This achievement is typically the first achievement everyone will get.
You can get this achievement on any difficulty but Easy is the, well, easiest :)
During the first mission you will hear talk of stockpiled Stark weapons and you will be advised that is will be too dangerous to destroy them all. This statement could not be any more wrong. It is insanely easy thing to do!
Just watch out for yellow dots on your radar (on your HUD the weapons will also be highlighted in yellow). Make sure you destroy them all for this achievement. One missile (Y) will do the trick.