The path to the first floodlight
The master guarding the harbor is the closest target form your starting point. Go right to the minefield (M4,1). There is one trip mine (that needs to be disarmed) and teller mines (you can avoid them but when you disarm them, they are added to your equipment).
When you get through the field, run to the other side of the road - in the wire fence (M4,2) there is a hole that allows you to get inside the base. Go through it and immediately go to the building in front of you - the building is empty.
Now wait for a right moment to run outside by using the door from the east side, when the enemy next to the other building is not looking in your direction (or simply throw a rock behind him). Instead of going up by using the ladder, go around the building from northern side - there, you will find the stairs. The first floodlight (M4,3), one of the elements of air defense, is on the roof. Be careful because destroying it will make a slight noise.
Find the documents
Go down as fast as you can and go to the nearest stone stairs behind the tracks, a few meters ahead. On the upper level you can find one or two soldiers. Then, enter the wooden building - you can find an opponent in the first room.
Go to the adjacent room - there, you can find the documents (M4,4). From them you can learn where you can find the harbor master (M4,5). If you were quick in completing the steps then the harbor master should be in one of the smaller warehouses. His guards are standing in front of the doors so you should be able to kill him without any problems.
Get rid of the harbor master
Use the second hallway in the wooden house to the said warehouse and kill the master. However, if he is not in the house, like in the picture above, you can set any trap next to the entrance (the best are S-mines or trip mines).