During the Confederacy's late-summer and early-fall offensives in 1862, Confederate troops, under Maj. Gen. John C. Breckenridge, tried unsuccessfuly to retake Baton Rouge, Louisiana from the Union garrison there. After the failur of that attempt, Breckenridge withdrew several miles to the north and began to fortify the bluffs on the east banks of the Mississippi River at Port Hudson. As long as the Confederacy could hold fortresses at Vicksburg and Port Hudson, it could not only keep the Mississippi closed to northern commerce, but also, at least in theory, keep Union Navy warships out of the segment of river between them. That would allow the Confederacy to move large troop formations and major amounts of supplies across the river, something that would be highly problamatic if not impossible if Union vessels could patrol the entire length of the river.
Taking Port Hudson became an important object to the Union forces in the lower Mississippi Valley, headquartered at New Orleans. On March 7th, those forces, under Maj. Gen. Nathaniel P. Banks, began an advance toward Port Hudson. One week later, as Banks' forces approached Port Hudson and began to threaten the bastion's landward defenses, the cooperating naval squadron of Adm. David G. Farragut steamed upriver to run past the batteries of Port Hudson. Confederate gunnery proved surprisingly effective. The sloop-of-war U.S.S. Hartford, Farragut's flagship, and the gunboat U.S.S. Albatross successfully passed the batteries, but the U.S.S. Richmond and U.S.S. Monongahela had to drop back down river with severe damage. U.S.S. Mississippi ran aground under the deadly fire of the guns, which pounded her until she caught fire. Mississippi's crew went over the side, and the vessel burned until she exploded in mid-stream. The destruction of Mississippi was one of the most serious naval losses of the war on inland waters. Nevertheless, Farragut, with Hartford and Albatross, was now in the stretch of water that had, for the preceeding 7 months, had been free of patrolling Union warships.
Finding that he could not make any headway against Port Hudson for the time, Banks withdrew from the vicinity and turned to deal with a small Confederate army, under Lt. Gen. Richard Taylor, on the west side of the Mississippi River in the area of Bayou Teche. Between March 25-May 7, Banks campaigned in that region, chasing Taylor away, cutting off the flow of Confederate supplies through Bayou Teche to Port Hudson, and, on the 7th, occupying Alexandria, shortly after Union naval guboats had taken possession of the town. With his rear secured against harassment by Taylor, Banks could once again turn his attention to Port Hudson.
On the 14th, Banks turned down the Red River with 3 divisions toward Port Hudson, while 2 more Union divisions advanced from Baton Rouge toward the same goal. On the 21st, the Confederate commander at Port Hudson, Maj. Gen. Franklin Gardner, with a garrison of 7,000 men, made a brief foray to Plains Store in hopes of forestalling a junction of 2 Union columns. Failing, he retreated back into the Port Hudson entrenchments and presently found himself surrounded by a combined force of some 30,000 Federals on land and Farragut's warships in the river.
The prospect of a prolonged seige in the heat of a Louisiana summer, with its attendent didease, was a strong motivation for Banks to attempt to finish Port Hudson quickly. So he ordered an assault for the 27th. The effort proved to be a bloody failure. The terrain was difficult, and Banks was no great commander. His assault was uncoordinated and piecemeal, allowing Gardner to shift his troops and overcome Banks large superiority in numbers. The only bright spot for the Federals was the fact that 2 regiments of black troops, the 1st and 3rd Louisiana Native Guards, fought just as well and suffered casualties as high as their white counterparts. This was encouraging becuase it was the first major combat for black troops, and it had began to dispell the prejudice that black troops would not fight. Still, the May 27th assault was, on the whole, a disaster for Banks. Union casualties were 1,995 and Confederate casualties were 235.
After a fortnight of seige, Banks called on Gardner to surrender, but he refused. So, on June 14th, Banks launched another assault, which was more disastrous for his forces than the first one. Union casualties totaled 1,792, and Confederates, 47. The seige went on until July 7th, when Gardner received news that Vicksburg had surrendered to Grant on the 4th. The next day, Gardner agreed to surrender to Banks, and the following day, July 9th, formal surrender ceremonies took place.