plan of attacking Vicksburg from downriver carried great risk because upon crossing the Mississippi River, his army would be beyond the reach of most of its supply lines. On April 16, Grant ordered Admiral David Dixon Porter's gunboats south under fire from the Vicksburg batteries to meet up with troops who had marched south down the west side of the river. Grant ordered diversionary battles, confusing Pemberton and allowing Grant's army to move east across the Mississippi, landing troops at Bruinsburg. Grant's army captured Jackson, the state capital. Advancing west, Grant defeated Pemberton's army at the Battle of Champion Hill on May 16, forcing their retreat into Vicksburg. After Grant's men assaulted the entrenchments twice, suffering severe losses, they settled in for a siege lasting seven weeks. During quiet periods of the campaign, Grant would take to drinking on occasion. The personal rivalry between McClernand and Grant continued until Grant removed him from command when he contravened Grant by publishing an order without permission. Pemberton surrendered Vicksburg to Grant on July 4, 1863. Vicksburg's fall gave Union forces control of the Mississippi River and split the Confederacy. By that time, Grant's political sympathies fully coincided with the Radical Republicans' aggressive prosecution of the war and emancipation of the slaves. The success at Vicksburg was a morale boost for the Union war effort. When Stanton suggested Grant be brought east to run the Army of the Potomac, Grant demurred, writing that he knew the geography and resources of the West better and he did not want to upset the chain of command in the East. Chattanooga (1863) and promotion Lincoln promoted Grant to major general in the regular army (as opposed to the volunteers) and assigned him command of the newly formed Division of the Mississippi on October 16, 1863, comprising the Armies of the Ohio, the Tennessee, and the Cumberland. After the Battle of Chickamauga, the Army of the Cumberland retreated into Chattanooga where they were partially besieged. Grant arrived in Chattanooga on horseback, after a journey by boat from Vicksburg to Cairo, and then by train to Bridgeport, Alabama. Plans to resupply the city and break the partial siege had already been set on foot before his arrival. Forces commanded by Major General Joseph Hooker, which had been sent from the Army of the Potomac, approached from the west and linked up with other units moving east from inside