A form of flags had been designed for naval battles at some stage in the Civil War; those integrated distinguishing marks for ships

https://codyviqa225.northcrestbrief.com/posts/the-evolution-of-civil-war-flags-from-battlefields-to-modern-reenactments

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