REWARDS - Money from Russian dealer
Hop in a car and take a long drive to the yellow blip on the radar. When you arrive, you'll notice a lot of security located around the warehouse. You'll have to approach this situation very carefully, since there are a lot of men and two forklifts carrying explosives outside. Take out the two forklifts outside by using the ledges to gain a height advantage, then take out the men too before heading inside. To get inside, you'll have to shoot the keypad on the wall.
Once the door opens, you'll be greeted by a few men, so take your time and kill them. If you need armor, there's a pickup on the outside, just to the right of the door. Strafe (target without locking onto anyone) through the next area and listen closely to any gunfire. Once you get to the big open area, shoot the guy on the balcony and the two guys to the right. Once you're sure you've killed everyone, head upstairs and into the office.
Your ultimate goal here is to kill the Russian arms dealer, represented by the red blip on your radar. He is tougher than the normal goons, so quickly dispatch of any normal guys and give chase to the Russian. If you don't kill him quickly enough, he'll get in a car and start driving away. If that happens, get on the bike nearby (pick up the weapon) and pursue him. Make sure he's in front of you and shoot at him that way. It is a lot easier to shoot him frontways than a normal drive-by, since he drives pretty fast. You cannot let him get away, or you'll fail the mission. Once he's dead, you'll pass the mission.