The 12th cavalry was a unit in the Independent Planets military. The unit participated in many battles during the Unification War, equipped with the Firefly Series 3 military variant. Using specialized hit and run tactics, the 12th cavalry was a major part of why the Browncoats had near unchallenged control of the skies during the first part of the war.
It's unknown if this unit participated in the Battle of Sturges, which made the gunboats they used all but obsolete.