Spartan Officer
From Halopedia, the Halo wiki
Spartan Officer
Spartan Officer is a Halo 3 multiplayer achievement. It is earned when the player gains 50 experience points in a certain playlist and a rank of at least 
Lieutenant on Xbox LIVE. It is represented by a gold plate with an eagle holding three black arrows and a black thunderbolt, with three pips behind it.
Following the shutdown of Xbox 360 Halo online services in December 2021, this achievement will no longer be attainable.[1]
Rewards
Unlocking this achievement rewards the player with the following;
- 25
- Rogue multiplayer armor permutation for player use.
Glitches
- It is said by many players that they got the achievement at the same time as the Vidmaster Challenge: Lightswitch Achievement, and it didn't go through. Others did not get the achievement when advancing to a Highest Skill of 10, skipping last
Gunnery Sergeant ranks and going straight to 
Lieutenant. - If a player has obtained the Spartan Officer Badge but didn't get the achievement, they can still obtain the achievement by getting a lieutenant rank in any of the new playlist-specific ranking systems.
Gallery
Spartan Officer Medal.
The Rogue helmet.
Sources
