Their were a type of many riverboats, lightly armored, and used throughout the Mississippi River system. They were armed with 32pdr smooth bores, and armored with .25 to .5 inch sheetmetal. They were called "Tinclads" by the brownwater Union navy.
The "Tinclads" were used extensively throughout the war and managed to keep the Confederates navy from using the rivers most of the time.