This achievement can be done at the start of the game. After all of the cut scenes you will wake up in a German u-boat in a wheel chair at first you won't be able to take down anyone but as soon as you talk to the second person their will be an enemy on the left who you can get behind and stealth take down using
as soon as he goes down your achievement will pop.
If you would like to see a video about what I am talking about, I will leave mine below.