Troop engagements of the American Civil War , 1863 The following engagements took place in the year 1863 during the American Civil War . During the year , Union forces captured the Confederate cities of Vicksburg and Port Hudson , giving them complete control over the Mississippi River . History . In the Eastern theater , the Union Army of the Potomac , commanded by Major General Joseph Hooker , attacked the Confederate Army of Northern Virginia commanded by General Robert E . Lee in the Battle of Chancellorsville . Hooker planned to moved most of his army around to the Confederates ' s rear before Lee could react and force Lee to retreat but the Union army was slowed and then stopped by a small Confederate force , which was reinforced by the rest of the Confederate army . Lee then sent a flanking column led by Thomas J . Jackson around Hooker ' s left , which attacked a few hours before sunset on May 2 ; this attack and further Confederate attacks the following day forced Hooker to retreat on May 6 . During the battle , Jackson was wounded by friendly fire and died several days later . Lee reorganized his army following the campaign and launched an invasion of Union territory in June , moving through the Shenadoah Valley into Pennsylvania ; Hooker was relieved of command on June 29 , due to continuous disputes with the government over the garrison of Harpers Ferry , and replaced by Major General George Meade . During the Battle of Gettysburg from July 1 to July 3 , Meade successfully held off Lee ' s attacks while inflicting heavy casualties in return . Lee was forced to retreat back to Virginia ; Meade followed in close pursuit but was unable to find an opportunity to completely crush the Confederate army . In October , Lee attempted to isolate and destroy Meade during the Bristoe Campaign but failed in an attack on Union positions at the Battle of Bristoe Station on October 14 . Pressed by Union authorities , Meade also tried to attack Lee ' s positions along the Mine Run ; however , Lee was able to establish a fortified defensive line across the Union line of advance . Meade judged the Confederate position too strong to attack and retreated . In the Western Theater , simultaneous Union offensives from northern Mississippi and eastern Louisiana resulted in the sieges of Vicksburg and Port Hudson , both along the Mississippi River . Ulysses S . Grant started the Vicksburg campaign near the end of April when he crossed the Mississippi River near Bruinsburg Landing , south of Grand Gulf . He then marched inland and captured the Mississippi state capital of Jackson before turning east to Vicksburg ; this isolated the Confederate garrison from Confederate supplies and reinforcements . After a six week siege , the Confederate garrison surrendered on July 4 , followed by the surrender of Port Hudson on July 9 ; this resulted in the complete Union control of the Mississippi River and made Grant a hero in the North . In central Tennessee , the Union Army of the Cumberland commanded by Major General William S . Rosecrans maneuvered the Confederate Army of Tennessee , commanded by General Braxton Bragg , towards Chattanooga , Tennessee during the Tullahoma Campaign from late June to early July . In early September , Rosecrans launched another offensive which resulted in the capture of Chattanooga , an important Confederate rail center ; however , a few weeks later Bragg , reinforced with James Longstreet ' s corps from the Army of Northern Virginia , attacked Rosecrans near the Chickamauga Creek and routed much of the Union army , forcing it to retreat back to Chattanooga . Stubborn resistance from the troops of George H . Thomas prevented the Confederates from launching an immediate pursuit . Bragg settled his army into a siege of Chattanooga , almost completely cutting off all supplies to the Union army . Soon , dissension and arguments began to create tension in the Confederate army ' s high command ; this resulted in Longstreet being sent to eastern Tennessee and a reorganization of the army in an attempt by Bragg to rid the army of his critics . Grant , promoted to command of the Military Division of the Mississippi , took command of the Union forces near the city , which was reinforced by the Army of the Tennessee and a detachment from the Army of the Potomac . During the three days from November 23 to the 26 , Grant launched a series of attacks on the Confederate positions and was able to drive off Bragg ' s army . A rear guard action by Patrick Cleaburne at Ringgold Gap halted the Union pursuit long enough for Bragg to reach safety . A few weeks after the battle , Bragg was relieved of command by his own request . In the Trans - Mississippi Theater , only small battles and skirmishes took place . On January 1 , Confederate forces led by Major General John B . Magruder recaptured the port city of Galveston , the only port city which the Confederates were able to recapture during the war . In order to cut off the Trans - Mississippi supply lines to Port Hudson , Major General Nathaniel P . Banks moved up the Bayou Teche in Louisiana during April . For the remainder of the summer , Confederate commander Major General Richard Taylor attempted to cut off Banks ' supply lines to New Orleans but failed . In September , Union forces tried to invade eastern Texas to counteract the French invasion of Mexico but were defeated at Sabine Pass , losing two gunboats and 350 men while the Confederates suffered no casualties .