This is a really tough mission! It requires that you snipe MOST of the guys guarding the convoy AND the sniper running up and down the hill, get to the RPG and fire it BEFORE the APC unloads all extra guards! Whew! Anyway, here's how you do it.
You have to finish the previous mission with the sniper rifle.
As the mission starts, run to your LEFT and lay down in a bush just on the hill about 100 feet away. Lay down and stick out of the bush just far enough so none of the branches block your view.
Now, there are 3 trucks with guards on either side of the trucks AND one guy down on the other side of the road AND a sniper running around.
Snipe the guy in front of the last truck (farthest to your left). This causes the guy on the other side of this truck to come to the front of the truck. Snipe him. Sometimes he doesn't run to the front and you'll have to pick him off later.
Then, sweep to your right and snipe the guy in front of the second truck. Immediately, sweep a bit farther to your right and snipe the guy standing on down below the other side of the road. You'll just see his head sticking up. Drill him! This causes a green-shirt guard to step out from behind the middle truck. Drill him. Now, get after the sniper. He's on the hill. Drill him while he stands looking around. You are going to leave two guys standing. One is the guy on the other side of the middle truck and the guy on the other side of the truck with the EMP chip inside.
Get up and toss your rifle! RUN down towards the back of the second truck straight for the RPG. Keep running straight for the truck! Then WALK the last bit up to the RPG and grab it. Step back around the truck to block the guard from seeing you. Aim and fire at the APC! If you miss then reload and fire again. I missed and reloaded and fired BEFORE the APC stopped and still finished in time. But, try not to miss the APC!
By now, you've taken out the APC so there are no more guards coming from that side of the convoy but you still have the two guards to deal with. Once you've taken out the APC then immediatelly toss the RPC. It's heavy and slows you down.
Crouch walk over to the back of the truck with the control panel and lay flat. Get out your silenced pistol and shoot the guard on the side of the middle truck in the back (or legs). Fire a couple quick shots and he drops.
Crouch and the control panel is right there. Unlock the control panel and the door of the truck opens. Crouch jump into the truck and crouchwalk over to the EMP chip. DON'T RUN TO THE EMP CHIP! Otherwise, the guard on the other side of the truck will run around to see who is inside that truck and start shooting. Once you've grabbed the EMP chip, crouch walk out the back of the truck and crouchwalk around to the front of that truck. The guard is facing away from you. Shoot the guard in the back of the head.
Get up and start running straight towards the machine gun nests! While you are running, toss your pistol and everything else you're carrying. Run up the back hill throught the woods and get to the landing area. Stand and wait for the rescue chopper to arrive. Mission Accomplished!
After doing this mission repeatedly in times of 4:30 and sometimes at 3:30, I was beginning to think that this mission couldn't be done in under 3:00 minutes. Once I was able to snipe the rest of the guys guarding the convoy WITHOUT worrying about the 2 other guys left standing, I was able to start completing this mission in under 3:00 but I kept being seen. The only thing I had to figure out after that was how to get to the RPG, fire it, and then kill those 2 guys left standing without having been seen. Don't worry about these two guys! You've got to get to that RPG before the APC unloads all the other guards. Stay focused on doing that! If you can kill the APC before it unloads the extra guards, you'll have plenty of time to kill the last 2 guys, get the chip, and make it to the exit point.
Lots of fast sniping! It'll take a bit of practice. But don't hesitate to immediately get up and toss the rifle and RUN! And, sometimes the APC fires at you while you are running but keep moving. Get to that RPG as fast as you! You MUST take out that APC!
I finished in 2:21 without being seen, 100% health, 100% accuracy.