Free the captives undetected
Find and kill the general
Perform stealth assassinations from a corner spot 0/3
Head on forward with the rest of Haytham's men. When the officer shows an interest in your group, give the order to take him down.
After that, if you want to take down the General, break off to the right. Sneak along the back of the tents that are in the area to the stocks in the back of the area. Move unto the bushes and wait by the crates for the General to move in. When he is in range, strike him down. Now sneak back to the main rock back along the same path. Head to the entrance of the fort where your men are waiting.
Once there, before going inside the fort, go over to the left. Move between the wall and the tents to make for the first set of captives. Move into the bushes nearby them and wait for the Officer to come nearby. If you want to get 1 of the Corner assassinations out of the way, then move against his tent while he is inside it. When the officer comes out you can easily get him with a corner assassination. After you take him out, then free the nearby captives.
Time to move onto the next group of Captives. Turn to the North and sneak to the second group. Move into the bushes just before them and wait. There is an Officer, like last time, patrolling the area. With careful timing you can get another corner assassination. Just wait for the Officer to head around the bushes toward the tents. Move to the corner of the crates nearby him. Take him out as he comes to the crates. After that quickly free the captives. After that it is time for you to deal with the final group.
The final group is not far away. Head down to between the crates and the shore. Advance along the dock to the crates at the start of the junction leading out toward the ship. Wait for the Officer to get down toward the end of the dock and dart over to the second set of crates nearby the ship. Take a lean at the corner of the crates and wait for him to come back toward you. Kill him with a corner assassination to finish the optional objectives. Climb up onto the ship and head for its stern. There is 1 Officer in the area for you to deal with and at least 3 Soldiers. Try to kill the Officer so he falls into the water. At least 1 Soldier will come to investigate so clear out quickly after you take him down. Wait for the soldier to move back to his position by the captives on the boat. Assassinate him then free the captives.
Inside the fort:
Kenway: See? I'm freeing you just as I said I would. Now if you'll allow me to explain-
Kenway: Let her go.
Hickey: But she'll give us away.
Kenway: No she won't.
Pitcairn: What's the plan?
Kenway: Free the captives and avoid detection.
Church: What of Silas?
Kenway: He dies.
Pitcairn: Signal when you're ready to strike.