Here is the full list of all 35 Crossfire: Sierra Squad achievements.
Clear the Story Campaign in Arcade mode.
Defeat 10 named enemies.
Defeat 10 minigun heavy armor units.
Defeat 5 heavy armor units.
Defeat your first launcher heavy armor unit.
Eliminate your first LAV.
Defeat your first heavy armor unit.
Defeat your first minigun heavy armor unit.
Eliminate your first Boss.
Use a grenade in a mission.
Get downed for the first time.
Cleared your first mission.
Use a stimpack in a mission.
Purchase your first weapon.
Equip a weapon for the first time.
Purchase your first modified part.
Equip your first modified part.
Equip a weapon found on the battlefield.
Purchase a Sub-Machine Gun.
Purchase a pistol.
Purchase a DMR.
Destroy your first helicopter.
Equip your first perk.
Play your first Horde Mode run.
Purchase 10 weapons.
Purchase 15 weapon parts.
Defeat 3 launcher heavy armor units.
Destroy 10 helicopters.
Destroy 5 LAVs.
Upgrade a weapon to Rank 2.
Upgrade a weapon to Rank 3.
Obtain both perks for a weapon.
Clear all Squad Missions.
Clear the Story Campaign in Realism mode.
Clear Stage 10 in Horde mode.