 By the later stages of the Eighty Years' War the Dutch had switched entirely from the heavier ships still used by the English and Spanish to the lighter frigates, carrying around 40 guns and weighing around 300 tons.The effectiveness of the Dutch frigates became most evident in the Battle of the Downs in 1639, encouraging most other navies, especially the English, to adopt similar designs.The fleets built by the Commonwealth of England in the 1650s generally consisted of ships described as "frigates", the largest of which were two-decker "great frigates" of the third rate.