When you receive your weapons at the beginning of the game, wait until they reappear on the table. Keep gathering them until you have the max ammo capacity. Finish the training. After the airstrike training, your base will be attacked. Fight your way to the Humvee. If you run out of ammo completely for any weapon, go back to the Weapons Training table and get more. Climbing into the Humvee will start the next level.
In the next level, you will man a machine gun on the Humvee. It has unlimited ammo and does not have to be reloaded. If you are confronted by a large group of enemies, shoot nearby crates or barrels. This will release salt acid, instantly killing enemies near it. You cannot move on until all the enemies in the area are defeated. Later in the level, you get off the Humvee and join other Marines. You are confronted by terrorist on machine gun. You can shoot him, but men will keep coming to man it. You have to go through a pathway to the left of you. This will take you around the machine gun. Fight your way through until you reach the sniper. Go in front of his sight, he will kill you. Smoke grenades won't work here. You have to enter the building to the left. There are three or four men on the second floor. One of them pops out as you approach the balcony. Kill him, and approach the balcony very slowly. The open window to the left is where the sniper is. Carefully aim a frag grenade and throw it in the window. If you here him scream during the explosion, it was a good throw. Be careful not to go to near the broken part of the balcony or he will kill you. Once he is dead, you can jump off the balcony. Follow the objectives to complete the level. Try to pick up an AK-47 in place of the pistol. You can pick up 300 max ammo for it.