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.
Earn all Gold stars in all operation missions
Complete all campaign mission specific Assault Ops
Earn all co-op medals at least once
Earn all medals in the campaign at least once
Earn 25,000 XP throughout your career
Complete a co-op mission with at least 5 different players
Kill 10,000 enemies in co-op
Earn all Gold stars in all co-op missions
Complete all co-op missions
Use every ability in the campaign at least once
Score a kill with every handheld weapon in the campaign
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
Complete Operation E
Finish the objective without using any vehicles/turrets in Operation E, Mission 4
Complete Operation E, Mission 1 with the Hollow and Black Eye Skulls active
Complete Operation D
Finish the objectives using only the Brute Shot, melee and grenades in Operation D, Mission 1
Complete Operation C
Kill a convoy target with every stationary gun in Operation C, Mission 3
Complete Operation B
Earn your first Gold star in an operation mission
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