In the Military base level, you must shoot down a helicopter to gain intel on the rocket facility that belongs to the general. It can be difficult to shoot it down. After you destroy the train, you will go through a series of corridors. In the one that leads to the heli pad, a man runs out the door to warn the general and pilot that you are coming. Do not shoot him. Note: Enable the "God mode" code or he may kill you. Save the game in case the chopper does get away. After the man runs out, do not move out the door or the helicopter will lift off. Then, aim for the pilots window and empty a clip at the pilot. He should die, but just in case, run out and keep firing at the pilot. A glitch will happen; the helicopter will take off after he dies, but it will then crash. Make sure to empty at least a magazine or more to break the window and another to kill the pilot. Do not kill the general.