The SPARTAN Program
The Spartan program started with Project ORION or the Spartan-I program as it is called was the first phase of the Spartan Program. It was initiated in 2491 to test genetic enhancements on volunteers from the UNSC. Despite that there was a high mortality rate, the ORION Project was successful to actually warrant the Spartan-II Program. The only known soldiers that underwent Project ORION are James Lee, Gilly, Morales, Gladys Swanson, and Avery Johnson.Catherine Halsey. The newly developed Spartan-II's were the first to meld Advanced Exoskeleton technology with the soldier's superior physiques.
The SPARTAN-II candidates after being sedated were taken to the colony world Reach, and began their training under Chief Petty Officer Mendez. To marginalize the civilian lives they had once led, their names became a combination of their given names and a number, with family names being discarded. The SPARTANs endured a great deal of hardship during their first years of training: they were placed into situations and drills that pushed their abilities to their very limit and beyond. Their hard training was complemented with high-level education, which included mathematics, science, reading, writing, and military tactics. Although his training methodology was tough, even brutal in some regards, Chief Petty Officer Mendez always instilled discipline, honor, and respect into the SPARTANs. He taught the SPARTANs how to kill, but at the same time he taught them the difference between right and wrong. Mendez trained the SPARTANs until 2525 when, at the age of fourteen, they would go through the toughest part of their training: the biological augmentation procedures, which would kill 30 of the 75 conscripted children and cripple 12 others who would "wash out" of the SPARTAN-II program, going on to join the Office of Naval Intelligence; only 33 survived the procedures with no physiological deformities. The bodies of those candidates who died were placed in cryo-suspension, in the hope that they could some day be resuscitated. At least some of the candidates who were crippled were eventually rehabilitated. Several elements of the candidates' training were kept secret from Halsey that only Professor Agnes and Professor Mike (who worked on the project with her) knew about.
The Human-Covenant war marked a change in objectives for the program; originally intended to quell rebellions, the SPARTANs were now forced into battle against a superior opponent to the Insurrectionists: the Covenant. This new threat accelerated the SPARTANs' training to its final phase: Project MJOLNIR. With the Mjolnir Armor, the SPARTANs would be the first major UNSC response to the alien threat. The SPARTANs continuously proved highly effective against all threats; their heroic rearguard and delaying actions saved countless human lives from the genocidal Covenant onslaught. Their prowess was well known among the Covenant, who came to fear the SPARTANs as Demons. In 2547, the SPARTAN-II program was revealed to the public in an effort to boost morale among the UNSC.Inevitably the small number of SPARTAN-IIs dwindled as casualties were sustained. As the exploits of the SPARTANs were a major propaganda boom to the UNSC, Section II of the Office of Naval Intelligence issued Directive 930, which stated that SPARTANs killed or wounded would be listed as "Missing in action" (MIA) or "Wounded in action" (WIA), thus maintaining the illusion of the SPARTANs' invincibility. In late 2552, all except three of the remaining active SPARTANs rendezvoused at Reach to receive new orders for Operation: RED FLAG, an operation that HIGHCOM hoped would end the war. They would commandeer a Covenant vessel, locate the Covenant homeworld, and return with captured Covenant leadership to force a ceasefire. The Artificial intelligence construct Cortana, carried within John-117's Mjolnir Mark V powered assault armor, would serve as the strike force's hacker and technology specialist. However, all preparations were interrupted and subsequently canceled by the Covenant's invasion of Reach. In the ensuing disaster, most of the SPARTAN-IIs were killed, although some took shelter in ONI's CASTLE Base. Two escaped aboard the UNSC Pillar of Autumn, one of whom was place in cryostasis aboard the ship after sustaining life-threatening injuries during the battle on Gamma Station. The Pillar of Autumn soon arrived at Halo Installation 04, which John-117 ultimately destroyed to prevent the spread of the Flood. Following the Battle of Installation 04, the survivors returned to Reach and were able to rendezvous with the remaining SPARTANs. The survivors then carried out a raid that resulted in the destruction of a Covenant fleet anchorage, stalling a Covenant plan to invade Earth. SPARTAN-IIs would go on to play pivotal roles in the Battle of Earth, the Battle of Installation 05, the Battle of Onyx, and the Battle of Installation 00.Beta-5 Division of the Office of Naval Intelligence's Section-III in order to produce cheap and expendable super soldiers to fight for the survival of humanity and the United Nations Space Command's colonies.
The SPARTAN-III program was both the successor and supplement to the SPARTAN-II program. Created and engineered by Colonel James Ackerson of the Office of Naval Intelligence, the SPARTAN-III soldiers were to be the next generation of supersoldiers. Composed primarily of vengeful orphans from fallen colonies, they would be cheaper to arm, train, and produce; being chosen from a wider pool of candidates, they would also be more numerous than their SPARTAN-II predecessors. They would rely on superior battle tactics, teamwork and sheer numbers rather than advanced technology, special augumentation, and equipment, to achieve their effectiveness.
The SPARTAN-II program had been a dazzling success for the UNSC. Tales of Spartan super soldiers fighting off thousands of Covenant attacks had become the stuff of legend. Unfortunately, there were too few SPARTAN-IIs to turn the tide of the war. Even worse, the director for the program, Dr. Catherine Halsey, had postponed the training of new Spartan-IIs for years due to the extremely specific genetic requirements for the children to be selected.The SPARTAN-II program also had several problems and deficiencies which overshadowed its success to ONI. Firstly, the high mortality rate of the children during augmentation was counter-productive to the purpose, drive, and ambition of the program. Next, funding the Spartan program, including their training and Mjolnir Armor, cost as much as a Battle Group, at least according to Rear Admiral Ned Rich. Third, there were far too few of them for them to turn the tide of the war. Finally, the Spartan-II program had gone public to improve morale in 2547. Even though it was a huge morale boost to the UNSC, it was a problem for most of the Office of Naval Intelligence. ONI operated in secrecy, and anything that shone light on their operations was seen as detrimental to their efforts. The SPARTAN-IIIs were designed to be better trained, cheaper, and expendable. They would be trained in companies of 300 to 330 at a time, and then sent on suicide missions that the UNSC could not accomplish even with the elite Orbital Drop Shock Troopers. Though the casualty rates of the SPARTAN-IIIs stood at 100 percent on some missions, to ONI, all the operations were strategic successes. They were trading lives for time against the larger and technologically superior Covenant Empire. ONI hoped that in time, enough Spartans would survive to train more and more future Spartans, swelling the ranks of available super soldiers from only thirty SPARTAN-IIs in 2531 to a hundred thousand SPARTAN-IIIs within ten to twenty years.
The SPARTAN-IV Program is the fourth generation of the SPARTAN program, and unlike stages II and III it consists of members recruited from the UNSC's military augmented to be capable of wearing a variant of the Mjolnir armor. This phase was initiated by Admiral Margaret Parangosky after the Human-Covenant war, and some are stationed near the UNSC Infinity in the Oort Cloud.Similar to the original ORION Project, the SPARTAN-IV Program would only consist of adult volunteers, as opposed to young children. When the Program was started, the surviving members of the previous generations were offered to be integrated into it, though it's unknown how many exactly accepted/declined. The first active SPARTAN-IVs were already deployed by 2553, as some of them were temporarily assigned to the UNSC Infinity before it was scheduled to launch.
So far there have been 3 SPARTAN-IV Teams confirmed to be in Halo 4 Majestic Squad, Shadow Squad, and Fireteam Crimson, which all are said to interact with the Chief during the campaign.