Semi-Powered Infiltration armor

The Semi-Powered Infiltration Armor, or SPI Armor, is an experimental armor system used by the United Nations Space Command. It was developed for the SPARTAN-IIIs.

Description
Though more advanced than the Orbital Drop Shock Troopers' ballistic body armor, it is far less advanced and less powerful than the MJOLNIR Powered Assault Armor used by the SPARTAN-IIs. Its main benefit is that it is drastically cheaper to produce than the MJOLNIR armor. The SPI armor was designed with an emphasis on stealth rather than on raw power. It features special photo-reactive panels that mimic the surrounding textures, effectively being the UNSC equivalent to the Covenant's active camoflauge systems. It has been described as part "legionnaire mail, part tactical body armor, and part chameleon" by both Tom-B292 and Dr. Catherine Halsey.

SPI Armor Mark I
The SPI Armor Mark I was used by the Spartan-IIIs of Alpha Company. It featured hardened plates and photo-reactive panels. Though advanced compared to standard UNSC infantry armor, it could only take a few glancing blows before failing.

SPI II armor
The SPI Armor Mark II was a more advanced version of the Mark I SPI, first used by drill instructors Company Beta, and then by the Spartans of Beta Company. They had photoreactive new coating to increase its camouflage properties. There were also numerous experimental reinstall the layers of ballistic gel, updating software packages, and other functions. Although the photo-reactive new coating could mimic a wide range of electromagnetic radiation, remained sensitive to overloading, so users will remain vulnerable for several seconds after you hit a flashbang or plasma panels, while the recovery.

It was proposed in 2537 for Alpha Company, but the request was denied because the armor was over budget. After pyrrhic victory Alpha Company in Operation: Prometheus, the Mark II armor SPI was approved for mass production. After increasing the company Gamma, minor adjustments were installed in the SPI Armor Mark II.

advantages
1. The armor is much cheaper and easier to mass produce the Mjolnir armor. 2. Includes photo-reactive panels that act as active camouflage to the user. 3. It is easier to transport, which is not as big or as strong as the Mjolnir armor. 4. The armor has an effective cooling system and is significantly more difficult to detect, even with thermal scanners. This system can fail during periods of extended use, however. 5. SPI armor users do not need a technician to help them get the armor. 6. The armor requires less physical increase compared with the armor MJLONIR, which allows users, in addition to SPARTAN-IIIs to operate armor.

Disadvantages
1. You do not have the energy shield system, unlike-II 'MJOLNIR Mark V and Mark VI SPARTAN models, making the user more vulnerable to enemy fire and a major contributor to the high mortality rate of SPARTAN-III. However, the SPARTAN-III headhunters are known to be equipped with energy shields for armor, due to its nature and value of elite. However, power must be extracted from energy shields to recharge module Camoflauge active demand, and current information indicates only the headhunters are equipped with shields. 2. Does not force improved SPARTAN-IIIS, speed or agility, as the MJOLNIR does for its users. 3. Since the reactive-picture boards time to recover after the explosions, like a flashbang grenade and hits the plasma, the SPARTAN-III is visible until the plates to recover. With the exception of headhunters' suits, not real armor SPI Camoflauge systems active. 4. It is made of a less dense alloy MJOLNIR armor: Holly Kelly-087-G003's dented plate chest with his fist in his first encounter with the SPARTAN-IIIs. 5. The SPI armor is not waterproof or airtight, unlike the Mjolnir armor. 6. The SPI armor can not be used for long periods of time without the cooling system fails. 7. The SPI armor has an air supply for only seven minutes, while the MJOLNIR has a supply of air for ninety minutes. 8. It lacks the ability to support on board an artificial intelligence construct, unlike the Mark V, Mark VI, and Black models in the Mjolnir armor.

==trivia* The safety helmet Halo: Reach has a striking resemblance to the SPI armor. * Some screenshots released by Bungie was speculated that fans would be able to use the SPI armor in Halo 3. However, the armor was later revealed to be the MJOLNIR EVA Variant.==