One of the more important technological advances at the time of the Civil War was the ability mass produce rifled barrel field artillery, increasing their accuracy and range. Smoothbore cannon were still used, falling into two categories, guns and howitzers, for firing at higher trajectories and shorter ranges. Cannons were made of cast-bronze and wood. The field artillery of the Civil War was designed to be mobile. When Union or Confederate troops marched across country, the guns moved with them. During battle, the guns were moved to assigned positions and then were switched from place to place, pulled back or sent forward as fortune demanded. The field batteries went galloping off to support an advance or repel an attack. When they withdrew, they contested the field as they went. Movement was everything. The guns could fulfill their essential function only when they could be moved where they were most needed.At the time of the Civil War, such movement required draft animals–horses, mules or oxen. Mules were excellent at pulling heavy loads, but they were not used in pulling the guns and caissons of the field artillery. No animal liked to stand under fire. In the fury of battle, horses would shy and rear and flash their hooves; but mules carried their protests to the outer limits. When exposed to fire, mules would buck and kick and roll on the ground, entangling harnesses and becoming impossible to control.