John Newland Maffitt (American National Biography)
Like other Confederate high seas raiders, John Newland Maffitt both embarrassed and damaged the northern war effort. His destruction of Union shipping removed tonnage from service and at the same time forced Union ship owners to pay ever higher insurance premiums. His success, and that of other Confederate high seas raiders, forced the Union navy to divert much needed resources away from the blockade to the task of chasing these will-o'-the-wispish sea rovers.
William M. Fowler, "Maffitt, John Newland," American National Biography Online, February 2000, http://www.anb.org/articles/05/05-00463.html.