The 4th United States Artillery, Battery A is honored by a monument at Gettysburg and a marker at Antietam.

1861
October Consolidated with Battery C at Washington, D.C.
Duty in the Defenses of Washington, D.C. Attached to Sumner’s Division, Army of the Potomac
1862
March Moved to the Virginia Peninsula and attached to Artillery, 1st Division, 2nd Army Corps, Army of the Potomac
April 5-May 4 Siege of Yorktown
May 31-June 1 Battle of Seven Pines, Fair Oaks
June 25-July 1 Seven days before Richmond
June 29 Peach Orchard and Savage Station
June 30
White Oak Swamp and Glendale

First Lieutenant Rufus King (son of Brigadier General Rufus King) was breveted captain and later awarded the Medal of Honor for his actions in the battle. “This officer, when his captain was wounded, succeeded to the command of two batteries while engaged against a superior force of the enemy and fought his guns most gallantly until compelled to retire.”

July 1 Malvern Hill
July-August At Harrison’s Landing
August 16-28 Movement to Alexandria and Centreville
August 28-September 2 Cover Pope’s retreat
September 6-22 Maryland Campaign
September 16-17
Battle of Antietam

The batter was commanded by First Lieutenant Evan Thomas, and brought six Napoleons to the field. From Lieutenant Thomas’ official report:

On the 17th of September, 1862, I received orders to move to the front. I was halted in the woods the enemy had been driven out of that morning, and the right section was ordered into position. The rest of the battery was soon ordered into position, the same occupied by Lieutenant Kirby’s battery, and joined the right section there. I remained there without firing a shot until our left was driven back. I then changed front to fire to the left, and opened an the advancing enemy with spherical case, and then, as they approached nearer, with canister. They came on, and I would undoubtedly have lost my battery had not Franklin’s column come up at that time. I then changed to my original front, and opened with solid shot on a battery to my right, in the opposite woods, which was soon silenced. Another battery opened on me, which I saw was out of my range. A rifled battery coming up at that time, and seeing I could do no good and was only losing horses for nothing, I deemed it prudent to withdraw. I was shortly afterward ordered to the rear, to fill up, where I staid until ordered to my division. All the orders that I received were from Captain Clarke, chief of artillery, Sumner’s Corps.

All my officers and men behaved with great coolness and bravery. Several of Baxter’s Zouaves [72nd PA] helped me considerably in carrying ammunition. One was killed and one wounded. I would state that I had no infantry support during the whole engagement.”

OFFICIAL RECORDS: Series 1, Vol 19, Part 1 (Antietam – Serial 27), Page 284

From the marker at Antietam:

Batteries A and C (consolidated), 4th U.S. Artillery (6 guns) relieved Battery I, 4th U.S. Artillery just north of this point and went into position, the left of the Battery resting on this road, where it remained inactive until Greene’s Division, Twelfth Corps, was driven from the woods around the Dunkard Church, when the Battery changed front to the left, opening fire with spherical case and canister upon the charging Confederates, who, by the aid of Irwin’s Brigade and two Regiments of Hancock’s of the Sixth Corps, were repulsed. The Battery then resumed its original front and opened with solid shot upon the Confederate Artillery in the woods around and north of the Dunkard Church. Late in the day it was relieved and moved to the high ground occupied by Richardson’s Division in its assault upon the Confederates in the Sunken Lane and Piper’s Cornfield, where it remained until the morning of the 18th. 

September 22-October 30 At Harper’s Ferry
October 18 Batteries A and C separated.
October 30-November 19 Movement to Falmouth, Va.
November Assigned to Reserve Artillery, 2nd Army Corps
December 12-15
Battle of Fredericksburg
1863
January-April At Falmouth, Va.
April 27-May 6 Chancellorsville Campaign
May 1-5 Battle of Chancellorsville
May Assigned to Artillery Brigade, 2nd Army Corps
June 11-July 16 Gettysburg Campaign
July 1-3
Battle of Gettysburg
July 15 Made a Horse Battery. Assigned to 1st Brigade, Horse Artillery and attached to 1st Division, Cavalry Corps, Army of the Potomac
September 13-17 Advance to the Rapidan
September 13 Culpeper Court House
September 21-23 Reconnaissance across the Rapidan
October 9-22 Bristoe Campaign
October 12 White Sulphur Springs
October 14 Bristoe Station and St. Stephen’s Church
November 7-8 Advance to line of the Rappahannock
November 26-December 2 Mine Run Campaign
November 29 Parker’s Store
1864
May 4-June 4 Rapidan Campaign
May 5-7
Battle of the Wilderness
May 9-24 Sheridan’s Raid to the James River
May 9 North Anna River
May 11
Ground Squirrel Church and Yellow Tavern
May 12 Brook Church, Fortifications of Richmond
May 26-28 On line of the Pamunkey
May 28-31 Totopotomoy
May 31-June 1
Cold Harbor
June 4 Dismounted and sent to Washington, D.C.
June Duty in the Defenses of Washington, D.C. Attached to 1st Brigade, Hardin’s Division, 22nd Army Corps
July Assigned to Camp Barry, Defenses of Washington, D. C., 22nd Corps until August, 1865.