This is the first in-depth study of the Royal Navy's vital, but largely ignored small craft. In the age of sail they were built in huge numbers and in far greater variety than the more regulated major warships, so they present a particular challenge to any historian attempting a coherent design history. However, for the first time this book charts the development of the ancillary types, variously described in the 17th century as sloops, ketches, brigantines, advice boats and even yachts, as they coalesce into the single 18th-century category of Sloop of War. In this era they were generally two-masted, although they set a bewildering variety of sail plans from them. The author traces their origins to open boats, like those carried by Basque whalers, shows how developments in Europe influenced English craft, and focuses in on the relationship between rigs, hull-form and the duties they were designed to undertake. Visual documentation is scanty, but this book draws together a unique collection of rare and unseen images, coupled with the author's own reconstructions in line drawings and watercolor sketches to provide the most convincing depictions of the appearance of these vessels. By tackling some of the most obscure questions about the early history of small-boat rigs, the book adds a dimension that will be of interest to historians of coastal sail and practical yachtsman, as well as warship enthusiasts.