Follow your leader and snipe/sneak into the facility. Once you regroup, use the Predator Missile and eliminate the enemies. Once you're done, you will enter the main facility and you have about two minutes to reach the sub. Use the Predator Missile on the Helicopter/tank and kill the enemies, rush to the right and get out at the fence. Kill the enemy near the garbage and use another predator missile at the vehicles. If you do this quickly enough, you get a check point. Use the predator missile to clear the enemies after this and run towards the sub. Once there, kill the enemies and climb the ladder with your team mates and use the predator missile at the enemy vehicles.