Key points of World Map - Forts - Assassin's Creed IV: Black Flag
In the Caribbean, there are 11 forts, which have been divided into three categories, depending on their difficulty level. In the upper part of the map, you can find easy forts: Dry Tortuga, Gibra, Eleuthera. In the middle of the map, there are the medium forts: Conttoyor, Castillo de Jagua, Cruz, Punta Guarico, Navassa. The forts of high difficulty level: Charlotte, Serranilla, Chinchorro, are at the bottom of the map. You can attack all of the forts with the moment in which you obtain the Jackdaw, with the exception of Punta Guarico, which will be unlocked in the main campaign mode, in sequence 5, mission 1.
A fort's difficulty level determines the speed with which the cannons are reloaded and the endurance of the fortifications. It does not translate into the numbers of the fort's crew.