<P> To accomplish these, the Union Navy had to undergo a profound transformation, both technical and institutional . During the war, sailing vessels were completely supplanted by ships propelled by steam for purposes of combat . Vessels of widely differing character were built from the keel up in response to peculiar problems they would encounter . Wooden hulls were at first protected by armor plating, and soon were replaced by iron or steel throughout . Guns were reduced in number, but increased in size and range; the reduction in number was partially compensated by mounting the guns in rotating turrets or by pivoting the gun on a curved deck tracks so they could be turned to fire in any direction . </P> <P> The institutional changes that were introduced during the war were equally significant . The Bureau of Steam Engineering was added to the bureau system, testimony to the U.S. Navy's conversion from sail to steam . Most important from the standpoint of Army - Navy cooperation in joint operations, the set of officer ranks was redefined so that each rank in the U.S. Army had its equivalent in the U.S. Navy . The establishment of the ranks of admirals implied also a change of naval doctrine, from one favoring single - ship operations to that of employing whole fleets . </P> <P> At the start of the war, the Union Navy had 42 ships in commission . Another 48 were laid up and listed as available for service as soon as crews could be assembled and trained, but few were appropriate for the task at hand . Most were sailing vessels, some were hopelessly outdated, and one (USS Michigan) served on Lake Erie and could not be moved to the ocean . 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 . </P> <P> 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 . To confront the forms of combat that came about, the federal government developed a new type of warship, the monitor, based on the original, USS Monitor . The U.S. Navy took over a class of armored river gunboats created for the U.S. Army, but designed by naval personnel, the Eads gunboats . So - called double - enders were produced to maneuver in the confined waters of the rivers and harbors . The Union Navy experimented with submarines before the Confederacy produced its famed CSS Hunley; the result, USS Alligator failed primarily because of lack of suitable targets . Building on Confederate designs, the Union Navy produced and used torpedo boats, small vessels that mounted spar torpedoes and were forerunners of both the modern torpedo and destroyer type of warship . </P>

How many ships did the union have in the civil war