II Corps ( Union Army ) There were five corps in the Union Army designated as II Corps ( Second Army Corps ) during the American Civil War . These formations were the Army of the Cumberland II Corps commanded by Thomas L . Crittenden from October 24 , 1862 to November 5 , 1862 , later renumbered XX Corps ; the Army of the Mississippi II corps led by William T . Sherman from January 4 , 1863 to January 12 , 1863 , renumbered XV Corps ; Army of the Ohio II Corps commanded by Thomas L . Crittenden from September 29 , 1862 to October 24 , 1862 , transferred to Army of the Cumberland ; Army of Virginia II Corps led by Nathaniel P . Banks from June 26 , 1862 to September 4 , 1862 and Alpheus S . Williams from September 4 , 1862 to September 12 , 1862 , renumbered XII Corps ; and the Army of the Potomac II Corps from March 13 , 1862 to June 28 , 1865 . Of these five , the one most widely known was the Army of the Potomac formation , the subject of this article . Corps history . The II Corps was prominent by reason of its longer and continuous service , larger organization , hardest fighting , and greatest number of casualties . Within its ranks was the regiment that sustained the largest percentage of loss in any one action ; the regiment that sustained the greatest numerical loss in any one action ; and the regiment that sustained the greatest numerical loss during its term of service . Of the one hundred regiments in the Union Army that lost the most men in battle , thirty - five of them belonged to the II Corps . The corps was organized under General Orders No . 101 , March 21 , 1862 , which assigned Brigadier General Edwin Vose Sumner to its command , and Brigadier Generals Israel B . Richardson , John Sedgwick , and Louis Blenker to the command of its divisions . Within three weeks of its organization the corps moved with George B . McClellan ' s Army of the Potomac on the Peninsula Campaign , except for Blenker ' s division , which was withdrawn on March 31 from McClellan ' s command , and ordered to reinforce John C . Frémont ' s army in western Virginia . Blenker ' s division never rejoined the corps . The remaining two divisions numbered 21 , 500 men , of whom 18 , 000 were present for duty . The first general engagement of the corps occurred at the Battle of Seven Pines , where Sumner ' s prompt and soldierly action brought the corps on the field in time to retrieve a serious disaster , and change a rout into a victory . The casualties of the two divisions in that battle amounted to 196 killed , 899 wounded , and 90 missing . In the Seven Days Battles the corps lost 201 killed , 1 , 195 wounded , and 1 , 024 missing . Upon the withdrawal of the army from before Richmond , the II Corps moved to the support of Major General John Pope ' s Army of Virginia at Second Bull Run , arriving on that field in time to go into position at the Battle of Chantilly , but was not engaged . The corps then marched on the Maryland Campaign , during which Brigadier General William H . French ' s 3rd Division was added on 10 September 1862 . At the Battle of Antietam the corps was prominently engaged , its casualties amounting to more than double that of any other corps on the field . Out of 15 , 000 effectives , it lost 883 killed , 3 , 859 wounded , and 396 missing ; total , 5 , 138 . Nearly one - half of these casualties occurred in Sedgwick ' s 2nd Division , in its bloody and ill - planned advance on the Dunker church , an affair that was under Sumner ' s personal direction ; this included units like the 34th New York Volunteer Infantry Regiment on the left flank of the division ' s 1st Brigade , as well as the 1st Minnesota Volunteer Infantry of later Gettysburg fame . The Irish Brigade , of Richardson ' s 1st Division , also sustained a terrible loss in its fight at the " Bloody Lane " , but , at the same time , inflicted a greater one on the enemy . This allowed Colonel Francis C . Barlow to lead the 61st and 64th New York Volunteer Infantry Regiment s to break through the Confederate line . Richardson was killed in this battle , and Sedgwick received three wounds . The next engagement was at the Battle of Fredericksburg . In the meantime Sumner had been promoted to the command of a Grand Division — II and IX Corps — and General Darius N . Couch , a division commander of the IV Corps , was appointed to his place . Brigadier General Winfield S . Hancock succeeded to the command of Richardson ' s 1st Division , and Brigadier General Oliver O . Howard