At the start of the American Civil War, neither side had warships on the Mississippi River, which was a vital strategic artery. In what would prove the vital naval campaign of the war, both sides fought for control of the river. While the Confederates relied on field fortifications and small gunboats, the Union built a series of revolutionary river ironclads. First commissioned in January 1862, these ironclads spent the next two years wresting control of the Mississippi, fighting in a string of decisive engagements that altered the entire course of the war. This book explains how these vessels worked, how they were constructed, how they were manned and how they were fought.