For more than a year, Union forces struggled with difficult terrain and strong Confederate defenses protecting Vicksburg. By the end of April 1863, Major General Ulysses S. Grant's army of more than 30,000 had landed 30 miles south of the city and began an overland campaign into Mississippi. Lieutenant General John C. Pemberton, commanding 22,000 Confederates guarding Vicksburg, was caught off guard and struggled to stop the advance. On May 1 at Port Gibson, Confederates under Brigadier General John S. Bowen blocked Grant's inland movement, but after a small skirmish grew into a fierce battle, Bowen's troops evacuated the town, burned bridges, and retreated toward Vicksburg. On May 12 at Raymond, Major General John B. McPherson's column fought Brigadier General John Gregg's Confederates, who resisted for hours before retreating toward Jackson. On May 14 at Jackson, Union forces under William T. Sherman and James B. McPherson converged on the city, defeated troops commanded by Joseph E. Johnston, and after Johnston retreated north, burned factories and machine shops, cut telegraph lines, and destroyed railroad tracks before Grant turned west toward Vicksburg. On May 16 at Champion Hill, Grant's army of 32,000 fought Pemberton's 22,000 men 20 miles east of Vicksburg; after hours of desperate fighting, Pemberton retreated west, and with nearly 6,000 killed, wounded, or missing on both sides, Champion Hill became the largest and bloodiest battle of the campaign. On May 17 at Big Black River Bridge, 5,000 troops under Bowen tried to slow the pursuit by guarding a railroad bridge, but a determined Union charge broke the line, panicked soldiers fled across the river burning the bridge, and Grant captured 1,751 troops. In 20 days, Grant's army marched more than 200 miles, won five consecutive battles, drove the outnumbered Confederates back into Vicksburg's defenses, and set in motion the 47-day siege that ended with Confederate surrender on July 4, 1863.