took Sedgwick ' s place , the latter being absent on account of wounds . The loss of the corps at Fredericksburg exceeded that of any other in that battle , amounting to 412 killed , 3 , 214 wounded , and 488 missing , one - half of which fell on Hancock ' s Division in the unsuccessful assault on Marye ' s Heights . The percentage of loss in Hancock ' s Division was large , Caldwell ' s ( 1st ) Brigade losing 46 percent killed and wounded . After Fredericksburg , the Grand Divisions were discontinued and , Sumner retiring on account of age and physical disabilities , Couch remained in command . Couch led the corps at the Battle of Chancellorsville , with Hancock , John Gibbon , and French as his division commanders . Sedgwick had been promoted to the command of the VI Corps , and Howard , who had commanded Sedgwick ' s Division at Fredericksburg , was promoted to the command of the XI Corps . At Chancellorsville , the principal part of the II Corps ' fighting fell on Hancock ' s Division , its skirmish line , under Colonel Nelson A . Miles , distinguishing itself by a successful resistance to a strong attack of the enemy , making one of the most interesting episodes in the history of that battle . During the fighting at Chancellorsville , Gibbon ' s 2nd Division remained at Fredericksburg , where it supported Sedgwick ' s operations , but with slight loss . Not long after Chancellorsville , Couch was relieved at his own request , Hancock succeeding to the command of the corps , and Brigadier General John C . Caldwell to that of Hancock ' s Division . At the start of the Gettysburg Campaign , Brigadier General Alexander Hays ' brigade joined , and was assigned to the 3rd Division , Hays taking command of the division . At the Battle of Gettysburg , the corps was hotly engaged in the battles of the second and third days , encountering there the hardest fighting in its experience , and winning there its grandest laurels ; on the second day , in the fighting at the Wheatfield , and on the third , in the repulse of Pickett ' s Charge , which was mostly directed against Hancock ' s position . The fighting was deadly in the extreme , the percentage of loss in the 1st Minnesota of Gibbon ' s Division , being almost without an equal in the records of modern warfare . The loss in the corps was 796 killed , 3 , 186 wounded , and 368 missing ; a total of 4 , 350 out of less than 10 , 500 engaged . Gibbon ' s Division suffered the most , the percentage of loss in Brigadier General William Harrow ' s 1st Brigade being unusually severe . Hancock and Gibbon were seriously wounded , while of the brigade commanders , Samuel K . Zook , Edward E . Cross , George L . Willard , and Eliakim Sherrill were killed . The monthly return of the corps , June 30 , 1863 , shows an aggregate of 22 , 336 borne on the rolls , but shows only 13 , 056 " present for duty . " From the latter deduct the usual proportion of non - combatants — the musicians , teamsters , cooks , servants , and stragglers — and it becomes doubtful if the corps had over 10 , 000 muskets in line at Gettysburg . Hancock ' s wounds necessitated an absence of several months . William Hays was placed in command of the corps immediately after the battle of Gettysburg , retaining the command until August 12 , when he was relieved by Major General Gouverneur K . Warren . Warren had distinguished himself at Gettysburg by his quick comprehension of the critical situation at Little Round Top , and by the energetic promptness with which he remedied the difficulty . He had also made a brilliant reputation in the V Corps , and as the chief topographical officer of the Army of the Potomac . He was , subsequently , in command at the Battle of Bristoe Station , a II Corps affair , and one which was noticeable for the dash with which officers and men fought , together with the superior ability displayed by Warren himself . He also commanded at the Battle of Mine Run and Morton ' s Ford , the divisions at that time being under Generals Caldwell , Alexander S . Webb and Alexander Hays . Upon the reorganization of the Army of the Potomac , March 23 , 1864 , the III Corps was discontinued , and two of its three divisions were ordered transferred to the II Corps . Under this arrangement the II Corps was increased to 81 regiments of infantry and 10 batteries of light artillery . The units of the old II Corps were consolidated into two divisions , under Barlow ( now a general ) and Gibbon ; the two divisions of