Once the Union Army gained control of the upper rivers of the Mississippi Valley during the first half of 1862, slow and heavy ironclads proved ineffective in patrolling the waters. Hastily outfitted steamboats were covered with thin armor and pressed into duty. These "tinclads" fought Confederate forces attacking from the riverbanks, provided convoy for merchant steamers, enforced revenue measures, and offered tow, dispatch, and other fleet support services. This history documents the service records and duties of these little-known vessels of the Union fleet.