1. Power down communications dish: easy, medium, hard 
2. Obtain safe key: medium, hard 
3. Steal building plans: medium, hard 
4. Enter base via ventilation tower: easy, medium, hard 

Unlike the easy mission, fewer soldiers chase you, but they're better at aiming their weapons. Follow the road to a crossing that splits to a small house on the left and right. Two guards shoot at you on the right. Kill them and grab the booty inside. Skip the left house for now. 

Continue on down the road, keeping the big satellite dish in sight. You have to power it down anyway, so use it to guide you when disoriented. Along your path is an observation tower, which has nothing in it. Skip it. When you're at the satellite dish, take a right. Along the way, you should pick up the Klobb, a fast-shooting, automatic machine gun. It's excellent, albeit loud. A small guard construct and two houses appear. Ignore the metal girded construct and the first house and head to the other slightly farther house, the one at the end of the road. You'll find the hut door key, grenade launcher, and more grenade ammo. A beige-suite military official has the key. Kill him off. 

Now, remember that hut at the beginning of your journey we told you to skip? The military officer you just killed gave you the key to it. Run back to that first hut, ignoring soldiers. Just run and occasionally strafe to avoid gunfire. Unlock the hut door, grab the safe key. Objective B completed. Now head back to the main road, and be sure to reload because they will be some a few out-of-breathe guys wanting to kill you. 

Head straight to the main satellite, ignoring any distractions. Enter the facility and run up the stairs. In easy mode, you simply walk in and open the door, ascend the stairs to the door, and press B to power down the satellite. In medium and hard you have to unlock it with the key, and power it down. Just don't shoot the computer, which will sound the alarm. Run down the stairs. 

Two more objectives to go (in medium and hard). You must obtain the map, in the very dangerous bunker compound, and find the ventilation shaft. Turn left once you leave the satellite area. Follow the path to the compound. There are many houses; enter the first house on the left to unlock the safe, grab the map, and head out. If you want to get rid of some guys, use your grenade launcher, aiming at the barrels. That'll get them for sure. Still, the best idea is to run, because there are too many guys around. 

Where was that ventilation shaft again? If you're at the enemy bunker where you found the map, with the gate to your back, look to your right. There is a narrow road to the left of the satellite dish (off the main road) that leads to the shaft. Pass the satellite, follow the path, and then stay to your left. You'll see in about four seconds. Climb up to the top of the shaft, pull out your silenced PP7, and then blow off the four locks with two shots per lock. The grate will drop out of sight, and then you're home free.