 During the course of the war, the number in commission was increased by more than a factor 15, so that at the end the U.S. Navy had 671 vessels.Even more significant than the increase in raw numbers was the variety of ship types that were represented, some of forms that had not been seen previously in naval war anywhere.The nature of the conflict, much of which took place in the interior of the continent or in rather shallow harbors along the coast, meant that vessels designed for use on the open seas were less useful than more specialized ships.