The trombone was a bit of a problem for cavalries...
Trombones were straight tubes up until around the 12th or 13th century, when some unknown craftsman came upon the idea of bending a piece of tubing that was too long, and then attaching a U-shaped slide to it. Even so, there is an interesting story about trombones being too long. In the 19th century someone came up with the idea of a "short trombone" for members of cavalry bands. In this instrument, the slide was replaced with a valve. It was very difficult to maintain one's balance on horseback while playing a slide trombone, and many players are known to have fallen from their mounts. In most modern marching bands the trombone player marches in front, so that he or she doesn't hit anyone with the long slide of the instrument.
(Reference: Alyn Shipton (Author), Reiko Irie (Translator), "Illustrated World of Music 3: Brass Instruments," Kaiseishakan, 1994)