ORIGINS:
The SPARTAN IV program was the fourth iteration of the SPARTAN supersoldier projects. Like the original ORION project, the SPARTAN IV program utilized adult candidates rather than conscripting children. The volunteers were from other branches of the UNSC, particularly experienced members of the Orbital Drop Shock Troopers from the UNSC marine corps. The program went active as early as January 7, 2553.

AUGMENTATION PROCEDURES:
Like the augmentation procedures performed on SPARTAN II candidates and the improved procedures performed on SPARTAN IIIs, the SPARTAN IV augmentations were the most improved iteration at the time. Generating similar (albeit slightly inferior) physical results as the previous SPARTAN II generation with the 0% mortality rate of SPARTAN III candidates, the programs perhaps most successful element was that it no longer required the conscription of abducted children. The procedures had improved to such an extent that adult volunteers could go through the process with no risk of death or injury. Despite this, candidates were required to meet exceedingly strict physical requirements to be able to undergo the process.

HISTORY:
As stated before, the program went active in early 2553 where the first batch of candidates were successfully deployed on missions that were too high-risk for even ODST troopers. The aim of the project was to produce both the results of the SPARTAN II and III generations. As such, the MJOLNIR GEN2 line of armours were produced. The program as a whole fixed the many issues with previous generations. Namely, while the SPARTAN IVs augmentations increased the candidates' abilities to superhuman level, they were still not on par with the IIs and IIIs. However this fixed the ethical issues of mortality rates and the need to conscript children into the program.

Their inferiority in strength compared to the previous generations was made up for by the GEN2 line of MJOLNIR armours. These suits were stronger, more durable, lighter and most of all, cheaper to produce than the GEN1 armours which costed as much as a small space ship to make. A SPARTAN IV clad in MJOLNIR GEN2 armour had enough potential strength to go toe-to-toe with a SPARTAN II in GEN1 armour, theoretically. Furthermore, the 0% mortality rate meant that SPARTAN IVs could be mass produced like the SPARTAN IIIs were. As such, around 800 SPARTAN IVs were produced by 2555.

Production was discontinued on March 16, 2555 due to high costs generated by the program but also lack of need for any more SPARTAN IVs. Each SPARTAN was assigned to different Fireteams with their own leaders and sent off to high-risk missions deep in enemy lines. The success rate of these teams were near 100% with reports of SPARTAN IVs going KIA were rare, if at all.

The re-emergence of supernatural threats, namely The Apocalypse, Draetheus's army of Hyper-Soldier Shock Troops and the subsequent Demonic Crusade, as well as a new Covenant Faction lead by Rha 'Mantakree yielded the first major casualties in the program. Faced with stronger enemies than before, SPARTAN IV training regimes became more strict but casualties continued to increase, albeit at a slower rate.

However the greatest disaster to ever afflict the program was the Battle of Haven. The battle and its continuous growth over the years caught the full attention of the UNSC and by late 2558, 300 SPARTAN IVs were deployed to the Shield World to fight for control over it against Rha Mantakree's Covenant faction. This resulted in one of the biggest disasters in Human history, with mass casualties spanning both armies. Marine forces on the planet were completely decimated later on in the conflict and during the final stand, only a few SPARTAN IVs remained to stand the UNSC's ground on the planet. By the end of it, around 290 SPARTANS were rendered KIA.

As of September 2564, only 30 SPARTAN IVs remain in active service.