For most of the seventeenth century the Netherlands constituted the most important maritime power in the world, with by far the largest merchant fleet and a dominance in seaborne trade that other countries feared and envied. Born out of an 80-year struggle against Spain for independence, the Dutch republic relied on naval power to guarantee its freedom, promote its trade and defend its overseas colonies. The Dutch navy was crucial to its survival and success, yet the ships that made up its fleets are among the least studied of any in the age of sail. The reasons for this include a decentralised administration of five separate admiralties, often producing ships of the same name at the same time, the widespread co-opting of merchantmen into naval fleets, and competing systems of measuring ships, all of which leads to confusion and error.