A sort of flags had been designed for naval battles for the time of the Civil War; these blanketed distinguishing marks for ships

https://emiliocwye754.valoradigest.com/posts/the-evolution-of-civil-war-flags-from-battlefield-to-display-case

A style of flags have been designed for naval battles for the duration of the Civil War; these covered distinguishing marks for ships engaged in battle on rivers and seas alike.