This is probably the easiest level in the game, takes at most 5 minutes. Here are 3 easy steps to beating this level. I will not worry about spoilers because this game has been out forever!
1) Basically in the beginning all you have to do is kill the enemies that approach in trucks. If you find it too difficult to stay alive while standing up and shooting them, try and go prone and shoot the enemies through the wood on the side of the truck, you will be able to kill them but they will not hit you. Make sure to take out all the RPG enemies as they can kill you in one shot (Whenever you hear "Lookout, RPG" just start killing the guys in the truck as fast as you can)
2) After taking out a couple truck loads of enemies, a new challenge approaches, a helicopter. Try your best to kill it with the RPG supplied to you on the wooden crate, but it is very hard. After a while the helicopter will leave you alone and go ahead and blow up the bridge you are on.
3) Now is one of the easiest parts. Many enemies will approach you from trucks, from the ground, and out of helicopters. You can try to kill as many as you want but sometimes if you get hit even twice, you are dead. What I found to be the easiest was to go prone behind the lower level of the bridge for protection. Your allies will wipe out the bad guys, taking you to the final part of the mission. 3 bad guys will approach, all your allies will get killed, and you will now have a pistol. Simply shoot and kill all 3 bad guys and.... DONE!
Hope this helps!