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