XII Corps (ACW)
Encyclopedia
The XII Corps was a corps
Corps
A corps is either a large formation, or an administrative grouping of troops within an armed force with a common function such as Artillery or Signals representing an arm of service...

 of the Union Army
Union Army
The Union Army was the land force that fought for the Union during the American Civil War. It was also known as the Federal Army, the U.S. Army, the Northern Army and the National Army...

 during the American Civil War
American Civil War
The American Civil War was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ; the other 25...

.

The corps was formed by U.S. War Department General Order of March 13, 1862, under which the corps organization of the Army of the Potomac
Army of the Potomac
The Army of the Potomac was the major Union Army in the Eastern Theater of the American Civil War.-History:The Army of the Potomac was created in 1861, but was then only the size of a corps . Its nucleus was called the Army of Northeastern Virginia, under Brig. Gen...

 was first created. By that order, five different corps were constituted: one of which, composed of the divisions of Alpheus S. Williams
Alpheus S. Williams
Alpheus Starkey Williams was a lawyer, judge, journalist, U.S. Congressman, and a Union general in the American Civil War.-Early life:...

 and James Shields
James Shields
James Shields was an American politician and United States Army officer who was born in Altmore, County Tyrone, Ireland. Shields, a Democrat, is the only person in United States history to serve as a U.S. Senator for three different states...

 and commanded by Maj. Gen. Nathaniel P. Banks, was designated as the V Corps
V Corps (ACW)
The V Corps was a unit of the Union Army of the Potomac during the American Civil War.-1862:The corps was first organized briefly under Nathaniel P. Banks, but then permanently on May 18, 1862, designated as the "V Corps Provisional"...

. These divisions were then operating in the Shenandoah Valley
Shenandoah Valley
The Shenandoah Valley is both a geographic valley and cultural region of western Virginia and West Virginia in the United States. The valley is bounded to the east by the Blue Ridge Mountains, to the west by the eastern front of the Ridge-and-Valley Appalachians , to the north by the Potomac River...

. On June 26, President
President of the United States
The President of the United States of America is the head of state and head of government of the United States. The president leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces....

 Abraham Lincoln
Abraham Lincoln
Abraham Lincoln was the 16th President of the United States, serving from March 1861 until his assassination in April 1865. He successfully led his country through a great constitutional, military and moral crisis – the American Civil War – preserving the Union, while ending slavery, and...

 ordered that "the troops of the Shenandoah Department, now under General Banks, shall constitute the Second Army Corps" of the Army of Virginia
Army of Virginia
The Army of Virginia was organized as a major unit of the Union Army and operated briefly and unsuccessfully in 1862 in the American Civil War. It should not be confused with its principal opponent, the Confederate Army of Northern Virginia, commanded by Robert E...

. On September 12, General Order 129, it was ordered that its designation be changed to that of the XII Corps, and that Maj. Gen. Joseph K. Mansfield
Joseph K. Mansfield
Joseph King Fenno Mansfield was a career United States Army officer, civil engineer, and a Union general in the American Civil War, mortally wounded at the Battle of Antietam.-Early life:...

 be placed in command.

The XII Corps was small—only two divisions
Division (military)
A division is a large military unit or formation usually consisting of between 10,000 and 20,000 soldiers. In most armies, a division is composed of several regiments or brigades, and in turn several divisions typically make up a corps...

 instead of the customary three—but was composed of excellent material. Among its regiments were the 2nd Massachusetts, 7th Ohio, 5th Connecticut, 13th New Jersey
13th New Jersey Volunteer Infantry
The 13th New Jersey Volunteer Infantry was a Union Army regiment from New Jersey that fought in the American Civil War.-American Civil War:...

, 107th New York, 28th Pennsylvania, 46th Pennsylvania, 3rd Wisconsin, and others equally famous as crack regiments; all of them with household names in the communities from which they were recruited.

