Here is the full list of all 12 Congo Merc achievements.
Successfully finished your first mission.
Successfully finished the Campaign mode.
You saved your first civilians.
You saved 5 civilians.
You came across the aftermath of a massacre.
Eliminated the Rebel leader.
Killed 40 rebels.
Obtained your first piece of intelligence.
You failed to accomplish the mission.
Revealed 15 hidden objectives with reconnaissance.
Transported a unit or a force by airplane.
Transported a unit or a force by water.