EVA: Complete Campaign on Normal, Heroic, or Legendary
EOD: Complete Campaign on Legendary
Security: Earn 1000 out of 1000 Gamerscore Points for Halo 3
Scout: Complete "Used Car Salesman" Achievement
Mark V: Complete "UNSC Spartan" Achievement
ODST: Complete "Spartan Graduate" Achievement
Rogue: Complete "Spartan Officer" Achievement
Hayabusa: Collect all skulls
heres how to get the rest of the armor