A style of flags were designed for naval battles during the Civil War; those protected distinguishing marks for ships

https://manuelasvb291.keystonescope.com/posts/preserving-history-the-importance-of-reenactment-quality-civil-war-flags-2

A sort of flags were designed for naval battles all the way through the Civil War; those protected distinguishing marks for ships engaged in struggle on rivers and seas alike.