This is almost certainly a yacht owners burgee or a private shipping company's flag or a paddle wheel steamer flag or some other sort of steamship flag. I have been through many copies of Lloyd's Register and other similar books, but I cannot find it. The flag is circa 1880 or after I would guess. Might be 1870's. It was claimed to be a Civil War corps flag, but it is not. Corps flags were silk and 6 feet or so in length and made of silk, and had very specific designs. This flag is wool and made for nautical use.