Advance
Corvettes
Corvettes are a class of small warships that are designed to escort friendly vessels and harass the enemy, relying on speed and maneuverability rather than massed firepower.
Advance tree
The game files don’t say where this goes: it has no requires, so the game places it in the 
Absolutism tree itself.
Modifiers
Definitionin_game/common/advances/4_choices_mil.txt:348
350icon = global_trade_routes_advance
351for = mil