The list of units
The Frigate is the first purely military naval unit. It can safely traverse any water, bombard into adjacent squares, and attack other naval vessels.
A coastal city needs both iron and saltpeter in its Strategic Resource box to build Frigates.
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.