The Union Navy was the United States Navy (USN) during the American Civil War, when it fought the Confederate States Navy (CSN). The term is sometimes used carelessly to include vessels of war used on the rivers of the interior while they were under the control of the United States Army, also called the Union Army.
The primary missions of the Union Navy were:
- Maintain the blockade of Confederate ports by restraining all blockade runners; declared by President Lincoln on April 19, 1861 and continued until the end of the Rebellion
- Meet in combat the war vessels of the CSN
- Carry the war to places in the seceded states that were inaccessible to the Union Army, but could be reached by water
- Support the Army by providing both gunfire support and rapid transport and communications on the rivers of the interior.
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 Most were sailing vessels, some were hopelessly outdated, and one (USS Michigan) served on Lake Erie and could not be moved to the ocean.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.
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.
Because of haste in their design and construction, most of the vessels taken into the U.S. Navy in this period of rapid expansion incorporated flaws that would make them unsuitable for use in a permanent system of defense. Accordingly, at the end of the war, most of them were soon stricken from the service rather than being mothballed. The number of ships at sea fell back to its prewar level.