Instructions
Earn the Ascetic Armor by killing three opponents at once with the sword in a ranked free-for-all playlist. The Commando helmet is unlocked by killing four opponents within four seconds of each other. The Flight Armor helmet is won by beating the campaign on the Heroic difficulty setting. The Combat and Assault Elite helmets are available by default.
Destroy a vehicle with three or more enemies riding it to get the Scout helmet. Play 10 games over Xbox Live and earn both the Spartan Graduate achievement and the O.D.S.T. helmet. Play and win over Xbox Live in ranked matches to earn the rank of Spartan Graduate to get the Mark V helmet. Finish the fight on the campaign under the "normal" difficulty to secure the E.V.A. helmet. The C.Q.B. Armor and Mark VI Armor helmets are available from the start.
Obtain a Gamerscore of 1,000 points in Halo 3 and receive the Security helmet. Locate all 13 hidden skulls littered in the campaign levels to gain the Hayabusa helmet. Continue finishing matches in the top three spots over Xbox Live, and earn 50 EXP points to receive the Spartan Officer rank and the Rogue helmet. Beat the campaign game under the brutal Legendary difficulty level to be worthy of the E.O.D. helmet. The most difficult helmet to earn is the Recon helmet. You must unlock all seven Vidmaster achievements, four from "Halo 3" and three from "Halo 3: ODST," to get Recon.