Guild Wars 2 – Operation: Bulwark

Head out to the Northeastern part of Martyr's Woods. You will find the entrance to the instance just a little to the Southwest of the Marytr's Waypoint.

Once inside just head over to the East. You will find your warband waiting for you there. It is time to give out assignments and take out the rear guard of the Flame Legion attack:

Hero: “Listen up! A Flame Legion Platoon is marching against the Black Citadel. Tribune Brimstone will engage the main enemy force while we take out the rear guard. Soure/Fyon, you're the mortar. Wait till we mark targets with green smoke, then light them up.
Soure Doomsday: “You got it, boss. Blowing stuff up at long range is my specialty.”
Fyron the Wraith: “Roger that. Why, I was putting mortars on targets when you were still gnawing marrowbones in the fahrar.”
Hero: “Elexus, you're our sniper. Pick a spot where you can cover the entire battlefield. We'll call your targets and you ventilate them.”
Elexus: “With pleasure. And if it takes me more than one shot per kill, you can shave the word 'loser' into my fur.”
Hero: “All right. We do this fast, we do this right, and everyone comes home in one piece. You get me? Now, move out!”

Elexus and Soure/Fyron move into position and then it is off into the battle. Head South and you will immediately encounter pair of Flame Legion Bladestorms. Focus in on them as they will be blocking the easiest ways to move around.

Mortar Signal: “Mark your target with a green smoke grenade, signaling your gunner to open fire with their mortar.”
Cooldown: 20s

Sniper Signal
Cooldown: 30s

Once they have been dealt with there are 3 Siege Weapons that need to be destroyed. The first is directly South of the 2 Bladestorms that you just defeated. Have your mortar target it to quickly destroy  the catapult. With that destroyed you just have to contend with the 4 Flame Legion soldiers who are around. They will take good damage from the mortar blast it will not kill them unless it was a direct it.

With the first siege weapon destroyed, continue on to the South. You will find a second Siege Weapon. If possible, you can have Elexus target and snipe of the Flame Legion Fire Shaman at this point. Otherwise he will roam a wide circle around where most of the battle will be. He has a guard of 2 Blademaster, a Stalker and an Axe Fiend.

With those dealt with then it is time to start over to the West. You will find another pair of Bladestorms blocking the way. Beyond them, before the siege weapon, you may encounter a Flame Legion Lava Shaman with his guard. Call out the target to Elexus for a quick kill on what would be an otherwise difficult battle. He has 4 guards: 2 Bladestorms, Stalker and Axe Fiend. Defeat them all and there will be nothing more to worry about here.

Once you have dealt with the siege weapons then it is time to worry about the Flame Legion Shamans. The third Shaman is a Flame Legion Smoke Shaman. He wanders the eastern side of the battlefield. Just look around for him with his 2 Bladestorms and Blademaster.

Elexus Shredskin: “All clear, boss. The Flame Legion's rear guard is officially out of commission.”
Hero: “Outstanding. This warband is tail-clear, soldiers. Fall in. We're heading back to the citadel for a hot meal.”
Elexus: “Best warband in the legion! Hoo-ah!”
Hero: “Damn straight. Never let anyone tell you different.”

Take your pick of your rewards, the Black Lion Key and then feel free to leave the instance,