Capturing Cabo de Cruz is the only fort needed to get 100% synchronization of the main memories, outside of the one automatically captured in the story section of the game. Cabo also has a habit of being surrounded by ships in the Restricted Zone, so approach it from the west where the least amount of ships are located. As soon as you are within the 500m range for Mortar fire you should barrage the fort, weakening the nearest defenses so that when you are within cannon range you can finish them off quickly.
Once you are on the ground, enter the fort through the lift and the wall to the left of the main gate. Straight ahead is the first Captain, which you can shoot with a Berserk Dart, and then climb the wall to the left to sneak up behind the other Captain and air assassinate him. Wait for the first Captain to die, if he hasn't already, and then 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, Driftwood.