the III Corps were transferred intact , and were numbered as the 3rd and 4th , with Generals David B . Birney and Gershom Mott in command . By this accession , the II Corps attained in April , 1864 , an aggregate strength of 46 , 363 , with 28 , 854 present for duty . Hancock , having partially recovered from his wounds , resumed command , and led his battle - scarred divisions across the Rapidan River . In the Battle of the Wilderness , the corps lost 699 killed , 3 , 877 wounded , and 516 missing ; total , 5 , 092 , half of this loss falling on Birney ' s 3rd Division . Alexander Hays , commanding the 2nd Brigade of Birney ' s Division , was among the killed . At the Battle of Spotsylvania Court House the II Corps again attained a glorious place in history by Hancock ' s brilliant and successful assault on the morning of May 12 . During the fighting around Spotsylvania , Mott ' s 4th Division became so depleted by casualties , and by the loss of several regiments whose term of service had expired , that it was discontinued and merged into Birney ' s Division , Mott retaining the command of a brigade . The casualties of the corps in the various actions around Spotsylvania , from May 8 to May 19 , aggregated 894 killed , 4 , 947 wounded , and 801 missing ; total 6 , 642 , or over one - third of the loss in the entire Army of the Potomac , including the IX Corps . The heaviest loss occurred in Barlow ' s 1st Division . Up to this time the II Corps had not lost a color nor a gun , although it had previously captured 44 stands of colors from the enemy . After more of hard and continuous fighting at the Battle of North Anna , and along the Totopotomoy , the corps reached the memorable field where the Battle of Cold Harbor was fought . While at Spotsylvania it had been reinforced by a brigade of heavy artillery regiments , acting as infantry , and by the brigade known as the Corcoran Legion , so that at Cold Harbor it numbered 53 , 831 , present and absent , with 26 , 900 " present for duty " . Its loss at Cold Harbor including eleven days in the trenches , was 494 killed , 2 , 442 wounded , and 574 missing ; total , 3 , 510 . Birney ' s Division was but slightly engaged . In the assaults on the Petersburg entrenchments , June 16 – June 18 , the Corps is again credited with the largest casualty list . In one of these attacks , the 1st Maine Heavy Artillery sustained the greatest loss of any regimental organization in any one action during the war . At this time the corps contained 85 regiments ; its effective strength , however , was less than at a previous date . The corps recrossed the James River , and fought at Deep Bottom , July 26 , and again on August 14 ; then , having returned to the lines around Petersburg , Barlow ' s and Birney ' s Divisions were engaged at the Second Battle of Ream ' s Station , on August 25 , in which it lost a large number of men captured . At the Battle of Boydton Plank Road , October 27 , 1864 , the division commanders were Generals Thomas W . Egan and Mott , the 1st Division ( Nelson A . Miles ' s ) , being retained in the trenches . In November , 1864 , Hancock was assigned to other duty , and Major General Andrew A . Humphreys , chief of staff to the Army of the Potomac , succeeded to his position . Humphreys was in command during the final campaign , the divisions being under Generals Miles , William Hays , and Mott . The corps fought its last battle at Farmville on April 7 , 1865 , two days before Lee ' s surrender . In this final action Brigadier General Thomas A . Smyth of Hays ' 2nd Division , was killed . Smyth was an officer with a brilliant reputation , and at one time commanded the famous Irish Brigade . Recent scholarship notes the quality not just of II Corps ' leadership but its individual soldiers , addressing both individual bravery and deep commitment to the Union as depicted in letters and diaries . In spite of homesickness and coming from Democratic homes and ethnic communities which did not favor expanding war aims to emancipation , soldiers of II Corps saw the fighting through , re - enlisting in 1863 - 4 and voting overwhelmingly for Abraham Lincoln in 1864 . Pride in unit featured prominently in post - war reunions , and on the 50th anniversary of Gettysburg Speaker of the House Champ Clark from Missouri referred to soldiers of II Corps as " those unconquerable boys in blue " . Unit cohesion ultimately overcame racial antipathies , frustrations and hatreds according to this analysis .