1 - starting area
2 - destination (main gate)
3 - enemy outpost
Go back to your armored vehicle and start moving west. Eliminate everything that stands in your way. The good news here is that you're travelling alone, so you won't have to worry about O'Neill anymore. Leave the asphalt road once you've reached a new junction (screen).
Be careful, because you're going to get attacked by an enemy gunship in a short while. Remain inside your vehicle and use the turret to destroy the helicopter (screen). You may continue moving forward. Turn right at the next junction, because you shouldn't go back to the asphalt road just yet.
Eventually you should be able to find a small waterfall (screen). If your vehicle is badly damaged, consider leaving it and heading towards the water. Otherwise turn left and secure an enemy outpost. Start off by eliminating a Korean sniper. Once he's gone, deal with the remaining hostile units. Most of the soldiers are hiding near sandbags and that's where you'll have to look for them.
You may continue moving towards your current destination. This means you can go back to the main road. You should receive a new assignment once you're close enough to the harbour, however remain inside your vehicle for a few more seconds. Take your time to disable machine gun posts. Also, notice that an allied VTOL has appeared in the area and it will help you in distracting enemy soldiers.