The battery is referenced on a War Department marker at Antietam and honored by a monument at Gettysburg

1861
January At San Francisco under the command of Captain Edward O.C. Ord
October 14 Ordered to New York, then moved to Washington, D.C.
November Duty in the Defenses of Washington, D. C. attached to Artillery Reserve, Army of the Potomac
1862
March Moved to the Virginia Peninsula.
April 5-May 4 Siege of Yorktown
May Attached to Battery G. Attached to 1st Brigade, Horse Artillery, Artillery Reserve, 5th Army Corps, Army of the Potomac
June 25-July 1 Seven days before Richmond
June 26-July 2 Operations about White House
July Rejoined army via Gloucester Point.
August 5 Malvern Hill
September 6-22 Maryland Campaign. Attached to Artillery, Cavalry Division, Army of the Potomac
September 13 Middletown, Md.
September 16-17
Battle of Antietam

The battery was commanded by Captain Horatio G. Gibson and was armed with six 3-inch Ordnance Rifles.

From the marker at Antietam:

Horse Batteries C and G (consolidated), 3d U.S. Artillery, crossed the Antietam in the forenoon of September 17, and went into position a short distance south of this point, on the left of Battery M, 2d U.S. Artillery, and the right of Batteries B and L (consolidated), 2d U.S. Artillery. After an engagement of nearly two hours it was relieved by Battery E, 1st U.S. Artillery, and withdrawn east of the Antietam, taking up its second position on the ridge north of the Boonsboro Pike.

September 19 Shepherdstown Ford
October Battery G broken up
October 31 Aldie and Mountsville
November Attached to Bayard’s Cavalry Brigade, Army of the Potomac
November 4 New Baltimore, Salem and Thoroughfare Gap
November 7-9 Rappahannock Station
December 12-15
Battle of Fredericksburg
1863
February Attached to Artillery Reserve, Army of the Potomac
April 27-May 6 Chancellorsville Campaign
May 1-5
Battle of Chancellorsville
May Attached to 2nd Regular Brigade, Artillery Reserve, Army of the Potomac
June Attached to 2nd Brigade, Horse Artillery, Army of the Potomac
June 9
Battle of Brandy Station

Commanded by Lieutenant William D. Fuller, the battery was attached to a temporarily composite infantry brigade that supported the Cavalry Corps.

June 17 Aldie
June 19 Middleburg
June 22 Upperville
July 1-3
Battle of Gettysburg

From the monument on Taneytown Road at Gettysburg:

Six 3 inch Rifles
Lieut. William D. Fuller commanding

July 1. Proceeded under orders to Manchester Md. and picketed and held roads until afternoon of July 3 when ordered to Emmitsburg and marched to Westminster.

July 4. Arrived at Emmitsburg Not engaged

July 5 Smithburg, Md.
July 10-13 Jones’ Cross Roads, near Williamsport
September 23 Robertson’s Ford
October 9-22 Bristoe Campaign
November 7-8 Advance to line of the Rappahannock
November 7-8 Rappahannock Bridge
November 26-December 2 Mine Run Campaign
1864
February 28-
March 4
Kilpatrick’s Raid on Richmond
March 1 Fortifications of Richmond
March Consolidated with Batteries F and K
May 4-June 12 Rapidan Campaign
May 5-7
Battle of the Wilderness
May 8-21
Battle of Spotsylvania Court House
May 27 Salem Church
June 1-12
Cold Harbor
June 16 –
August 5
Siege of Petersburg
July 27-28 Deep Bottom
August 7-
November 28
Sheridan’s Shenandoah Campaign. Attached to Horse Artillery, Army of the Shenandoah, Middle Military Division
August 11 Near Winchester
August 25 Near Kearneysville
October 19
Battle of Cedar Creek
December Duty in the Shenandoah Valley attached to Horse Artillery, Reserve, Army of the Shenandoah
1865
April In Defenses of Washington attached to Horse Artillery Brigade, 22nd Army Corps until August