Co-Op - Drop 'em Like Liquid

Drop 'em Like Liquid - Co-Op

Bonus: Reach and save the hostages without alerting any enemies to unlock the "Bullseye" achievement

Again, recommended on easy difficulty and preferably with a friend. Having headsets is critical for communicating and timing your shots. You must take out the guards with one shot, so having individual targets and countdowns for synchronized shots is vital for this achievement.

Go down the sewer and follow the tunnel until you spot the first enemy. Take him out, then climb up the ladder to ground level. Once there, you and your buddy must take coordinated, synchronized shots to ensure the pairs of guards are taken out at the same time. Drop the first two by the yard then the next two inside the aparment entrance ahead.

Continue upstairs then wait for the prompt to open the door with the ammo crate inside. There are two enemies inside that you must kill quickly. Fortunately, these are not counted towards the "not to alert" enemy list so don't be vexed. Next, loo to the window to locate Alpha Team. Zoom in and two guards will walk by. Do not shoot them immediately as they come into view (when the leftmost guy is still on the stairs). Wait for them to walk a bit more to the right and be completely still before taking your shot.

Next, the next pair of targets will be marked and they will position themselves behind a van. Again, wait for them to stand still before taking them out. Next, you'll have to take out the guards with hostages inside the two buses in the plaza. You and your buddy must pick one bus each. Kill the guards as soon as Alpha team deploys their flashbangs.

Replenish your ammo then head out to the streets. Two pairs of guards will be marked so take them out with synchronized shots as well. Now, one of you must stay in his current position while the other jumps down to the walkway below. There will be three enemies in the next set of targets. The team mate who stayed in position can pick off one easily but the team mate who took the walkway must take down two enemies with one bullet as they line up. If you mess up, just jump in the water to commit suicide and load the last checkpoint.

Go back to street level then look towards the hotel. Three enemies will appear so take out the the left and right guards first before taking out the one in the middle. Next, run to the right side to get a clear view of the set of enemies walking from the right side. Take them out as fast as you can. Next, locate the middle set of enemies. You must take them out as quickly as you can since they're in the process of calling in reinforcements. (therefore messing up your achievement operation). Move to the left side again, to get a clear view of the windows of the building ahead, then take out the sniper.

After the mission updates, head to the next vantage point. Once the target pair of guards appear, take them out with synchronized shots. Wait a bit and two more targets will walk in from the right side of the embassy grounds. Take them out as well. Next, three more enemies will appear in the middle, by the fountain. Kill them as quickly as possible.

Next, wait for Alpha team to stack in by the window and wait for the targets to stand still. Don't hesitate to fire multiple rounds because the distance and other obstacles won't always guarantee a one-hit kill. Wait for Alpha team to move upstairs and stand by the windows. Wait for the four targets to appear then order Alpha team to deploy the flash bangs. You and your buddy must take out two targets each as fast as you can. The achievement should pop up after this sequence.

Thanks to TheGamerReview for the very helpful pointers.