The Valley and Antietam

The corps had done considerable hard fighting under its former title. Shields's Division won a victory over Thomas J. "Stonewall" Jackson
Stonewall Jackson
ຄຽשת״ׇׂׂׂׂ֣|birth_place= Clarksburg, Virginia |death_place=Guinea Station, Virginia|placeofburial=Stonewall Jackson Memorial CemeteryLexington, Virginia|placeofburial_label= Place of burial|image=...

 at Kernstown
Battle of Kernstown I
The First Battle of Kernstown was fought on March 23, 1862, in Frederick County and Winchester, Virginia, the opening battle of Confederate Maj. Gen. Thomas J. "Stonewall" Jackson's campaign through the Shenandoah Valley during the American Civil War....

 on March 23, and Williams' Division fought well at Winchester, May 25, while on Banks' retreat. The Battle of Cedar Mountain
Battle of Cedar Mountain
The Battle of Cedar Mountain, also known as Slaughter's Mountain or Cedar Run, took place on August 9, 1862, in Culpeper County, Virginia, as part of the American Civil War. Union forces under Maj. Gen. Nathaniel P. Banks attacked Confederate forces under Maj. Gen. Thomas J...

 was also fought by this corps, alone and unassisted; and, although defeated by the overwhelming force of the enemy, the record shows that the two divisions did some of the best fighting of the war there. In that battle the divisions were commanded by Generals Williams and Christopher C. Augur
Christopher C. Augur
Christopher Columbus Augur was an American military officer, most noted for his role in the American Civil War. Although less well known than other Union commanders, he was nonetheless considered an able battlefield commander.-Early life:Augur was born in Kendall, New York. He moved with his...

; loss, 302 killed, 1,320 wounded, and 594 missing; total, 2,216, out of less than 6,000 engaged. This loss fell on four brigades, Samuel W. Crawford
Samuel W. Crawford
Samuel Wylie Crawford was a United States Army surgeon and a Union general in the American Civil War.-Early life:...

's Brigade losing 867 men out of 1679, reported by Crawford as "present in engagement". At the Second Battle of Bull Run
Second Battle of Bull Run
The Second Battle of Bull Run or Second Manassas was fought August 28–30, 1862, as part of the American Civil War. It was the culmination of an offensive campaign waged by Confederate Gen. Robert E. Lee's Army of Northern Virginia against Union Maj. Gen...

 the corps was held in reserve.

The corps participated in the Maryland Campaign
Maryland Campaign
The Maryland Campaign, or the Antietam Campaign is widely considered one of the major turning points of the American Civil War. Confederate Gen. Robert E. Lee's first invasion of the North was repulsed by Maj. Gen. George B...

 as the XII Corps, with the veteran Mansfield in command. Its division and brigade organization were the same as at Cedar Mountain; Brig. Gen. George S. Greene
George S. Greene
George Sears Greene was a civil engineer and a Union general during the American Civil War. He was part of the Greene family of Rhode Island, which had a distinguished military record for the United States. His greatest contribution during the war was his defense of the Union right flank at Culp's...

 had succeeded Augur in the command of the 2nd Division. Its depleted columns had been strengthened by the accession of five new regiments of volunteers fresh from the North, three of which were composed of Pennsylvanians enlisted for nine months only. The corps now numbered 12,300 present for duty, including the non-combatants; it contained 22 regiments of infantry and three batteries of light artillery. It was the smallest corps in the army.

It was not engaged at South Mountain
Battle of South Mountain
The Battle of South Mountain was fought September 14, 1862, as part of the Maryland Campaign of the American Civil War. Three pitched battles were fought for possession of three South Mountain passes: Crampton's, Turner's, and Fox's Gaps. Maj. Gen. George B...

, although it marched in plain view of the battle that was raging on the mountain's side, ahead of its dusty columns. At the Battle of Antietam
Battle of Antietam
The Battle of Antietam , fought on September 17, 1862, near Sharpsburg, Maryland, and Antietam Creek, as part of the Maryland Campaign, was the first major battle in the American Civil War to take place on Northern soil. It was the bloodiest single-day battle in American history, with about 23,000...

, it entered the fight early in the morning, and carried a position near, and in front of, the Dunker Church. General Mansfield fell, mortally wounded, while deploying his columns, and the command of the corps during the battle devolved on General Williams. The two divisions lost in this battle, 275 killed, 1,386 wounded, and 85 missing; total, 1,746, out of about 8,000 present in action.

