Van Dorn's object obviously was by crushing Williams to regain control of the Mississippi from Vicksburg to Baton Rouge, to break the blockade of Red River and to open the way for the recapture of New Orleans. Williams was expecting the attack and awaited the result with calmness.
At Baton Rouge the Mississippi washes for the last time the base of the high and steep bluffs that for so many hundreds of miles have followed the coasts of the great river and formed the contour of its left bank, overlooking its swift yellow waters and the vast lowlands of the western shore. The bluff is lower at Baton Rouge than it is above and slopes more gently to the water's edge; and here the highland draws back from the river and gradually fades away in a southeasterly direction toward the Gulf, while the surface of the country becomes more open and less broken. The stiff post-tertiary clays that compose the soil of these bluffs were in many places covered with a rich growth of timber, great magnolias and beautiful live oaks replacing the rank cottonwood and tangled willows of the lowlands, as well as the giant cypresses of the impenetrable swamps, with their mournful hangings of Spanish moss, and the wild grape binding them fast in a deadly embrace.
Six roads led out of the town in various directions. Of these the most northerly was the road from Bayou Sara. Passing behind the town its course continued toward the south along the river. Between these outstretched arms ran the road to Clinton, the Greenwell Springs road, by which the Confederates had come, the Perkins road, and the Clay Cut road.
In numbers the opposing forces were nearly equal. The Confederates went into action with about 2,600, without counting the partisan rangers and militia, numbering 400 or 500 more. Williams had about 2,500 fighting men. He had eighteen guns, the Confederates eleven. On both sides the men were enfeebled by malaria and exposure; yet the Confederates had left their sick behind, while the Union force included convalescents that came out of the hospital to take part in the battle. "There were not 1,200," said Weitzel after the battle, "who could have marched five miles. None of our men had been in battle; very few had been under fire." Among the Confederates were many of the veterans of Shiloh and more of the triumphant defenders of Vicksburg. The advantages of position was slight on either side. On the one hand Williams was forced to post his left with regard to the expected attack of the Arkansas, so that in the centre his line fell behind the camps. To offset this his right rested securely on the gunboats. As it turned out the Arkansas was not encountered, and the gunboats told off to meet her were therefore able to render material assistance on the left by their oblique fire across Williams' front.
Breckinridge commanded four picked brigades, three selected from his own division and one of Martin L. Smith's Vicksburg brigades, the whole organized in two divisions, under Brigadier-Generals Charles Clark and Daniel Ruggles. Clark had the brigades of Brigadier-General Bernard H. Helm and Colonel Thomas B. Smith, of the 20th Tennessee, with the Hudson battery and Cobb's battery. Ruggles had the brigades of Colonel A. P. Thompson, of the 3d Kentucky, and Colonel Henry W. Allen, of the 4th Louisiana, with Semmes's battery. From right to left the order of attack ran, Helm, Smith, Thompson, Allen. Clark moved on the right of the Greenwell Springs road, and Ruggles on the left. Scott's cavalry was posted on the extreme left, four guns of Semmes's battery occupied the centre of Ruggles's division, while in Clark's centre were the four guns of the Hudson battery and one of Cobb's; the other two having been disabled in a panic during the night march before the battle. On the extreme right the Clinton road was picketed and held by a detachment of infantry and rangers and the remaining section of Semmes's battery.
To meet the expected attack, Williams had posted his troops in rear of the arsenal and of the town, occupying an irregular line, generally parallel to the Bayou Sara road, and extending from the Bayou Grosse, on the left, to and beyond the intersection of the Perkins and Clay Cut roads, on the right. On the extreme left, behind the Bayou Grosse, was the 4th Wisconsin, commanded by Lieutenant-Colonel Bean. Next, but on the left bank of the bayou, stood the 9th Connecticut. Next, and on the left of the Greenwell Springs road, the 14th Maine. On the right of that road was posted the 21st Indiana, under Lieutenant-Colonel Keith, with three guns attached to the regiment, under Lieutenant J. H. Brown. Across the Perkins and Clay Cut roads the 6th Michigan was formed, under command of Captain Charles E. Clarke, while in the rear of the interval between the 6th Michigan and the 21st Indiana stood the 7th Vermont. The extreme right and rear were covered by the 30th Massachusetts in column, supporting Nims's battery, under Lieutenant Trull. On the centre and left were planted the guns of Everett's battery, under Carruth, and of Manning's 4th Massachusetts battery.
The left flank was supported by the Essex, Commander William D.
Porter; the Cayuga, Lieutenant Harrison; and the Sumter,
Lieutenant Erben; the right flank by the Kineo, Lieutenant-Commander
Ransom, and Katahdin, Lieutenant Roe.
These dispositions were planned expressly to meet the expected attack by the ram Arkansas, and in that view the arrangement was probably the best that the formation of the ground permitted. But the fighting line was very far advanced; the camps still farther; the reserve on the right was posted quite a mile and a half behind the capitol, and, as at Shiloh, no portion of the line was fortified or protected in any way, though the field was an open plain and the converging roads gave to the attacking party a wide choice of position.
About daylight Breckinridge moved to the attack in a summer fog so dense that those engaged could at first distinguish neither friend nor enemy. The blow fell first, and heavily, upon the centre and right, held by the 14th Maine, 21st Indiana, and 6th Michigan. As our troops were pressed back by the vigor of the first onset, the exposed camps of the 14th Maine, 7th Vermont, and 21st Indiana fell into the hands of the Confederates. The 9th Connecticut, with Manning's battery, moved to the support of the 14th Maine and 21st Indiana, on the right of the former, and the 4th Wisconsin formed on the left of the 14th. Further to the right, the 30th Massachusetts advanced to the support of the 21st Indiana and 6th Michigan, covering the interval between the two battalions to replace the 7th Vermont. In the first fighting in the darkness and the fog this regiment had been roughly handled; its colonel fell, a momentary confusion followed, and the regiment drifted back into a convenient position, where it was soon reformed, under Captain Porter. Nims brought his guns into battery on the right of the 6th Michigan.
The battle was short, but the fighting was severe; both sides suffered heavily, and each fell into some disorder. At different moments both wings of the Confederate force were broken, and fell back in something not very unlike panic. The colors of the 4th Louisiana were captured by the 6th Michigan. As the fog lifted, under the influence of the increasing heat, it became clear to both sides that the attack had failed. The force of the fierce Confederate outset was quite spent. The Union lines, however thinned and shattered, remained in possession of the prize. "It was now ten o'clock," says Breckinridge. "We had listened in vain for the guns of the Arkansas: I saw around me not more than 1,000 exhausted men." The battle was over. Indeed it had been over for some hours; these words probably indicate the period when the Confederate commander gave up his last hope.