Andrew Cowan had seen service in Virginia before becoming an officer in an independent battery. , awaiting the order to advance on Williamsburg, May 4, 1862. File:The Photographic History of The Civil War Volume 09 Page 222.jpg|thumb|300px|Cowan's Battery at Gettysburg;of the men in this picture Sgt William E. Uhlster [A] (Second from right) was crippled and Corp Henry J Tucker [B] (3rd from left) killed -at the Battle of Cedar Creek, The 1st New York Battery was recruited by Capt Terance J. Kennedy, mostly in
Cayuga County, beginning on October 18, 1861. The battery was organized at
Auburn, New York. Andrew Cowan was commissioned as the unit's first lieutenant. The battery was mustered into the service as a volunteer unit for a term of three years on November 23. The battery arrived in
Washington, D.C., on December 4. The 1st New York Battery served at the
Battle of Yorktown and the
Battle of Williamsburg under the division's senior artillerist Capt
Romeyn B. Ayres. It took part in the
Seven Days Battles, the
Battle of South Mountain at Crampton's Gap, the
Battle of Antietam, and the
Battle of Fredericksburg. In the
Chancellorsville Campaign, the battery served in the
Second Battle of Fredericksburg, covering the crossing of VI Corps into the town of Fredericksburg. It then supported the division of BG
Albion Howe at the
Battle of Salem Church. The battery was assigned to the Artillery Brigade of VI Corps in May 1863. In that arrangement, it served in the
Battle of Gettysburg. In reserve at first, on July 3, 1863, it was placed just south of the copse of trees on Cemetery Ridge, in time to resist
Pickett's Charge. Cowan's guns filled a gap in the infantry line left when a regiment left the front. Cowan ordered his men to fire "double canister" on a group of Confederates trying to penetrate the federal line, and their fire broke up that threat. BG
Henry J. Hunt, the army's chief of artillery, was present with them and had his horse shot out from under him. A newspaper account reported that Capt Cowan served in a gun crew at the height of the assault. A monument to the battery, executed by J. G. Hamilton, stands on the site of this action. In the autumn of 1863, the battery served in the
Bristoe campaign, especially the
Second Battle of Rappahannock Station, and in the
Mine Run campaign. The battery served in the VI Corps Artillery Brigade in the
Overland Campaign and in the earliest stage of the
siege of Petersburg. Then it served with the
Army of the Shenandoah of MG
Philip Sheridan from October 1864. In Sheridan's portion of the
Valley campaigns of 1864, Cowan was wounded at the
Third Battle of Winchester. His battery saw particularly hard service at the
Battle of Cedar Creek. Cowan served briefly in
XXII Corps from December 1864 until it rejoined the Army of the Potomac on January 25, 1865. Men at the expiration of their term of service were given the chance to be discharged, but most reenlisted, permitting the battery to continue in service. In the Army of the Potomac, Capt. Cowan, who had received the
brevet rank of major, took command of the Artillery Brigade when Col
Charles Henry Tompkins was assigned to other duties. Cowan was in charge of the VI Corps guns during the
Appomattox Campaign. At the
Battle of Sailor's Creek on April 6, 1865, Cowan had gathered 20 guns near the Hillsman House. They opened fire at about 5:15 PM, experiencing no counter-battery fire from the Confederates, because their guns had not accompanied the infantry. Two divisions of VI Corps attacked the Confederate
rear guard, under Ltg
Richard S. Ewell, at about 6:00 PM. Ewell's men attacked the VI Corps divisions as they crossed the stream. The Federals were thrown back. However, Cowan's guns stopped the Southern advance, allowing the infantry to reform and counterattack. The Confederate line was hit in the front by VI Corps and in the flank by federal cavalry. It collapsed, and Ewell was among the southerners captured on the field. After
Robert E. Lee's surrender, at which he was present,{{cite book ==Post war==