A kind of flags were designed for naval battles at some stage in the Civil War; these covered distinguishing marks for ships

https://deanrshx384.summitviewdaily.com/posts/a-closer-look-on-the-most-iconic-civil-war-flags-of-the-era-2

A kind of flags were designed for naval battles for the duration of the Civil War; these included distinguishing marks for ships engaged in wrestle on rivers and seas alike.