The 12th United States Infantry Regiment lost 8 officers and 118 enlisted men killed and mortally wounded and 3 officers and 190 enlisted men to disease during the Civil War. It is referenced on War Department markers at Antietam and honored by a monument at Gettysburg. 

1861
May 4 Organized by direction of the President
July 29 Confirmed by Act of Congress
Organized at Fort Hamilton, N.Y. Harbor
1862
March 5 Moved to Washington, D.C. Attached to Sykes’ Regular Infantry, Reserve Brigade, Army Potomac
March Moved to the Virginia Peninsula
April 5-May 4 Siege of Yorktown
May Attached to 1st Brigade, 2nd Division, 5th Army Corps
June 25-July 1 Seven days before Richmond
June 26 Battle of Mechanicsville
June 27 Gaines’ Mill
June 30 Turkey Bridge
July 1
Malvern Hill

Captain Matthew M. Blunt (USMA 1853) was breveted Major for gallantry.

July-August At Harrison’s Landing
August 16-28 Movement to Fortress Monroe, then to Centerville
August 28-September 2 Pope’s Campaign in Northern Virginia
August 29 Battle of Groveton
August 30
Second Battle of Bull Run
September 6-22 Maryland Campaign
September 16-17
Battle of Antietam

The regiment was commanded by Captain Matthew M. Blunt. The 1st Battalion lost 1 man killed and 3 wounded, while the 2nd Battalion had no casualties.

From the marker on the Antietam battlefield:

At sunset September 16, 1862, the First Battalion, Twelfth Infantry relieved the Fourth Infantry, guarding the Middle Bridge over the Antietam and remained on that duty until after noon of the 17th, when it advanced in support of the Horse Batteries posted on the crest of the ridge crossing the road a few feet west of this point. Winthrop’s Company (G) was deployed in skirmishing down the road and in the fields south of it to drive the Confederate Sharpshooters, who were annoying the gunners, and continued on this dutv until late in the day, when it was relieved by the Fourth Infantry, the Second and Tenth Infantry and the Second Battalion of the Fourteenth Infantry.

September 19-20 Shepherdstown Ford
September 21 At Sharpsburg, Md.
October 16-17 Kearneysville and Shepherdstown
October 29-November 19 Movement to Falmouth, Va.
December 12-15
Battle of Fredericksburg

Captain Matthew M. Blunt was breveted Lieutenant Colonel for gallantry.

January 20-24 “Mud March”
1863
April 27-May 6 Chancellorsville Campaign
May 1-5
Battle of Chancellorsville

Captain Thomas M. Anderson was wounded.

June 11-July 24 Gettysburg Campaign
July 1-3
Battle of Gettysburg

Commanded by Captain Thomas S. Dunn, the regiment brought eight companies to the field.

From the monument on Houck’s Ridge at Gettysburg:

July 2. Arrived in the morning and took position with the Brigade and Division near the Twelfth Corps on the right. Moved with the Division from the right to the left of the line and at 5 p.m. with the Brigade moved across Plum Run near Little Round Top and supported the Second Brigade in its advance to the crest of the rocky wooded hill in front and facing left engaged the Confederates but returned under a heavy fire on both flanks and from the rear after the Confederates had gained possession of the Wheatfield in the rear of the Brigade and went into position on Little Round Top.

July 3. Remained in the same position

July 4. Regiment with the 14th supported the 3d 4th and 6th U.S. Infantry in a reconnaissance and developed a force of the Confederate Infantry and Artillery in front.

Casualties: killed 1 officer and 7 men, wounded 4 officers and 67 men, missing 13 men.

July 5-24 Pursuit of Lee
July Companies F and H, 2nd Battalion, in N.Y. riots
August 16-19 Moved to New York
August 19 Duty at New York attached to Dept. of the East
September 14 Left New York for front
September 22 Rejoined army at Culpeper, Va. and attached to 1st Brigade, 2nd Division, 5th Army Corps
October 9-22 Bristoe Campaign
November 7-8 Advance to line of the Rappahannock
November 26-December 2 Mine Run Campaign
1864
March Attached to 4th Brigade, 1st Division, 5th Army Corps
April Attached to 1st Brigade, 1st Division, 5th Army Corps
May 5-7
Battle of the Wilderness
May 8-21
Spotsylvania Court House
May 22-26 North Anna River
May 26-28 On line of the Pamunkey
May 28-31 Totopotomoy
June 1-12
Cold Harbor
June 1-3 Bethesda Church
June Attached to 1st Brigade, 2nd Division, 5th Army Corps
June 16-18 First Assault on Petersburg
June 16 to November 2 Siege of Petersburg
July 30 Mine Explosion, Petersburg (Reserve)
August 18-21 Weldon Railroad
September 29-October 2 Poplar Springs Church, Peeble’s Farm
October 27-28 Boydton Plank Road, Hatcher’s Run
November 2-6 Moved to New York
November 1864-

July 1865

Attached to the Dept. of the East

1st Battalion on duty at Elmira, N.Y.

2nd Battalion at Fort Hamilton. N.Y. Harbor