USS Katahdin was a Unadilla-class gunboat built for the U.S. Navy during the American Civil War.
Contemporary sketch of USS Katahdin operating on the Mississippi River
The Unadilla class was a class of gunboat built for the Union Navy at the outbreak of the American Civil War. Ships of the class were also known as "90-day gunboats" due to their rapid construction. The class was designed to be fully oceangoing while having a light enough draft to be able to operate close inshore, for blockade duty or other operations in shallow waters.
Lithograph of a Unadilla-class gunboat, ca. 1861
The hulls of the Unadilla-class gunboats may have been modelled on the 1860 rebuild of USS Pocahontas
USS Unadilla under construction at the yard of John Englis, New York
USS Aroostook in Chinese waters, ca. 1867