A sort of flags had been designed for naval battles at some point of the Civil War; these covered distinguishing marks for ships

https://cruzbuxy751.solsticebrief.com/posts/a-closer-look-at-the-most-iconic-civil-war-flags-of-the-era-2

A type of flags had been designed for naval battles during the Civil War; those protected distinguishing marks for ships engaged in strive against on rivers and seas alike.