The vacancy caused by the death of General Mansfield was filled by the appointment of Maj. Gen. Henry W. Slocum, a division commander of the VI Corps
VI Corps (ACW)
The VI Corps was a corps of the Union Army during the American Civil War.-Formation:The corps was organized as the Sixth Provisional Corps on May 18, 1862, by uniting Maj. Gen. William B. Franklin's Division, which had just arrived on the Virginia Peninsula, with Maj. Gen. William F. Smith's...

, who had already achieved a brilliant reputation by his services on in the Peninsula Campaign
Peninsula Campaign
The Peninsula Campaign of the American Civil War was a major Union operation launched in southeastern Virginia from March through July 1862, the first large-scale offensive in the Eastern Theater. The operation, commanded by Maj. Gen. George B...

, and at the successful storming of Crampton's Gap
Crampton's Gap
Crampton's Gap, also known as Crampton Gap, is a wind gap on South Mountain in Maryland.The gap connects Burkittsville in the Middletown Valley to the east with Gapland and Rohrersville in the Pleasant Valley to the west....

. The XII Corps remained in the vicinity of Harpers Ferry
Harpers Ferry, West Virginia
Harpers Ferry is a historic town in Jefferson County, West Virginia, United States. In many books the town is called "Harper's Ferry" with an apostrophe....

 until December, when it moved into Virginia, and made its winter quarters at Stafford Court House.

Chancellorsville and Gettysburg

The brunt of the Battle of Chancellorsville
Battle of Chancellorsville
The Battle of Chancellorsville was a major battle of the American Civil War, and the principal engagement of the Chancellorsville Campaign. It was fought from April 30 to May 6, 1863, in Spotsylvania County, Virginia, near the village of Chancellorsville. Two related battles were fought nearby on...

 fell on the XI
XI Corps (ACW)
The XI Corps was a corps of the Union Army during the American Civil War, best remembered for its involvement in the battles of Chancellorsville and Gettysburg in 1863.-Formation and the Valley Campaign:...

 and XII Corps; and yet amid all the rout and confusion of that disastrous battle the regiments of the XII Corps moved steadily with unbroken fronts, retiring at the close of the battle without the loss of a color, while the corps artillery, after having been engaged in the close fighting at the Chancellor House, withdrew in good order, taking every gun with them. In this campaign Slocum's troops were the first to cross the Rapidan River
Rapidan River
The Rapidan River, flowing through north-central Virginia in the United States, is the largest tributary of the Rappahannock River. The two rivers converge just west of the city of Fredericksburg...

, and the last to re-cross the Rappahannock River
Rappahannock River
The Rappahannock River is a river in eastern Virginia, in the United States, approximately in length. It traverses the entire northern part of the state, from the Blue Ridge Mountains in the west, across the Piedmont, to the Chesapeake Bay, south of the Potomac River.An important river in American...

. The corps at this time contained 30 regiments of infantry, with five batteries of light artillery, numbering in all 19,929 present for duty. Its losses at Chancellorsville amounted to 260 killed, 1,436  wounded, and 1,118 missing; total, 2,814. The hardest fighting and heaviest losses fell on the brigades of Brig. Gen. Thomas H. Ruger
Thomas H. Ruger
Thomas Howard Ruger was an American soldier and lawyer who served as a Union general in the American Civil War. After the war, he was a superintendent of the United States Military Academy at West Point, New York....

 and Col. Charles Candy
Charles Candy
Charles Candy was a career soldier in the United States Army who served as an officer in the volunteer Union Army during the American Civil War...

. The divisions were commanded by Generals Williams and John W. Geary
John W. Geary
John White Geary was an American lawyer, politician, Freemason, and a Union general in the American Civil War...

.

At the Battle of Gettysburg
Battle of Gettysburg
The Battle of Gettysburg , was fought July 1–3, 1863, in and around the town of Gettysburg, Pennsylvania. The battle with the largest number of casualties in the American Civil War, it is often described as the war's turning point. Union Maj. Gen. George Gordon Meade's Army of the Potomac...

