Chapter 3-1

Ok I'm pretty new to this...so like give me a little break =)
Well when you start off in the mission kill the two guards on the balcony, either with a pistol, or grenade (best to save your rifle for later on) when they have been killed make your way round until it comes to a cut scene, and then wait till the cannon has fired before running to your left, where the two guards where before, be sure to have ashley still with you, when here you should get some ammo, when you have got this, go out and walk where you where before, but this time turn left, and there should be a bit of a bridge there, go slightly out so that the zombie in red cannot see you, then equip yourself with the rifle and aim for a red barrel, this blows all the enemies apart, then walk carfully upstairs and there should be another catapult on the right, take cover behind a wall, and make sure he can't see you to fire at you, then do the same as before and take out the red barrel..do the same for the rest of the catapults, and if you can't shoot the barrel, aim for the zombie shooting the fireballs.....when this is done, go to the end of the wall to bring up the cannon, and then fire at the door...when this is done, there will be a cut scene.. And then two or more zombies should come from the end of the wall, take them out and then go towards the door...
Also, make sure you have ashley with you at all times, I started off this mission by leaving her near the beginning, and she ended up getting took away, so it's best to keep her with you, to keep an eye on her..
This is how I done this mission so if it don't work I've probably explained it wrong lol

Here is what I did

You come to the crate with thge rifle ammo on it. Take it and shoot one of the guards with 1 shot. After that the second one should start coming down the steps wit for him and shoot or knife him. Then you go up the steps. A little cutscene will play. Wait for the catapults to stop firing and run up the next set of steps. When you get to the top wait for the next catapult to fire. After it does run towards the cabin on your right. Take out the guy in there. Go to the window and take out your rifle. Shoot the red barrel in front of you. Tell Ashley to stay in the cabin. Go out the door a little and shoot the red barrel on the right with your handgun. Go left bck where you came and there should be two dudes walking up the steps. Take them out and run back to the cabin. Go to that little tower in front of you and snipe the red barrel from the entrance. Look out the window with your rifle. There should be another catapult but no barrel. What you have to do is snipe the dude reloading the catapult. Then tell Ashley to come back. Outside the tower is a crank. Turn it and a cannon should pop out of the grond. Shoot it and it will destroy the big wooden door blocking your way.

Hope I helped!

I don't know what to do to make the cannon work, but I think you should stay at the botom of the stairs with Ashley, while shooting those gannados.

When you stat the mission go around the corner and snipe the ganodos walk up the steps and stop and make the catapults fire then run up the stairs on the corner and stop at the gate and snipe the red barrel. In 1 minute when you walk up the steps 2 monks will come for you their easy, when your done sniping the monks that you see go back by the stairs and snipe the monk in the little house he wears a metal mask so you can't do a grad shot carefully go in the house and take a yellow herb and a treasure before heading to the cannon which is across from the house you will see another caltupult but you can't see the red barrel so tell ashely to wait don't worrie no one will kidnapp her when the catupult fires and it hits make a dashing run to the little tower and snipe the monk raise the cannon and your done.