Full list of all 25 Halo: Spartan Assault achievements worth 250 gamerscore. It takes around 15-20 hours to unlock all of the achievements in the base game.
The base game contains 20 achievements worth 200 Gamerscore, and there is 1 DLC pack containing 5 achievements worth 50 Gamerscore.
Complete 75 mission specific challenges
Earn all Gold stars
Earn 25000 XP throughout your career
Complete Operation E, Mission 1 with the Hollow and Black Eye Skulls active
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
Use every armor ability at least once (excluding Overshield and Seeker Drone)
Finish the objective without using any vehicles/turrets in Operation E, Mission 4
Complete Operation E
Kill a convoy target with every stationary gun in Operation C, Mission 3
Prevent all Jackals from regenerating their shields in Operation B, Mission 3
Complete Operation D
Score a kill with every handheld weapon (excluding Rocket Launcher and Spartan Laser)
Complete Operation C
Complete Operation B
Earn your first Gold star
Complete Operation A
Keep all Wolverines intact in Operation A, Mission 3
Earn a star of any type
Complete any mission with the maximum number of Skulls active
Earn all Gold stars in Operation F
Complete Operation F, Mission 4 with the Blind and Thunderstorm Skulls active
Complete all Operation F mission challenges
Destroy all Mega Turrets with the Grizzly tank in Operation F, Mission 2
Complete Operation F