The basic unit of Union artillery was the battery, which usually consisted of six guns. Attempts were made to ensure that all six guns in a battery were of the same caliber, simplifying training and logistics. Each gun, or “piece”, was operated by a gun crew of eight, plus four additional men to handle the horses and equipment. Two guns operating under the control of a lieutenant were known as a “section”. The battery of six guns was commanded by a captain. Artillery brigades composed of five batteries were commanded by colonels and supported the infantry organizations as follows: each infantry corps was supported directly by one artillery brigade and, in the case of the Army of the Potomac, five brigades formed the Artillery Reserve. This arrangement, championed by Hunt, allowed artillery to be massed in support of the entire army’s objective, rather than being dispersed all across the battlefield. An example of the tension between infantry commanders and artillery commanders was during the massive Confederate bombardment of Cemetery Ridge on 3 July 1863, the third day of the Battle of Gettysburg. Hunt had difficulty persuading the infantry commanders, such as Maj. Gen. Winfield S. Hancock, against using all of their artillery ammunition in response to the Confederate bombardment, understanding the value to the defenders of saving the ammunition for the infantry assault to come, Pickett’s Charge.
At the start of the war, the U.S. Army had 2,283 guns on hand, but only about 10% of these were field artillery pieces. By the end of the war, the army had 3,325 guns, of which 53% were field pieces. The army reported as “supplied to the army during the war” the following quantities: 7,892 guns, 6,335,295 artillery projectiles, 2,862,177 rounds of fixed artillery ammunition, 45,258 tons of lead metal, and 13,320 tons of gunpowder.
Learn more at the Wikipedia Field artillery in the American Civil War