A variety of flags have been designed for naval battles at some stage in the Civil War; these included distinguishing marks for ships

https://mariohczd240.nexorafield.com/posts/flags-of-valor-the-significance-of-civil-war-flags-in-american-history-2

A variety of flags were designed for naval battles at some stage in the Civil War; these protected distinguishing marks for ships engaged in strive against on rivers and seas alike.