Battery C is referenced on a marker at Antietam and honored by a monument at Gettysburg.

1861
September Organized in Washington. Duty in the Defenses of Washington, D. C. attached to Artillery, McCall’s Division, Army of the Potomac.
1862
March Attached to Artillery, 2nd Division, 1st Army Corps, Army of the Potomac
April Attached to Dept. of the Rappahannock
April 9-19 Advance on Falmouth, Va.
May 25-28 McDowell’s advance on Richmond
June Ordered to the Virginia Peninsula and attached to Artillery, 3rd Division, 5th Army Corps, Army Potomac
June 25-July 1 Seven days before Richmond
June 26 Mechanicsville
June 27 Gaines’ Mill
June 30 Glendale
July 1 Malvern Hill
July-August At Harrison’s Landing
August 16-28 Movement to Fort Monroe, then to Centreville, Va.
August 28-September 2 Pope’s Campaign in Northern Virginia. Attached to Artillery, 3rd Division, 3rd Corps, Army Virginia
August 29 Battle of Groveton
August 30
Second Battle of Bull Run
September 6-22 Maryland Campaign. Attached to Artillery, 3rd Division, 1st Army Corps, Army Potomac
September 14 South Mountain, Md.
September 16-17
Battle of Antietam

Commanded by Captain Dunbar Ransom, Lieutenants Weir and Gansevoort. The battery lost 2 men killed and 13 wounded.

From the War Department marker on the Antietam battlefield:

On the evening of September 16, Battery C, 5th U.S. Artillery came into battery 370 yards east of the Hagerstown Pike and opened fire on a Confederate Battery in the open field west of the Pike and north of the Dunkard Church, causing it to retire. After dark the Battery was withdrawn and bivouacked 75 yards east of J. Poffenberger’s barn.

On the morning of the 17th, the Battery advanced to a position 205 yards due east of this point and engaged the Confederate Infantry which had made a lodgement in Miller’s Cornfield. The Battery was supported by Anderson’s and Magilton’s Brigades of Meade’s Division and Gordon’s Brigade of the Twelfth Corps. After the repulse of the Confederate advance the Battery retired to its bivouac of the 16th.

October 30-November 19 Movement to Falmouth, Va.
December 12-15
Battle of Fredericksburg
January 20-24 “Mud March”
1863
February At Falmouth. Attached to Artillery, 2nd Division, 1st Army Corps
April 27-May 6 Chancellorsville Campaign
April 29-May 2 Operations at Pollock’s Mill Creek
April 29-30 Fitzhugh’s Crossing
May 1-5
Battle of Chancellorsville
May Attached to 1st Regular Brigade, Artillery Reserve, Army of the Potomac
July 1-3
Battle of Gettysburg

The battery was commanded by Lieutenant Gulian V. Weir. It brought six 12 Pounders to the field. Lieutenant Homer Baldwin was one of the wounded, struck by a fragment when an artillery chest blew up from a direct hit during the bombardment before Pickett’s Charge on July 3.

From the monument on Hancock Avenue:

July 2 Arrived at Gettysburg from near Taneytown and in the afternoon was ordered to the front and by direction of Major General W.S. Hancock took position 500 yards further to the front and by order of Brig. General John Gibbon opened fire on the Confederates on the left front. The Confederates in front advanced to within a few yards no infantry opposing. Three of the guns were captured by the Confederates and drawn off to the Emmitsburg Road but were recaptured by the 13th Vermont and another regiment.

July 3 In the rear of the line until Longstreet’s Assault was made when the Battery was moved up to Brig. General A.S. Webb’s line and opened with canister at short range on the advancing Confederates. At 6:30 p.m. returned to the Artillery Reserve.

Casualties: killed 2 men wounded 2 officers and 12 men.

July 3-15 Draft riots in New York
July At Camp Barry, Washington, D.C., 22nd Army Corps
November Consolidated with Battery I and attached to Artillery Brigade, 2nd Army Corps, Army Potomac
November 26-December 2 Mine Run Campaign
1864
May 4-June 12 Rapidan Campaign
May 5-7
Battle of the Wilderness
May 8-21
Spotsylvania Court House
May 10 Po River
May 12 Assault on the Salient
May 22-26 North Anna River
May 26-29 On line of the Pamunkey
May 28-31 Totopotomoy
June 1-12
Cold Harbor
June 16-18 Assault on Petersburg
June 16-April 2 Siege of Petersburg
June 22 Jerusalem Plank Road
July 27-29 Deep Bottom
August 18-21 Weldon Railroad
October 27-28 Boydton Plank Road, Hatcher’s Run
1865
March 25 Fort Stedman
March Attached to Artillery Reserve, Army Potomac
March 28-April 9 Appomattox Campaign
April 2 Assault on and fall of Petersburg
May Moved to Washington, D.C.
May 23 Grand Review
June Duty at Washington, D.C.