, the XII Corps distinguished itself by its gallant defense of Culp's Hill on July 2–3, 1863. General Slocum was in command of the right wing at Gettysburg, which left Alpheus S. Williams, of the 1st Division, in command of the corps; Thomas H. Ruger of the 3rd Brigade, 1st Division, took Williams's place as commander of the division; Geary commanded the 2nd Division.

On the afternoon of July 2 the corps was ordered by army commander George G. Meade to disengage from Culp's Hill and reinforce the Union
Union Army
The Union Army was the land force that fought for the Union during the American Civil War. It was also known as the Federal Army, the U.S. Army, the Northern Army and the National Army...

 line on its extreme left flank, near Little Round Top. Slocum persuaded Meade to leave one brigade behind to hold the critical position: Greene's Brigade, of Geary's Division. While occupying this position on Culp's Hill, with an excessively long line to defend and no other troops in support, Greene was attacked by Edward "Allegheny" Johnson's
Edward Johnson (general)
Edward Johnson , also known as Allegheny Johnson , was a United States Army officer and a Confederate general in the American Civil War.-Early life:...

 Division, but the attack was successfully repulsed by his brigade. Greene, a civil engineer, had insisted that his men prepare impressive defensive works on the hill. Still, some of Johnson's troops effected, without opposition, a lodgment in the vacated breastworks of the XII Corps, and upon the return of those troops a desperate battle ensued to drive the Confederates
Confederate States Army
The Confederate States Army was the army of the Confederate States of America while the Confederacy existed during the American Civil War. On February 8, 1861, delegates from the seven Deep South states which had already declared their secession from the United States of America adopted the...

 out. After a long, hard fight the corps succeeded in re-occupying its works. On no part of the field did the Confederate dead lie thicker than in front of the XII Corps position. Johnson's Division, containing 22 regiments, lost in this particular action, 229 killed, 1,269 wounded, and 375 missing; total, 1,873. To this must be added the losses suffered in the 14 regiments from the brigades of William Smith, Junius Daniel
Junius Daniel
Junius Daniel was a planter and career military officer, serving in the United States Army, then in the Confederate States Army during the American Civil War, as a brigadier general. His troops were instrumental in the Confederates' success at the first day of the Battle of Gettysburg...

, and Edward A. O'Neal, which were sent to Johnson's support. The XII Corps, containing 28 regiments, lost 204 killed, 810 wounded, and 67 missing; total, 1,081.

Tennessee

At the conclusion of the Gettysburg Campaign
Gettysburg Campaign
The Gettysburg Campaign was a series of battles fought in June and July 1863, during the American Civil War. After his victory in the Battle of Chancellorsville, Confederate General Robert E. Lee's Army of Northern Virginia moved north for offensive operations in Maryland and Pennsylvania. The...

, the Army of the Potomac
Army of the Potomac
The Army of the Potomac was the major Union Army in the Eastern Theater of the American Civil War.-History:The Army of the Potomac was created in 1861, but was then only the size of a corps . Its nucleus was called the Army of Northeastern Virginia, under Brig. Gen...

 pursued Robert E. Lee
Robert E. Lee
Robert Edward Lee was a career military officer who is best known for having commanded the Confederate Army of Northern Virginia in the American Civil War....

 into Virginia, the XII Corps joining in the pursuit, and pushing forward until it reached the Rappahannock. While encamped there, on September 23, 1863, the XI
XI Corps (ACW)
The XI Corps was a corps of the Union Army during the American Civil War, best remembered for its involvement in the battles of Chancellorsville and Gettysburg in 1863.-Formation and the Valley Campaign:...

 and XII corps were detached from the army and ordered to Tennessee
Tennessee
Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...

 as a reinforcement for William Rosecrans
William Rosecrans
William Starke Rosecrans was an inventor, coal-oil company executive, diplomat, politician, and United States Army officer. He gained fame for his role as a Union general during the American Civil War...

