SPARTAN-IV

The premise behind the SPARTAN-IV program was simple: use technology developed for the SPARTAN-I and SPARTAN-III programs and meld that with the best qualities of the SPARTAN-II education program. The result would be a new breed of Spartan that could be recruited from the best and brightest UNSC veterans, and then transformed using safe and effective medical procedures to become stronger, faster and tougher than any normal soldier. New manufacturing methods and scientific advances also made mass-production of Mjolnir armor possible. The combination of new augmentation protocols and next-generation powered assault armor has proven to be a defining capability for the UNSC in the post-war period.

Spartan Field Manual Pg 22