Play the game in single player on Normal or Hardcore difficulty. This Achievement will unlock upon completion of the fifth mission, "The Mountain King".
Note that the mission is in two parts, so when it first appears that the mission is complete, you're actually just loading into the second half.
This level can be beaten fairly easily through running and gunning. Watch for the odd tank when you're running through on foot, and beware of rocket-launcher-wielding infantry in the towers. Even if they miss you, you could take some serious splash damage in those close quarters. Be sure to use the drones when you find them.