Book excerpt: Although previously undervalued for their strategic impact because they represented only a small percentage of total forces, the Union and Confederate navies were crucial to the outcome of the Civil War. In War on the Waters, James M. McPherson has crafted an enlightening, at times harrowing, and ultimately thrilling account of the war's naval campaigns and their military leaders. McPherson recounts how the Union navy's blockade of the Confederate coast, leaky as a sieve in the war's early months, became increasingly effective as it choked off vital imports and exports. Meanwhile, the Confederate navy, dwarfed by its giant adversary, demonstrated daring and military innovation. Commerce raiders sank Union ships and drove the American merchant marine from the high seas. Southern ironclads sent several Union warships to the bottom, naval mines sank many more, and the Confederates deployed the world's first submarine to sink an enemy vessel. But in the end, it was the Union navy that won some of the war's most important strategic victories--as an essential partner to the army on the ground at Fort Donelson, Vicksburg, Port Hudson, Mobile Bay, and Fort Fisher, and all by itself at Port Royal, Fort Henry, New Orleans, and Memphis.