From Halopedia, the Halo wiki
Not a Scratch
Not a Scratch is an achievement in Halo: Spartan Strike. It is unlocked by keeping the Type-26 Wraith 100% intact in Operation B, Mission 4. The achievement is worth 5 Gamerpoints. It is represented by a circle with an aerial view of a Wraith inside it.
Although the level is most easily completed in the Wraith, it is by no means necessary to do so. By killing all of the level's enemies on foot, the player can ensure the Wraith remains undamaged.