Advance
Naval Base
A whole section of the coast has been enclosed and specialized for the construction and maintenance of our grand fleet. This small city of sailors, craftsmen, and engineers is capable of building entire navies by itself, making it one of the most important strategic centers of our country.
Advance tree
The game files don’t say where this goes: it has no requires, so the game places it in the 
Revolutions tree itself.
Definitionin_game/common/advances/1_building_unlocks.txt:844
849ai_weight = {
850if = {
851limit = {
852has_ports = yes
}
854add = {
855value = 100
856multiply = num_of_ports
857divide = num_locations
}
}
}
862ai_preference_tags = {
exploration
}