[5] To accomplish its wartime missions, the Union Navy had to undergo a profound technical and institutional transformation.

During the war, sailing vessels were completely supplanted by ships propelled by steam for combat purposes.

Establishing the ranks of admirals also implied a change of naval doctrine, from one favoring single-ship operations to that of employing whole fleets.

Before the war, the United States Navy emphasized single-ship operations, but the nature of the conflict soon made whole fleets necessary.

Most were sailing vessels, some were hopelessly outdated, and one (USS Michigan) served on Lake Erie and could not be moved to the ocean.

[10] The variety of ship types represented was even more significant than the increase in raw numbers, some of the forms not previously seen in naval war.

The nature of the conflict, much of which occurred in the continent's interior or shallow harbors along the coast, meant that vessels designed for use on the open seas were less useful than more specialized ships.

[14] 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.

[16] 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 defense system.

The number of hands in the Union Navy grew five times its original strength at the war's outbreak.

Most of these volunteers were rated as "Land's Men" by recruiters meaning they had little or no experience at sea in their civilian lives.

However, many sailors from the United States pre-war merchant marine joined the navy, and they were often given higher ratings due to their background and experience.

The sailors were typically unemployed, working-class men from urban areas, including recent immigrants.

They seldom enlisted to preserve the Union, end slavery, or display their courage; instead, many were coerced into joining.

[27] Thus unlike the army, the Union navy did not prohibit African Americans from serving at the start of the war and was racially integrated.

Bennett argues: The blockade of all ports in the seceded states was proclaimed by President Abraham Lincoln on April 19, 1861, one of the first acts of his administration following the bombardment of Fort Sumter.

Finally, it cast doubt on the ability of the Confederacy to defend itself, thus giving European nations reason not to grant diplomatic recognition.

The final important naval action of the war was the second assault on Fort Fisher at the mouth of the Cape Fear River in North Carolina.