Union XII Corps

      General Joseph K. Mansfield                      General Henry Warner Slocum                General Alpheus S. Williams                     General John W. Geary


General Slocum Timeline

September 24, 1827

Henry Warner Slocum is born in Delphi, Onondaga County, New York.  He is the sixth child of Matthew Barnard Slocum and Mary Ostrander Slocum.  He is named after a favorite uncle.  Henry Slocum will be one of 11 siblings.


Henry Slocum earns a public school teacher's certificate and takes charge of a county school.  He spends the next four years teaching in Woodstock, New York, and studying at the State Normal School in Albany.  He also attended Cazenovia Seminary.


The Mexican-American war begins.


Henry Slocum is appointed to West Point by Congressman Daniel F. Gott, of Onondaga, New York, from the Syracuse district.

July 1, 1848

Slocum passes the West Point entrance examination and enters West Point.

Phillip Henry Sheridan, Civil War leader and future General in chief of the Army, is Slocum's West Point roommate.  Slocum helps Sheridan prepare for his mathematics examinations.  Sheridan credits Slocum with helping him graduate from West Point.

July 1, 1852

Slocum graduates seventh in his class from the United States Military Academy at West Point.  He is commissioned as a second lieutenant in the First U.S. Artillery Regiment.  Some of Slocum's classmates are future Union generals, including George Crook, Thomas L. Casey, Alexander McCook, and David S. Stanley.

Slocum is ordered to report to Tampa Bay in south Florida.


Slocum is posted to Fort Moultrie in Charleston, South Carolina.

August 11, 1853

Henry's father, Matthew, dies at the age of 65.

February 19, 1854

Henry Slocum and Clara Rice are married in New York.


While still in the military, Slocum begins studying law.  He is taken under the tutelage of a local lawyer, B. C. Presley, who will become a South Carolina Supreme Court justice.

March 3, 1855

Slocum, serving during the Seminole War, is promoted to first lieutenant.

Soon after, Slocum's wife, Clara, gives birth to a daughter, Caroline.


The Army orders the First US Artillery to Florida.

Slocum's wife and daughter find the climate in the south to be distressing.

October 20, 1856

Slocum's daughter Caroline dies.

October 31, 1856

Slocum resigns his Army commission.  He settles in Syracuse, New York.


Slocum studies law with his brother-in-law, Leroy Morgan, a Syracuse lawyer.  He serves as an apprentice in Morgan's law office.

Slocum passes the New York Bar examination.


Slocum is admitted to the New York State Bar.

January 25, 1858

Slocum and his nephew, Thomas L. R. Morgan, decide to set up a law practice together and place an advertisement for their new law offices in Syracuse, New York.

November 2, 1858

Slocum wins election to a seat in the New York State assembly, representing the Republican Party.  He serves until the end of 1859.


Slocum volunteers as an artillery officer in the New York State militia.  He is appointed the rank of colonel.  He spends the next two years training militia in artillery tactics.


Slocum is elected as the Onondaga County Treasurer.  He wins a three year term.

April 14, 1861

Fort Sumter, in South Carolina, is attacked and put under siege by newly formed Confederate forces.

Slocum is asked to be the military advisor for Governor Morgan of New York.  Slocum declines the offer.

May 21, 1861

Slocum appointed to the Union Army as colonel of the Twenty-Eighth New York Volunteers.  Slocum appoints Joseph J. Chambers as Lieutenant Colonel and Deputy Commander, and Joseph J. Bartlett as Major.

May 1861-August 1861

Slocum commands the Twenty-Seventh Regiment of Infantry, New York Volunteers.

July 5, 1861

The Twenty-Seventh New York Volunteer Infantry is mustered into US service.  The soldiers sign up for a two year enlistment.

July 10, 1861

Slocum is ordered to take his regiment to Washington, DC, under the First Brigade of McDowell's Army Second Division.

