This really isnt a guide or solution, but rather a helpful warning. If you plan on going after this achievement, in order to get this you must start a new game, and start from level one, to ten. I found out the hard way by completing each level individually (i.e. I went to select mission and did it that way). Doing that will get you the level achievements, but not the Shell Shocked achievement.
Just a friendly warning. Start a new game, dont do each mission individually.