Keep the gun aimed forward as you exit the base. Fire on the Road Block. As you exit the base, turn the turret behind your jeep. Destroy the jeeps that come into view. When your jeep falls into the ice, begin making holes in the ice to stall your pursuers. Keep firing into the ice to destroy the snowmobiles. When you exit the tunnel, you will be attacked by jeeps on the left and right sides. Destroy them quickly by blowing holes in the ice. If done correctly, you can prevent reinforcements from arriving. After crossing under the bridge, change your focus to the jeep's left side. After the right side jeeps are down, turn to the front of your vehicle. More jeeps will assault you from ahead. You will be in the clear when the sun comes out.