July 16, 1861

The Twenty-Seventh New York regiment is ordered to march to Bull Run.

The regiment participates in the First Battle of Bull Run.

Slocum is wounded in the right thigh.  He is taken off the field.  Slocum is taken to Washington, DC, to recuperate.  The Union Army is routed at the First Battle of Bull Run.

July 20, 1861

Confederate Congress convenes in Richmond, Virginia.

August 9, 1861

Slocum returns to visit his regiment.  He is welcomed as a hero.

August 1861-May 1862

Slocum is promoted to the rank of Brigadier General, U.S. Army, and commands the Second Brigade of the First Division of the I Corps during the Peninsula Campaigns.  During the Seven Days Battle, he commands the First Division Sixth Corps, and later distinguishes himself at the battle of Gaines Mill.

September 7, 1861

Slocum arrives in Washington to take command of his new brigade.  It is designated the Second Brigade.  The Brigade has more than 5,000 men.

April 22, 1862

Slocum and his troops arrive and take up positions near Fort Monroe, Virginia.  They take up positions opposing Confederate General John B. Magruder, near Yorktown.

May 1862-October 1862

Slocum commands First Division of the Sixth Corps, Army of the Potomac.

July 4, 1862

Slocum is promoted to Major General.  He is one of the youngest men to achieve that rank.

Slocum is cited by Congress and the War Department for "conspicuous services rendered by him at Gaines Mill and in the movement to the James."

August 22, 1862

Robert E. Lee attacks General Pope's forces.  Slocum's division is mobilized, but is not engaged by the Confederates in the battle.  Union forces are returned to Washington.

September 17, 1862

General McClellan attacks General Lee's army at Antietam Creek, near Sharpsburg, Maryland.  Slocum's troops take up position near the Dunkard Church, at the north end of the battlefield.

The Battle of Antietam is a major victory for Lee and his Confederate forces.

October 15, 1862-April 1864

Slocum commands the Twelfth Corps of the Army of the Potomac.  Its field strength consisted of two divisions, totaling over 15,000 soldiers.

At 35 years old, Slocum is the youngest corps commander in the Union Army.

October 20, 1862

Slocum assumes command of the Twelfth Corps after Major General Joseph K. Mansfield, its commander, is killed at the battle of Antietam.

April 30, 1863

Slocum's Twelfth Corps reaches Chancellorsville.  He links with Major General George G. Meade and the Fifth Corps.

March 1, 1863

Hooker orders Slocum's Twelfth Corps forward, forming a skirmish line.  Slocum penetrates deep into Confederate lines, but is ordered to retreat.  Slocum orders his troops to build entrenchments on Friday and Saturday.

May 2, 1863

Lee deploys his and Stonewall Jackson's troops across Hooker's vulnerable front lines.  General Slocum's Twelfth Corps is deployed along the vulnerable, lightly-deployed right flank of the Union Army.

Hooker fails to capitalize on Lee's strategic retreat and misses an opportunity to defeat Lee's army.  Jackson attacks and routs Hooker's forces.  General Sickles sends his forces against Lee in a rare night battle.

Confederate General Stonewall Jackson is accidentally killed by one of his own soldiers.

May 3, 1863

Lee's forces attack Union positions.  Slocum positions the Twelfth on the extreme left of the Union Army.

May 4, 1863

In a council of war on the night of May 4, General Hooker decides to retreat.

May 5, 1863

Marching from Fredericksburg, Maryland, Lee savagely attacks Hooker's front.

May 6, 1863

Lee continues to attack Hooker's front, as Hooker begins a withdrawal.  Hooker's campaign at Fredericksburg ends in defeat.

Slocum's Twelfth Corps suffers significant losses.  Slocum loses 158 officers and 2,725 enlisted men killed, wounded or missing.  This represents 30% of his command.  Slocum blames Hooker's ineptitude for losing the Battle of Chancellorsville and his unit's losses.

