Perform 10 silent kills using a silenced handgun
Can be achieved in any sense where the hand gun is a weapon selection option, ensure silencer is equipped.
Difficulty preferably on the easiest and head shots as standard required to ensure things don't get messy, also securing the 'silent' bit.
What I did in the end was to Load up the first level, try not to fall asleep as you press X to escape all the scenes, swim jump kill kill kill some until you reach a certain commander (signal caller) he is in possibly the second gun pillbox you see, the hand gun is on the desk, equip it - ensure the silencer is on and the very next cluster of enemies are your meat, go and whip some heads, restart checkpoint, rinse, repeat.
This was the first decent video that you tube spat out, feel free to find your own. This one is with credit to Chris Contagious
and his Destiny Trophy Guides
, be sure to like his shit and whatever. Where his video starts is just after where the gun is first available.
Took me two attempts.