Baton Rouge was first captured by Union forces in the aftermath of the fall of New Orleans (18-29 April 1862). While those forces were engaged further up the Mississippi, at Vicksburg, Union possession of the Louisiana state capitol was uncontested, but by July the tide of Union victories appeared to have ebbed, at least temporarily. The withdrawal from Vicksburg left Baton Rouge vulnerable to counterattack.
The Confederate commander at Vicksburg, General Earl van Dorn, decided to dispatch an expedition to Baton Rouge. He was encouraged by the success of the C.S.S. Arkansas against the Union fleet at Vicksburg. A similar squadron of Union gunboats was present at Baton Rouge, where they were to play a crucial role in the defence of the city. If the Arkansas could reach Baton Rouge, then those gunboats would either flee or be sunk.
Van Dorn dispatched General John Breckinridge to lead the land attack. Breckinridge was given 5,000 men, but by the time he reached Baton Rouge his effective force was only around 2,500 strong. The Union garrison of the city was about the same size. Unusually for battles in cities at this period, Baton Rouge was not strongly fortified.
The Union commander at Baton Rouge, Brigadier-General Thomas Williams, had advance warning of the Confederate attack. On the morning of 5 August his men were formed up in line of battle, ready to receive the Confederate attack. That attack went in soon after daybreak. The Union line was forced back towards the river, but there they came under the protection of their gunboats.
The Federal navy was still intact because the Arkansas never arrived. Her engines were not very good. After a journey of 300 miles, one of her engines failed within a few miles of Baton Rouge, forcing the ship onto the river bank. The ship was now stranded. When the U.S.S. Essex appeared in the river, her commander discovered that not one of her guns could be aimed at the Union ship, and so he was forced to abandon her, blowing her up to prevent her capture.
The Union gunboats now turned the tide of battle at Baton Rouge. This despite the death of General Williams, hit by a rifle ball just before he could order a counterattack. He was succeeded by Colonel Thomas W. Cahill, who launched a counterattack that forced Breckinridge to retreat. The battle was over by 10 a.m. Loses were very heavy on both sides. Union losses were 383 (84 dead, 266 wounded and 33 missing). Confederate losses were 456 (84 dead, 315 wounded and 57 missing), nearly 20% of their entire force.
Despite their victory, the Union garrison of Baton Rouge was still not safe. Breckinridge remained in the area, providing a constant threat. The Union commander in the area, Benjamin Butler, decided that the risk was too great, and on 20 August the Union garrison pulled back towards New Orleans. The city was reoccupied by Confederate force, but not for long. At the end of 1862 Butler was replaced by Nathanial Banks. His orders were to move up the Mississippi, with the hope that they would be able to join up with Grant’s forces coming down the river. Accordingly, Butler sent part of his army up the river to Baton Rouge, which they reoccupied without a fight on 17 December. The city remained in Union hands for the rest of the war. See also: Armies at Baton Rouge