Slocum and other Union generals would try to have Hooker removed from command.

May 23, 1863

Sometime before May 23, Slocum meets with President Lincoln, criticizing Hooker and his command at Chancellorsville.  He implores Lincoln, "for the sake of the Army and the Country, that [Hooker] should be relieved from the command of that Army."

Slocum threatens to resign from his command due to his anger toward Hooker.

June 1863

Lee's Army of Northern Virginia moves north and westward into the Shenandoah Valley in Northern Virginia.  Lee's plan is to penetrate deep into Pennsylvania and capture its capitol, Harrisburg, and thus cause the Union to sue for peace.

Hooker is sent in pursuit of Lee's army.

General Joseph Hooker is relieved of command.

Lincoln appoints Major General George G. Meade as Commander of the Army of the Potomac.

June 30, 1963

General George G. Meade issues the "Pipe Clay Creek" order, creating a defensive line in the hope of putting Lee in a tactical disadvantage.  Slocum receives this order around midnight.

July 1, 1863

First day of the battle of Gettysburg.

Slocum is in command of the Twelfth Corps Army of the Potomac under General Meade.

Slocum on the march arrives at Two Taverns by midday, about five miles southeast of Gettysburg.  Slocum is unaware of the heavy fighting at Gettysburg.

Around one o'clock, General O. O. Howard sends Slocum several messages requesting that Slocum move up his Twelfth Corps and take command of the Union forces at Gettysburg.  (Meade is too far from the battlefield.)  The messages are received around two o'clock.

At 3:30, Slocum begins march to Gettysburg.

Slocum takes up a position a mile from Gettysburg and takes command of the field of battle, extending the northern flank of the Union Army.  He is in command for six hours.

July 2, 1863

Second day of the battle of Gettysburg.

General Meade arrives at Gettysburg on the morning of July 2.  He posts Slocum's Twelfth Corps to a position on a ridge east-southeast of Cemetery Hill, known as Culp's Hill.  The Union Army is shaped like a fishhook, with the Twelfth forming the barbed end of the hook.  Slocum's deputy commanders are Generals Alpheus S. Williams, John W. Geary and Thomas H. Ruger.

Slocum's Twelfth Corps begins building entrenchments called breastworks.

Anticipating an attack by Lee's army, Slocum assumes temporary command of the right wing of the Union Army at Gettysburg.

Slocum's Twelfth Division comes under fire by Confederate artillery batteries.  Infantry exchange fire.  Confederate and Union troops exchange rifle fire.

Meade orders Slocum to reinforce the left wing of the Union defensive line.  This order weakens Slocum's right wing defenses.  Slocum's forces slightly outnumber the Confederates.  Slocum unsuccessfully tries to persuade Meade to amend or rescind the order.

Confederate General Joseph E. Johnston's division attacks Slocum's weakened position on Culp's Hill.

General George S. Greene, commanding a brigade under Slocum, strategically retreats and holds out the defenses until dark against superior Confederate numbers.  Greene holds his position while Johnston holds trenches and fortifications to the south.  By nightfall, the fighting stops.  By midnight, the entire Twelfth Corps has been redeployed and set in strategic defense of Culp's Hill.  This prevents Johnston from gaining ground.

Meade calls for a council of war to discuss whether the Union Army should hold or retreat to their supply lines.  General Slocum's reply becomes one of the most famous of the war: "Stay and fight it out."  Slocum advises General Williams regarding Johnston's forces on Culp's Hill, "We'll drive them out at daylight."

July 3, 1863

Third day of the battle of Gettysburg.

At 4:15 a.m., General Johnston initiates attack on Culp's Hill.  Lee hopes this will create a diversion to favor Longstreet's attack.  General John Geary successfully defends against three Confederate assaults on Culp's Hill.