, besieged in Chattanooga
Chattanooga, Tennessee
Chattanooga is the fourth-largest city in the US state of Tennessee , with a population of 169,887. It is the seat of Hamilton County...

. The two corps were placed under the command of Maj. Gen. Joseph Hooker
Joseph Hooker
Joseph Hooker was a career United States Army officer, achieving the rank of major general in the Union Army during the American Civil War. Although he served throughout the war, usually with distinction, Hooker is best remembered for his stunning defeat by Confederate General Robert E...

. Arriving in Tennessee, Geary's Division moved to the front, while Williams's Division was stationed along the railroad from Murfreesboro
Murfreesboro, Tennessee
Murfreesboro is a city in and the county seat of Rutherford County, Tennessee, United States. The population was 108,755 according to the United States Census Bureau's 2010 U.S. Census, up from 68,816 residents certified during the 2000 census. The center of population of Tennessee is located in...

 to Bridgeport
Bridgeport, Alabama
Bridgeport is a small city in Jackson County, Alabama, United States. At the time of 2000 census the population was 2,728. Bridgeport is included in the Huntsville-Decatur Combined Statistical Area.-History:...

. Geary pushed on in order to effect a junction with the beleaguered army at Chattanooga. On the night of October 27, his division bivouacked in Lookout Valley, in an advanced and isolated position, where he was attacked at midnight by a part of James Longstreet
James Longstreet
James Longstreet was one of the foremost Confederate generals of the American Civil War and the principal subordinate to General Robert E. Lee, who called him his "Old War Horse." He served under Lee as a corps commander for many of the famous battles fought by the Army of Northern Virginia in the...

's command. But Geary had taken proper precautions against surprise, and Longstreet was repulsed, Geary receiving in this affair a prompt and gallant support from part of the XI Corps. General George H. Thomas, commanding the Army of the Cumberland
Army of the Cumberland
The Army of the Cumberland was one of the principal Union armies in the Western Theater during the American Civil War. It was originally known as the Army of the Ohio.-History:...

, stated in his official report that "the repulse by Geary's Division of greatly superior numbers who attempted to surprise him, will rank among the most distinguished feats of arms of this war."

The midnight Battle of Wauhatchie
Battle of Wauhatchie
-References:* Boatner, Mark Mayo, III. The Civil War Dictionary. New York: McKay, 1988. ISBN 0-8129-1726-X. First published 1959 by McKay.* Cozzens, Peter. The Shipwreck of Their Hopes: The Battles for Chattanooga. Urbana: University of Illinois Press, 1994. ISBN 0-252-01922-9.* Korn, Jerry, and...

 was followed in the next month by the brilliant victory at Lookout Mountain
Battle of Lookout Mountain
The Battle of Lookout Mountain was fought November 24, 1863, as part of the Chattanooga Campaign of the American Civil War. Union forces under Maj. Gen. Joseph Hooker assaulted Lookout Mountain, Chattanooga, Tennessee, and defeated Confederate forces commanded by Maj. Gen. Carter L. Stevenson....

, where the 2nd Division fought its famous "battle above the clouds". Geary was assisted in this engagement by Walter C. Whitaker
Walter C. Whitaker
Walter Chiles Whitaker was an American farmer, attorney, and soldier. He served as an officer in the United States Army during the Mexican–American War, and also was a Union general during the American Civil War...

's Brigade of the IV Corps
IV Corps (ACW)
There were two corps of the Union Army called IV Corps during the American Civil War. They were separate units, one serving with the Army of the Potomac and the Department of Virginia in the Eastern Theater, 1862–63, the other with the Army of the Cumberland in the Western Theater,...

. One of Whitaker's regiments, the 8th Kentucky, was the first to plant its flag on the summit of the mountain.

Redesignation

In April 1864, the designation of the corps was changed to that of the XX Corps
XX Corps (ACW)
Two corps of the Union Army were called XX Corps during the American Civil War. Though both served in the Union Army of the Cumberland, they were distinct units and should be recognized as such.- McCook's Corps :...

. Generals Williams and Geary still retained command of their divisions and the men still wore their XII Corps badge. This badge (a five-pointed star, or pentagram
Pentagram
A pentagram is the shape of a five-pointed star drawn with five straight strokes...

