Barry Finn has it pretty much right, privateers were sort of licensed pirates. There is a series of four novels by F. van Wyck Mason written in the early 1940s about the American Revolution. The protagonist in the first novel, who reappears in the middle volumes and then has a major role in the final tome, is an American privateer against the British. These novels, which I read in order in the '50s were first rate, well-researched and really gave the flavor of the period. Just as in real-life, the rebellionists won. Anyone interest in that period should try to find these books.