At 10:30, General Johnston withdraws his command and Slocum's Twelfth Corps holds the entire right wing.  The Twelfth Corps endures 1,082 casualties with 204 men killed in action.  Slocum has lost approximately ten percent of the Twelfth's fighting force.

Slocum's successful defense of Culp's Hill is key to the Union victory at Gettysburg.

Later, General Howard praises Slocum's defense of Culp's Hill: "The fighting at Culp's Hill was the most impressive incident of the Battle of Gettysburg...a step all-important and essential to victory... Slocum... prevented Meade from losing the Battle of Gettysburg."

Lee's afternoon attack on the Union center fails.  This event marks the high water mark of the Confederate campaigns.

July 4, 1863

Lee's defeated army remains in place in his position for the entire day.

Slocum's Twelfth Corps buries 900 Confederate dead.  The Twelfth Corps is ordered to depart the battlefield.

July 5, 1863

Lee retreats with his devastated Army of Northern Virginia.

The Twelfth Corps is positioned in Littlestown, Pennsylvania, away from Lee's retreating line.

Lee's army soon escapes by crossing the Rappahannock River back to the South.

September 1863

Slocum's Twelfth Corps is ordered to Tennessee and placed under the command of General Hooker.

In a letter to President Lincoln, Slocum threatens to resign his commission because of his objection to assignment under Hooker.  Slocum meets with Lincoln on September 28.  Lincoln agrees that Slocum's Twelfth Corps will not be placed under Hooker's command.  Lincoln tells Slocum he will later be assigned to a command of equal importance away from Hooker's influence.  Lincoln writes a letter to General Rosecrans confirming this agreement.  Slocum withdraws his resignation.

October 5, 1863

Slocum and the Twelfth Corps arrive in Nashville, Tennessee.  Slocum ignores Hooker's orders and directives.

November 14, 1863

General Slocum again tenders his resignation in a letter to Secretary of War Seward because of his continued assignment under Hooker.

February 2, 1864

Slocum sends another letter asking to be taken out of the command of General Hooker.  Grant endorses the letter on February 9, recommending that Hooker be transferred.

April 18, 1864

General Slocum arrives in Vicksburg, Mississippi.  He meets with General William T. Sherman.  Sherman states, "Slocum will be a good commander for Vicksburg and Natchez."  General Grant endorses Slocum's command assignment.  Slocum commands 19,000 soldiers.  Almost half are African American soldiers (U.S. Colored Troops).

April 1864-August 1864

Slocum commands the District of Vicksburg.

August 1864-November 1864

Slocum commands the Twentieth Corps of the Army of the Cumberland, under General George H. Thomas.

October 9, 1864

Sherman sends dispatch to General Grant proposing a major campaign through the South.  This becomes "Sherman's March to the Sea."

October 18, 1864

Slocum requests of General Sherman that he be allowed to go on the campaign through Georgia.  Slocum writes, "I believe I can go through the state capital with two divisions....  I can get a new outfit of horses and mules and damage the enemy seriously by destroying the railroad, etc...."

November 5, 1864

Sherman orders Slocum to prepare his command for movement.

November 7, 1864

Sherman orders the destruction of military property in Atlanta, Georgia.

November 1864-March 1865

Slocum commands the Army of Georgia, the left wing of General William T. Sherman's Army Group.  Slocum is appointed because of his experience and his success in the occupation of Vicksburg.  Slocum's group is composed of the Fourteenth and Twentieth Corps.  The March to the Sea is planned to divide the South, draw rebel forces south and damage the Confederate economy and its ability to wage war.

November 22, 1864

Slocum's troops occupy Milledgeville, Georgia.

November 26, 1864

Slocum's Army of Georgia reaches Saundersville, Georgia.

December 10, 1864

The Army of Georgia reaches the Confederate defensive works around Savannah, Georgia.  Slocum takes up a position along the Savannah River with his right connecting to the Seventeenth Corps.

December 21, 1864

Confederate General Hardee retreats from Savannah and Slocum's troops occupy the city.  Slocum puts General Geary temporarily in charge.


