This is definitely the hardest level in the game, and is extremely difficult to beat without destroying the Shield Bunker (1). the best way to get to the Shield Bunker is on speeder bike, and it has tons of health. Therefore, spawn as a rebel vanguard at your rear CP (6). Jump on a speeder bike and drive straight through the center of the map. Look out for trees, stumps, rocks, and other debris that you could possibly run into, causing the speeder to explode (NOTE: running into enemy troopers will kill them not yourself, which is useful unless you plan to run over your own soldiers). You don't necessarily have to go at top speed through the forest like in the movie; just make your way north, making sure not to leave the map.
When you get there, don't assume that the enemy units don't know you're there; just drive right up to the entrance to the bunker and get off the speeder bike. Note: you CANNOT drive the bike into the bunker. As soon as you dismount, run inside to get away from the turret fire. (If you want, you can place mines down the hallway.) Stand between the health droid and the side wall and fire all ten of your rockets at the console right next to the command post hologram (the keyboard below the screen), NOT the long reactor core (while unconfirmed, there is a rumor that firing into the reactor does just as much damage) the damage of the bunker will be indicated below your own health in red. Once all your rockets are gone, switch to your pistol (for protection) and unload all your grenades (try to do it so that the grenades hit the wall then bounce back onto the CP otherwise the explosion may kill you).
That was the easy part - now you need more ammo to finish off the shield generator. Walk back up the hallway and take down anybody who gets in a turret, being sure to only expose yourself to one turret at a time by hiding behind opposite sides of the entrance once they begin to fire. It'll take about three units for each turret, and they will stop respawning here for a short period of time. Run out of the tunnel and turn left, there will be an ammo droid near the turret (assuming you haven't destroyed it). Get 6 rockets (more if you have time) and go back into the bunker. Once you destroy the Shield Generator, you can do anything you want - their reinforcements drain quickly enough that no more work is required in order for you to win this battle and the Galactic Civil War!