Full list of all 25 Halo: Spartan Assault (Windows) achievements worth 250 gamerscore.
The base game contains 20 achievements worth 200 Gamerscore, and there is 1 DLC pack containing 5 achievements worth 50 Gamerscore.
Earn all Gold stars
Complete 75 mission specific challenges
Complete Operation E, Mission 1 with the Hollow and Black Eye Skulls active
Earn 25000 XP throughout your career
Prevent all Jackals from regenerating their shields in Operation B, Mission 3
Finish the objective without using any vehicles/turrets in Operation E, Mission 4
Use every armor ability at least once (excluding Overshield and Seeker Drone)
Earn all medals in the game at least once
Finish the objectives using only the Brute Shot, melee and grenades in Operation D, Mission 1
Complete Operation E
Kill a convoy target with every stationary gun in Operation C, Mission 3
Complete Operation D
Score a kill with every handheld weapon (excluding Rocket Launcher and Spartan Laser)
Complete Operation C
Complete Operation B
Keep all Wolverines intact in Operation A, Mission 3
Complete any mission with the maximum number of Skulls active
Complete Operation A
Earn your first Gold star
Earn a star of any type
Earn all Gold stars in Operation F
Complete all Operation F mission challenges
Complete Operation F
Complete Operation F, Mission 4 with the Blind and Thunderstorm Skulls active
Destroy all Mega Turrets with the Grizzly tank in Operation F, Mission 2