Conyngham publishes Sherman's March Through the South.

February 1865

Slocum's Army of Georgia troops begin the march through South Carolina.

February 15, 1865

Slocum's Army of Georgia troops concentrate near Lexington, South Carolina.  They destroy 60 miles of rail track and head toward Columbia, the state capital.  Before Slocum's arrival, a huge fire begins in Columbia.  The fire is attributed to the actions of civilians.

March 16, 1865

Slocum's troops skirmish with Confederate soldiers near Averasboro, South Carolina.  General Hardee, the Confederate commander, puts up a stiff resistance.

March 19, 1865

Confederate General Joseph E. Johnston ambushes Slocum's wing of the Army of Georgia.  Johnston had massed his troops to stop Sherman's advance.  Slocum is able to repulse Johnston, who retreats to entrenchments.  Soon, Johnston withdraws.  This is the last battle for the Army of Georgia.

March 29, 1865

General Grant asks that the Fourteenth and Twentieth be officially designated the Army of Georgia, although they have been referred to as the Army of Georgia since September 1864.

April 2, 1865

Grant captures Richmond, Virginia.  Lee successfully withdraws his army.

April 9, 1865

Lee surrenders his Army of Northern Virginia to General Grant at the Appomattox courthouse in Virginia.

April 13, 1865

General Sherman captures Raleigh, North Carolina.

April 14, 1865

Abraham Lincoln is assassinated at Ford's Theater in Washington, DC.

General Johnston begins surrender negotiations with General Sherman.  The negotiations drag on for two weeks.  Except for small engagements, the Civil War is over.

June 1865

In a speech at his home in Syracuse, New York, Slocum said, "[Southerners] are willing to give up slavery, and only ask to be permitted to live in peace with us.  I believe it will not be difficult now to establish a new and better Union-a Union of feeling and interest.  I would treat the South with kindness, and having extinguished the last hope in the minds of all, for the continuance of slavery, I would adopt such measures as would soonest restore good feeling throughout the land."

June 6, 1865

General Slocum addresses his troops in a farewell speech, "I cannot repress a feeling of sadness at parting with you... No generation has ever done more for the establishment of a just and liberal form of government, more for the honor of their nation."

June 17, 1865

The War Department deactivates Slocum's Army of Georgia.

July 1865

General Slocum is assigned a second tour of duty in Vicksburg, Mississippi, as part of the army of occupation.  General Slocum clashes with civil governor Sharkey over policy.  Slocum's tour in Vicksburg will last less than three months.

September 16, 1865

Slocum receives offer from the Democratic Party for nomination as Secretary of State of New York.  He decides to defect from the Republican Party and accept the offer to run.  His election bid is unsuccessful.

Slocum is vilified by his former friends in the Republican Party.  They actively seek to destroy his reputation.

September 28, 1865

Slocum resigns his military commission.  He soon settles in Brooklyn, N.Y., where he continues the practice of law.


New York and Brooklyn Democrats nominate Slocum for a position of Naval Officer at New York.  His position is rejected by the Senate in 1867.


Slocum serves on New York's Electoral College as president.

In a letter to General W. T. Sherman, Slocum observes, "I cannot curse a man one day and fawn on him the next... Hence, I think  shall never make a politician."


The Brooklyn Bridge project is proposed.  Slocum is involved in the project as a member of the Brooklyn Bridge Board.

March 4, 1869-March 3, 1873

Slocum is elected as a Democrat in the Forty-first and Forty-second Congresses.  He is not a candidate in 1872.


The Brooklyn Crosstown Railroad, founded by Slocum, begins service.  It has 72 horse cars, 400 horses and 16 miles of track.  This leads to the creation of the Brooklyn and Coney Island Railroad Company.  Slocum involves his son, Henry, Jr., in the enterprise.


Slocum resumes the practice of law.


