Gibara is best approached from the west or the north, as the east usually has frigate infested water that can pose a serious issue. While the fort is weak at only 3 defenses, the main gate has Heavy Shot cannons that can eat into the Jackdaw's health if you stay in range too long. It is best to sweep across the area quickly and aim at the gate from an angle, rather than straight on to quickly take out the threat and then deal with whatever is left over.
Once you are on the ground, Gibara has the same layout as Fort Eleuthera. As with Eleuthera, enter by climbing the wall to the left of the main gate and follow the rampart to the far side. You can then head south up the stairs and climb up the scaffolding on the nearby building to reach the upper level where you'll spot the Captain below on the other side for an easy air assassination. You can then climb back up and enter the war room and kill the fort's Commander.
After the fort is cleared you can get the Treasure x2, Animus Fragment x2, and start the Naval Contract, Silk on the Waves.
