Complete the Campaign on Hard
You will have to complete this game on "Hard" difficulty to unlock this achievement. The game shouldn't cause you too many problems at all, but there are a few pointers that will make it a little easier if you are struggling:
- Choose the right weapon for the situation - Change your weapon to suit your needs when possible
- Use the tactical binos to scan areas once you enter them while will show all enemy locations
- Use to have your teammates engage enemies, and reveal them on your map also
- Stay close to cover at all times and be ready to hide when necessary
- Take your shots while crouched and stationary, and avoid enemy grenades
- If stuck, try a different approach to the situation
With these few tips, you should be able to beat the campaign without too much difficulty. The achievement will unlock as soon as you complete Mission 7: Suez, and should stack with the Easy and Normal difficulty achievement. If those do not unlock, complete the final level on those difficulties while going for the other endings.
You can find a hard walkthrough on YouTube HERE.