When you start the mission you must take down a guard on a sniping post. Crouch or walk quietly to sneak to him. When you are close, attack him with your knife. You must now shoot some guards before you regroup with your units. Shoot only when you hear thunder. You can predict when it happens by noticing the lightning. Take out the one on the left pier first when thunder strikes. Then, aim to the right where you can see two other guards on two piers. The thunder will strike, and you can take them both out quickly. You can also wait for thunder to strike again and take them out individually. Reload, then aim up slightly. A person will come down the stairs. Hit him when thunder strikes. You must now take out two guards at the same time with a one shot kill when thunder strikes. This can be difficult because the alarm is sounded when gunshots are heard.