Load up "World of Tomorrow" in Sapienza. Set your starting location to ICA Safehouse and smuggle a Jaeger 7 in the Safehouse as well. After you spawn and pick up the briefcase, (I would highly recommend carrying the briefcase instead of the sniper on your back) head down the stairs and to the left. Once you reach the water, head to the left-most dock. Push the two guys standing there off the edge. Retrieve your sniper rifle from the case and scope in on the larger sailboat sitting on the water. You'll have to shoot the bells on it in the order you see in the picture below.
You do not need to finish the mission for the achievement to unlock. The challenge however, you will need to finish the mission to get the XP credit for.