When you go down the stairs in the Final Countdown you will see a man at a machine, kill him and 2 more men will appear, kill them as well.
After that make sure that your health is full, you've got four grenades and your weapon ammo is full.
Then go to the middle of the bridge.
Now find somewhere to cover (the forklift will do just fine) and wait untill he shoots down a red box, then when he's about 2 seconds away from it shoot it untill it explodes.
if you run out of bullets just use your grenades and if you run out of them you'll notice a hammer and a spanner just time it right and lob it at his head.