Spartan Officer
From Halopedia, the Halo wiki
Spartan Officer
Spartan Officer is a Halo 3 Multiplayer Achievement. It is earned when the player advances to the rank of Lieutenant, Grade 1 (Gain 70 experience and a skill level of at least 10) on Xbox Live. This Achievement gives 25 Gamerpoints to the player.
It is represented by a gold plate with an eagle holding 3 black arrows and a black thunderbolt.
It unlocks the Rogue Helmet for multiplayer use.
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Unfortunately this is not all true, for some reason some ppl dont get the achievement such as myself. I am a spartan CAPTAIN and i still do not have the achievement in fact it is my last one...