Vicksburg was a tough nut to crack. Her heavy guns effectively blocked the Mississippi. To the north she was defended by a vast expanse of swamps. Only to the south was there dry ground suitable for the movement of large armies. Grant decided to bypass those swamps by marching much further east, away from the river, and then swinging west once he was level with the city. At the same time General Sherman would lead a diversionary attack down the Mississippi River. The two armies would attack at the same time, forcing Pemberton, the Confederate commander at Vicksburg, to split his forces.
The main weakness with this plan was that there was little or no chance of Grant getting any urgent messages through to Sherman. Thus when a Confederate cavalry force under Earl Van Dorn destroyed Grant’s supply depot at Holy Springs on 20 December forced Grant to abandon his part of the expedition he was unable to get the news to Sherman in time.
In the meantime Sherman had successfully reached Chickasaw Bayou, just north of Vicksburg, with an army 32,000 strong. He was to attack the bluffs that marked the edge of the swamp. On those hills Pemberton was able to deploy 14,000 men, secure in the knowledge that his rear was entirely secure.
On 29 December Sherman launched his attack. It was a total failure, one of the most one-sided Confederate victories of the war (even more so than Sherman’s other main failure, at Kenesaw Mountain in 1864). Attacking up a slope against well dug-in defenders very rarely succeeded during the Civil War, and this was no exception. Pemberton’s men suffered 207 losses (63 dead, 134 wounded and 10 missing), while Sherman’s suffered 1,776 (208 dead, 1,005 wounded and 563 wounded), eight times as many losses despite a numerical advantage of over two-to-one.
Sherman was forced to abandon the attack and retreat up the Mississippi River. A further indignity then followed. The quick departure of his expedition had prevented General John McClernand from arriving in time to replace him in charge of the army on the Mississippi. Sherman retreated to Milliken’s Bend, where he found McClernand had now arrived. Sherman was reduced to the role of corps commander in McClernand’s army.