Immediately after the US Civil War (1861-1865),  the "Over-The -Shoulder" configured horns which were popular for military marching bands, quickly fell out of favor as the instruments would not easily lend themselves for use at Sunday concerts in the park bandstand.  (unless the players  faced backwards!).   Some bright horn owners (and makers) therefore hedged their bets and converted OTS horns so they could be played in  bell-up or bell forward configuration.

This Bb Cornet made by Gautrot Paris and imported to the US in the 1870s, could  be played in the Key of Bb or C as well as in an OTS or Bell-up configuration by use of  clever interchangeable leadpipes (see pic below). The pigtail lowers pitch to Bb.