This achievement is easy as long as you play patiently.
- Always use green (full) cover when possible, even if it means fighting at medium range.
- Don't get out of cover unless there are no more enemies in range of your Shock Troops.
- Flank the MG on the right side, keeping in green cover.
- Use grenades liberally on groups of enemies. You won't run out of munitions that easily.
- Ignore the civilian rescue side mission, unless you are confident you won't lose men.
- Pick up any LMGs you can find laying around, they increase your medium-long range firepower.