A sort of flags were designed for naval battles for the duration of the Civil War; these protected distinguishing marks for ships

https://simonadmb548.valiantfield.com/posts/the-role-of-civil-war-flags-in-battles-and-ceremonies-2

A form of flags had been designed for naval battles throughout the time of the Civil War; these blanketed distinguishing marks for ships engaged in wrestle on rivers and seas alike.