III Corps ( Union Army ) There were four formations in the Union Army designated as III Corps ( or Third Army Corps ) during the American Civil War . Three were short - lived : The other , the III Corps , Army of the Potomac ( March 13 , 1862 – March 24 , 1864 ) , is the subject of this article . Corps history . The III Corps included in its organization the famous Kearny Division ; also , Hooker ' s Division , the Excelsior Brigade , the Second Jersey Brigade , and other well known commands . Its brilliant record is closely interwoven with the history of the Virginia campaigns of 1862 – 1863 , in which it fought during two eventful years . Peninsula campaign : March – July 1862 . The Corps was organized March 13 , 1862 , commanded by Major General Samuel P . Heintzelman , with Generals Joseph Hooker , Charles S . Hamilton , and Fitz John Porter as its three division commanders . It was immediately ordered to join the Peninsula Campaign , Hamilton ' s Division embarking on March 17 , and leading the advance of the Army of the Potomac on that memorable campaign . During the siege of Yorktown the corps was at its maximum , the morning reports of April 30 showing an aggregate of 39 , 710 , with 64 pieces of light artillery , and 34 , 633 reported as " present for duty " . But this aggregate was maintained only briefly , as Porter ' s Division was taken away soon after to form part of the newly organized V Corps . Hamilton was relieved on April 30 , and General Philip Kearny took his place , Hamilton assuming a division command in the Army of the Mississippi . Upon the evacuation of Yorktown , the III Corps led the pursuit of the retreating enemy , attacking them at Williamsburg on May 5 , with Hooker ' s and Kearny ' s Divisions . This battle was fought almost entirely by the III Corps ; of the 2 , 239 casualties on that field , 2 , 002 occurred within its ranks ; and three - fourths of them in Hooker ' s Division , the brunt of the battle having fallen on the Excelsior Brigade and Jersey Brigade , both in Hooker ' s command . Porter ' s Division was not engaged , having been left at Yorktown ; on May 18 it was permanently detached , leaving only two divisions , Hooker ' s and Kearny ' s , in the corps , and reducing its aggregate strength to 23 , 331 present and absent , with 34 pieces of field artillery . The two divisions numbered about 17 , 000 effectives , out of the 18 , 205 reported as " present for duty " . At Fair Oaks , its next battle , 209 were killed , 945 wounded , and 91 missing , principally Charles D . Jameson ' s and Hiram G . Berry ' s Brigades of Kearny ' s Division . Five fresh regiments joined in June , increasing its report of June 20 to 27 , 474 " present and absent " , of whom 18 , 428 were reported " present for duty , equipped " ; this included eight batteries of light artillery , of 40 guns . After deducting the large number of non - combatants and detailed men that are included in the " present for duty " , the corps probably numbered at this time about 17 , 000 effectives , available in case of action . The corps made the opening fight in the Seven Days Battles , at Oak Grove , June 25 , fighting again at Glendale on June 30 , and at Malvern Hill on July 1 ; its losses in these engagements aggregated 158 killed , 1 , 021 wounded , and 794 missing ; total , 1 , 973 . The heaviest loss occurred in John C . Robinson ' s Brigade of Kearny ' s Division ; the 1st New York , Berry ' s Brigade , also encountered a hot fire at Glendale . Northern Virginia campaign : July – September 1862 . Upon the withdrawal from the front of Richmond , the III Corps accompanied the Army of the Potomac to Manassas , where it was sent to reinforce John Pope ' s Army of Virginia . The corps left Harrison ' s Bar on August 14 , and , marching to Yorktown , embarked on August 20 for Alexandria . It arrived at Warrenton Junction on August 26 , and on the following day the Excelsior Brigade had a sharp fight at Bristoe Station . On August 29 , the corps was engaged at Groveton . Cuvier Grover ' s Brigade , of Hooker ' s Division , fought desperately at the railroad embankment , in which the use of bayonets and clubbed muskets was officially reported . On the September 1 , Kearny ' s Division was engaged at Chantilly , Birney ' s Brigade taking a prominent part ; Kearny was killed in this action . The losses of the corps at Manassas , including Bristoe , Groveton , and Chantilly , amounted to 260 killed , 1 , 525 wounded , and 453 missing ; total , 2 , 238 . Hooker ' s Division numbered fully 10 , 000 men at Yorktown , and received a reinforcement of about 3 , 000 more ; after Manassas , it drew rations at Fairfax Station for only 2 , 400 men . The arduous nature of its campaigns , as well as the bullets of the enemy , had told sadly on its numbers . Fredericksburg : November – December 1862 . The corps was so reduced by its losses that it was ordered into the defenses of Washington to rest and recruit , remaining there during the Maryland