The following units can be upgraded to Frigates:
The Frigate is the most powerful wooden ship in the game. It can sink enemy shipping and bombard enemy city fortifications.
The frigate was a fast and powerful warship that evolved to fill several important roles, but one of its primary roles was to raid enemy shipping. These three masted ships were lighter and faster than the European great ship or man-of-war, and usually carried 36 or fewer guns. The frigate was powerful enough to overcome most of its prospective opponents and fast enough to escape those it could not outgun. Because of their speed and strength, frigates were often employed as escorts for merchant vessels during times of war. The frigate remained the most useful and dominant naval vessel until the development of the ironclad.