A variety of flags had been designed for naval battles for the period of the Civil War; those included distinguishing marks for ships

https://jaidenbnki358.clearhavendigest.com/posts/the-many-faces-of-civil-war-flags-an-overview-of-types-and-designs-3

A style of flags were designed for naval battles during the Civil War; those integrated distinguishing marks for ships engaged in wrestle on rivers and seas alike.