) was adopted by the reorganized corps. The new organization was formed by the consolidation of the XI and XII corps, to which was added some minor commands. This action of the War Department was based on the small sizes of the two corps: the XI had been extremely damaged at Gettysburg and the XII had always been the smallest in the army. Nonetheless, the soldiers of the XII Corps were very upset at the loss of their original corps identity.

Upon the discontinuance of the XII Corps, General Slocum was assigned to the command of the District of Vicksburg, but resumed the corps command—of the XX Corps—during the Atlanta Campaign
Atlanta Campaign
The Atlanta Campaign was a series of battles fought in the Western Theater of the American Civil War throughout northwest Georgia and the area around Atlanta during the summer of 1864. Union Maj. Gen. William T. Sherman invaded Georgia from the vicinity of Chattanooga, Tennessee, beginning in May...

, General Hooker having been relieved. Slocum afterwards commanded the Army of Georgia
Army of Georgia
The Army of Georgia was a Union army that constituted the Left Wing of Major General William T. Sherman's Army Group during the March to the Sea and the Carolinas Campaign.-History:...

 while on the March to the Sea
Sherman's March to the Sea
Sherman's March to the Sea is the name commonly given to the Savannah Campaign conducted around Georgia from November 15, 1864 to December 21, 1864 by Maj. Gen. William Tecumseh Sherman of the Union Army in the American Civil War...

 and in the Carolinas Campaign
Carolinas Campaign
The Carolinas Campaign was the final campaign in the Western Theater of the American Civil War. In January 1865, Union Maj. Gen. William Tecumseh Sherman advanced north from Savannah, Georgia, through the Carolinas, with the intention of linking up with Union forces in Virginia. The defeat of ...

.

Command history

Alpheus S. Williams
Alpheus S. Williams
Alpheus Starkey Williams was a lawyer, judge, journalist, U.S. Congressman, and a Union general in the American Civil War.-Early life:...

            
September 12, 1862 – September 15, 1862
Joseph K. Mansfield
Joseph K. Mansfield
Joseph King Fenno Mansfield was a career United States Army officer, civil engineer, and a Union general in the American Civil War, mortally wounded at the Battle of Antietam.-Early life:...

September 15, 1862 – September 17, 1862
Alpheus S. Williams
Alpheus S. Williams
Alpheus Starkey Williams was a lawyer, judge, journalist, U.S. Congressman, and a Union general in the American Civil War.-Early life:...

September 17, 1862 – October 20, 1862
Henry W. Slocum October 20, 1862 – July 1, 1863
Alpheus S. Williams
Alpheus S. Williams
Alpheus Starkey Williams was a lawyer, judge, journalist, U.S. Congressman, and a Union general in the American Civil War.-Early life:...

July 1, 1863 – July 4, 1863
Henry W. Slocum July 4, 1863 – August 31, 1863
Alpheus S. Williams
Alpheus S. Williams
Alpheus Starkey Williams was a lawyer, judge, journalist, U.S. Congressman, and a Union general in the American Civil War.-Early life:...

August 31, 1863 – September 13, 1863
Henry W. Slocum September 13, 1863 – September 25, 1863
* Henry W. Slocum September 25, 1863 – April 18, 1864


 * Corps assigned to the Army of the Cumberland
Army of the Cumberland
The Army of the Cumberland was one of the principal Union armies in the Western Theater during the American Civil War. It was originally known as the Army of the Ohio.-History:...

; other entries assigned to the Army of the Potomac
Army of the Potomac
The Army of the Potomac was the major Union Army in the Eastern Theater of the American Civil War.-History:The Army of the Potomac was created in 1861, but was then only the size of a corps . Its nucleus was called the Army of Northeastern Virginia, under Brig. Gen...



After April 18, 1864, the divisions of the XII Corps became part of the XX Corps
XX Corps (ACW)
Two corps of the Union Army were called XX Corps during the American Civil War. Though both served in the Union Army of the Cumberland, they were distinct units and should be recognized as such.- McCook's Corps :...

.
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