Full list of all 28 Halo: Spartan Assault achievements worth 400 gamerscore. It takes around 20-25 hours to unlock all of the achievements on Xbox 360.
Complete Operation E, Mission 1 with the Hollow and Black Eye Skulls active
Complete Operation E
Finish the objective without using any vehicles/turrets in Operation E, Mission 4
Finish the objectives using only the Brute Shot, melee and grenades in Operation D, Mission 1
Kill a convoy target with every stationary gun in Operation C, Mission 3
Earn 25,000 XP throughout your career
Use every ability in the campaign at least once
Earn all medals in the campaign at least once
Score a kill with every handheld weapon in the campaign
Earn all co-op medals at least once
Complete all co-op missions
Earn all Gold stars in all co-op missions
Complete a co-op mission with at least 5 different players
Complete Operation D
Complete Operation C
Complete Operation B
Finish the mission without any Jackal regenerating its shield in Operation B, Mission 3
Complete Operation A
Keep all Wolverines intact in Operation A, Mission 3
Complete any campaign mission with the maximum number of Skulls active
Earn a star of any type in an operation mission
Earn your first Gold star in an operation mission
Earn all Gold stars in all operation missions
Complete all campaign mission specific Assault Ops
Complete Operation F
Destroy all Mega Turrets with the Grizzly tank in Operation F, Mission 2
Complete Operation F, Mission 4 with the Blind and Thunderstorm Skulls active
Kill 10,000 enemies in co-op