Project REX, officially designated SPARTAN-II Experimental Subproject-S88, was one of the many classified projects commissioned by the United Nations Space Command during the war. A subproject of the Spartan-II Program, REX was a project ostensibly aiming to boost the augmented capabilities of the UNSC's remaining Spartan-IIs in a attempt to further increase their combat-effectiveness against the Covenant who were now laying siege to the Inner Colonies. But the project also had an ulterior goal, one in creating a Spartan-II capable of countering the other Spartan-IIs should they become rogue.