The Second Missouri Volunteer Cavalry, also known officially as Merrill's Horse, was one of only a handful of Missouri regiments to be officially "named" as well as numbered.The regiment was raised under the authority of Major General John C. Frémont, commander of the Western Department of the U.S. Army, headquartered at St. Louis, Missouri. The regiment was organized by Captain Lewis Merrill, a regular Army officer and a veteran of the prewar U.S. 2nd Dragoons. Serving as a Colonel of Volunteers, Merrill organized companies of volunteers from Missouri and other western states at St. Louis's Benton Barracks. Merrill enforced a level of discipline unusual for volunteer regiments, demanding a level of professionalism comparable to U.S. Regulars.Through most of 1862, Merrill's Horse was assigned the difficult mission of fighting guerrillas and irregular Confederate cavalry in north Missouri. Often operating with Federal Missouri State Militia cavalry, the regiment established a reputation of extreme aggressiveness and effectiveness in the counter-guerrilla mission. Later in the war Merrill's Horse provided distinguished service in more conventional cavalry missions against regular Confederate units. However, in Arkansas, Tennessee, Georgia, and Alabama the regiment was repeatedly called on to return to the difficult specialist counterinsurgency mission of guerrilla fighting.The regiment ended the war guarding the railroad lines between Chattanooga and Atlanta.