A form of flags have been designed for naval battles for the duration of the Civil War; these incorporated distinguishing marks for ships

https://lorenzoomka633.fairmontdigest.com/posts/a-closer-look-at-historic-civil-war-flags-what-they-represent

A style of flags were designed for naval battles at some point of the Civil War; those blanketed distinguishing marks for ships engaged in combat on rivers and seas alike.