Semi Powered Infiltration Armor

Semi-Powered Infiltration Armor, colloquially called "SPI Armor", was a armor system used by the UNSC. Though far more advanced than the ODST Body Suits, it was far less advanced than the MJOLNIR Armor. It was far less advanced and far cheaper. It was used by the Spartan-III supersoldiers. it features special photo-reactive panels that mimic the surrounding textures, effectively the UNSC equivalent to the Covenant Active Camoflague systems.

SPI Mark I
SPI Mark I was used by the Spartan-IIIs of Alpha and Beta Companies from 2531 to 2545. It featured hardened plates and photo-reactive panels. Though advanced, it could only take a few glancing blows before failing.

SPI Mark II
SPI Mark II was used at first by the Drill instructors for Gamma Company, then by Gamma Company themselves. SPI Mark II was a more advanced version of the armor, with numerous upgrades.