This achievement isn't too hard, even on Supersoldier difficulty. This achievement can be easily done during Mission 1 or 4, or throughout many other parts of the game. You'll just want to use your cloak to sneak up close to or behind an enemy, that is alone. Now, just pick up any object near them using , and throw it at them using , killing them instantly, regardless of what the object is. If you threw the object while cloaked, you will automatically cloak after the enemy dies, and get 1 credit towards this achievements. It is ok if other enemies notice that the enemy died, as long as they don't see your exact location and begin to shoot. Just continue to hide behind some cover, then cloak and stealthily kill enemies using any throwing object.