The battle saw General John A. McClernand briefly rise to prominence. McClernand was a ‘political’ general (i.e. not a West Point graduate). A ‘War’ Democrat from Illinois, McClernand had convinced Lincoln that he could raise a new army capable of seizing Vicksburg if he was given command of the expedition. General Halleck was able get McClernand’s authority reduced to that of a normal corps commander, although he would still outrank Sherman through simple seniority. McClernand proved able to keep the first part of his promise, raising a series of new regiments in the north west, but his ability to command an army was as yet unproven.
At the end of 1862 Grant had launched his first attack on Vicksburg. While Grant advanced overland, Sherman was to launch a second attack from the Mississippi. McClernand had not yet arrived with the army, and so was unable to take command himself. Unfortunately, when Grant was forced to abandon his campaign, he was unable to get the news to Sherman in time to stop Sherman’s attack. This attack was repulsed with heavy losses (Battle of Chickasaw Bluffs, 29 December 1862). Sherman retreated to Milliken’s Bend, which was where McClernand joined him.
Although Union forces controlled most of the Mississippi, the Confederates still had some forces close enough to threaten the river. One such force was based at Arkansas Post, only fifty miles up the Arkansas River, which joined the Mississippi half way between Memphis and Vicksburg. Although only 5,000 strong, that force was large enough to pose a potential threat to Union communications during any attack on Vicksburg. Sherman was convinced that it was worth sending an expedition against this position, and was eventually able to persuade McClernand to approve the attack.
Once he was one over to the idea, McClernand moved his entire army of 32,000 men up the Arkansas River to attack the post. On 9 January the troops were disembarked downriver of the fort. On the following day Admiral Porter’s ironclads began to bombard the Confederate fort. Finally, on 11 January the army and navy launched a combined attack on the fort. After four hours of resistance the outnumbered Confederate garrison surrendered.
Union losses were surprisingly heavy considering their great advantage in numbers, at 134 killed, 898 wounded and 29 missing. Confederate casualties were lower, at 60 dead and 75 wounded, but they also lost 4,791 men captured. The fall of Arkansas Post also removed the Confederate’s best chance of interfering with an Union attack on Vicksburg.
Ironically, the aftermath of the battle saw the removal of McClernand, despite his initial lack of enthusiasm for the expedition. Before coming into full possession of the facts, Grant had written to General Halleck to complain about what he saw as McClernand’s wasteful diversion. Armed with Grant’s letter, Halleck was able to persuade Lincoln to allow him to issue an order giving Grant permission to remove McClernand from command of the Vicksburg expedition, and either appoint a new commander or take over himself. Meanwhile, Grant was receiving complaints about McClernand from both Sherman and Rear-Admiral David Porter. According to his autobiography, when Grant reached McClernand’s army it was clear that he had lost the confidence of both the army and navy. This gave Grant something of a problem. He would have preferred to give Sherman command of the army, but McClernand was the senior general. Grant’s solution was to take command of the Vicksburg himself, with McClernand and Sherman as Corps commanders.