 In the 18th century, the small and fast frigate and sloop-of-war—too small to stand in the line of battle—evolved to convoy trade, scout for enemy ships and blockade enemy coasts.Fast schooners and brigantines, called Baltimore clippers, were used for blockade running and as privateers in the early 1800s.These evolved into three-masted, usually ship-rigged sailing vessels, optimized for speed with fine lines that lessened their cargo capacity.