Campaign , and hence was not present at the Battle of Antietam . In November it rejoined the Army of the Potomac , now under Ambrose Burnside , then on its way to Fredericksburg , and arriving at Falmouth on November 24 , encamped there until the battle of December 13 . In the meantime , General Hooker had been promoted to the command of the Center Grand Division , composed of the III and V Corps ; General George Stoneman had been assigned to the command of the III Corps ; General Birney to that of the 1st Division ; General Daniel E . Sickles to the 2nd Division ; and a third division , under General Amiel W . Whipple had been added . The corps was not prominently engaged at Fredericksburg , although under a heavy fire ; still , its casualties amounted to 145 killed , 837 wounded , and 202 missing ; total 1 , 184 , over half of which occurred in J . H . Hobart Ward ' s Brigade of Birney ' s Division . After the battle the corps returned to its quarters at Falmouth , where it spent the winter of 1862 – 1863 . General Sickles was promoted to the command of the corps , and General Hiram Berry to that of Sickles ' s Division . Chancellorsville & Gettysburg : May – July 1863 . On May 1 , 1863 , the corps broke camp and marched to Chancellorsville , an eventful field in its history ; a battle in which the brunt of the fighting fell on the III and XII Corps . It took 17 , 568 men , including non - combatants , on that campaign , losing 378 killed , 2 , 634 wounded , and 1 , 090 missing ; total 4 , 102 . Generals Berry and Whipple were among those killed . The depleted ranks were still further lessened by the loss of four New York regiments whose two - years term of enlistment had expired ; a nine - months regiment from Pennsylvania had also gone home . The corps was accordingly consolidated into two divisions ; the 1st under General David B . Birney , and the 2nd under General Andrew A . Humphreys , an able officer who had distinguished himself as a division commander at Fredericksburg . At Gettysburg , the corps took a prominent part in the battle of the second day , July 2 , 1863 . Acting against orders , General Sickles moved the corps from its assigned defensive position on Cemetery Ridge to an indefensible position about a mile forward , centered on the Peach Orchard . Sickles wanted to occupy the slightly higher ground there , but the corps was forced to defend a salient that was too long for its size . When it was attacked by two Confederate divisions , it was virtually demolished and had to be reinforced throughout the day from other corps . It did exact a fearful price from its assailants , however . Its losses at Gettysburg were 578 killed , 3 , 026 wounded , and 606 missing ; total , 4 , 210 out of less than 10 , 000 actually engaged . The morning report showed 11 , 924 present for duty equipped . General Sickles was seriously wounded , losing a leg ; he left the corps and active military service , and General Birney succeeded temporarily to the command . Autumn 1863 . In July 1863 , the corps was increased by the accession of William H . French ' s Division , which had been in garrison at Harpers Ferry and was composed , mostly , of regiments with comparatively full ranks , although they had been in service several months . General French was assigned to the command of the corps . During the pursuit of Lee , after Gettysburg , a part of the corps was engaged at Wapping Heights , Virginia , July 23 , an action in which the Excelsior Brigade was prominently engaged . Another minor affair occurred at Kelly ' s Ford , Virginia , November 7 , 1863 , in which some regiments of Birney ' s ( 1st ) Division were under fire . In the Mine Run Campaign a sharp fight took place at Locust Grove , Virginia , in which Joseph B . Carr ' s ( 3rd ) Division sustained considerable loss , the principal part of the casualties in that campaign occurring in the III Corps . At this time General French was still in command of the corps , with Generals Birney , Henry Prince , and Carr in command of the divisions . Upon the return from Mine Run , the corps went into winter quarters at Brandy Station . Army reorganization : March 1864 . On March 23 , 1864 , the War Department ordered the discontinuance of the III and I Corps ; and the amalgamation of the constiuent units of the two corps with the II , V and VI Corps . This order was much resented by many of the troops ; as a result of the resulting discontent , former soldiers of I and III Corps were permitted to wear their old corps insignia as cap badges . The 1st and 2nd Divisions were transferred to the II Corps , and , with Generals Birney and Gershom Mott in command , became respectively the 3rd and 4th Divisions of that corps . The fourth division was incorporated into the third at the Battle of Spotsylvania , and Mott became one of Birney ' s brigade commanders . The 3rd Division was transferred to the VI Corps , where , under command of General James B . Ricketts , it became the 3rd Division of that corps .