General William T. Sherman publishes his autobiography, The Memoirs of General William T. Sherman.

October 1875

Slocum creates a political reform movement against New York City boss McLaughlin.


Slocum is appointed president of the New York Board of City Works.  Slocum immediately begins to call for reform of the City Works Department.  He calls for an end to waste and graft in the department.

March 1876

Slocum and his political allies create the Kings County General Democratic Committee.  It becomes the largest Democratic club in the history of the 20th Ward.  It is nicknamed "The Slocum Committee."

September 1876

Slocum resigns from the Kings County General Democratic Committee due to lack of time and other obligations.


Slocum and fellow Commissioners on the Department of City Works reorganize and reduce the department's budget and work force.  Slocum even reduces his own salary.


Slocum's name is proposed by the Democratic Party as the nominee for Governor of New York.  Public opinion is against Slocum, and he fails to receive the nomination.

March 4, 1883-March 3, 1885

Slocum is elected as a Representative at Large from New York to the Forty-eighth Congress.


Civil War veterans elect Slocum president of the Society of the Army of the Potomac.

Late 1880s

The Brooklyn and Coney Island Railroad Company begins to electrify, replacing the horse-drawn streetcars.

February 1891

General William Tecumseh Sherman dies in New York City.  Slocum and O. O. Howard are by his side.  Slocum and Howard organize Sherman's funeral and are pall bearers.


Slocum retires as President of the Brooklyn and Coney Island Railroad Company.

April 14, 1894

Henry Warner Slocum dies in Brooklyn, New York at the age of 66. His wife, Clara, his daughter and two sons, Henry, Jr., and Clarence, are present.  Generals Sickles, Howard, Butterfield, Porter and Schofield are pallbearers.  He is interred in Greenwood Cemetery.

April 17, 1894

The Gettysburg Monument Commission, chaired by Gettysburg veteran General Sickles, passes a resolution to commission an equestrian statue of General Slocum on the Culp's Hill battlefield.


The State of New York and the City of Brooklyn name a fortification for Slocum on David's Island, New York, called Fort Slocum.

The City of New York commissions an equestrian statue of Slocum in Brooklyn.

Summer 1902

The Slocum equestrian statue in Brooklyn is completed at a total cost of $29,941.57.

September 19, 1902

General Slocum's equestrian statue is dedicated by Civil War veterans on Culp's Hill, Gettysburg battlefield.


William F. Fox publishes In Memoriam: Henry Warner Slocum (Albany, NY: J. B. Lyon). Also known as Slocum and His Men: The Twelfth Corps.


General Oliver Otis Howard publishes his memoirs.  In it, he praises General Slocum for his actions during the war.


Charles E. Slocum publishes The Life and Services of Major-General Henry Warner Slocum (Toledo: Slocum Publishing).


Liddell Hart publishes Sherman: Soldier, Realist, American.


Pfanz publishes Gettysburg: Culp's Hill and Cemetery Hill.


Brian C. Melton publishes Sherman's Forgotten General: Henry W. Slocum (Columbia, Missouri: University of Missouri Press).

September 2011

Website documenting and honoring the Army of Georgia, its officers and soldiers, is published (www.ArmyOfGeorgia.com).

July 3, 2013

The sponsors of this website innaugurate an annual reading of the names of the soldiers and officers, both Union and Confederate, who were killed at the Battle of Gettysburg.  This event takes place on the 150th anniversary of the battle.

January 2014

Website documenting and honoring American abolitionists is launched (www.AmericanAbolitionists.com).  The inspiration for the website was General Henry Warner Slocum, who was an abolitionist.

February 2014

Website documenting the Union Twelfth Corps is launched.  One of its purposes is to encourage the Department of Defense to issue retroactive Medals of Honor to officers and men of the Twelfth Corps for its actions at Culp's Hill, at the Battle of Gettysburg, July 1-3, 1863.