma Team was split up once more. Martin and Louie were reassigned to solo operations by ONI against pockets of Covenant resistance in the rebuilding Outer Colonies, while Alex was placed in charge of a Remote Contact Team for some time. While the Spartan Branch had been created to accommodate the SPARTAN-IV Program, Sigma Team remained under the UNSC Navy's jurisdiction and continued the fight against Covenant and Insurrectionist targets for the next few years.
Despite their losses in the war's final years, the three Spartans showed no signs of slowing down and welcomed the opportunity to return to duty after their brief reprieve at the end of the war. They would continue to serve with distinction as new threats emerged in the post-war galaxy. They would go on to fight not only against the large Covenant faction serving under Jul 'Mdama, but also terrorist groups such as the New Colonial Alliance and True Vanguard. Following the discovery of Requiem in 2557, Sigma sound found themselves deployed to numerous freshly-discovered Forerunner sites as Promethean constructs began to appear alongside Covenant foes. By October of 2558, Sigma's three members were stationed in the Inner Colonies on ONI's orders under the pretence of assisting newly-recruited SPARTAN-IV's during their post-augmentation retraining.