On the 13th of May Banks marched from Alexandria on Simmesport, Lawler leading the infantry column, Emory next, and A. J. Smith's divisions of the Sixteenth and Seventeenth Corps bringing up the rear. As far as Fort De Russy the march followed the bank of the river, with the object of covering the withdrawal of the fleet of gunboats and transports against any possible molestation. Steele's cavalry division hung upon and harassed the rear, Polignac, Major, and Bagby hovered in front and on the flanks, while Harrison followed on the north bank of the Red River, but no serious attempt was made to obstruct the movement. On the afternoon of the 15th the Confederates were seen in force in front of the town of Marksville, but were soon driven off and retired rapidly through the town.
On the morning of the 16th of May an event took place, described by all who saw it as the finest military spectacle they ever witnessed. On the wide and rolling prairie of Avoyelles, otherwise known as the Plains of Mansura, the Confederates stood for the last time across the line of march of the retreating army. As battery after battery went into action and the cavalry skirmishers became briskly engaged, it seemed as if a pitched battle were imminent. The infantry rapidly formed line of battle, Mower on the right, Kilby Smith next, Emory in the centre, Lawler on the left, the main body of Arnold's cavalry in column on the flank. Save where here and there the light smoke from the artillery hindered the view, the whole lines of both armies were in plain sight of every man in either, but the disparity in numbers was too great to justify Taylor in making more than a handsome show of resistance on a field like this, where defeat was certain, and destruction must have followed close upon defeat; and so when our lines were advanced he prudently withdrew. Banks's losses were small, but Lieutenant Haskin's horse-battery F, 1st U. S., being unavoidably exposed in spite of its skilful handling, to a hot enfilade fire of the Confederate artillery, to cover their flank movement in retreat, suffered rather severely.
In the afternoon the troops halted for a while on the banks of a little stream to enjoy the first fresh, clear water they had so much as seen for many weeks. At the sight the men broke into cheers, and almost with one accord rushed eagerly to the banks of the rivulet. That night the army bivouacked eight miles from the Atchafalaya, and early the next morning, the 17th of May, marched down to the river at Simmesport, where the transports and the gunboats, having arrived two days earlier, lay waiting. Near Moreauville on the 17th the rear-guard of cavalry was sharply attacked by Wharton; at the same time Debray, lying in ambush with two regiments and a battery, opened fire on the flank of the moving column. While this was going on the two other regiments of Debray made a dash on the wagon-train near the crossing of Yellow Bayou, and threw it into some momentary confusion. Neither of these attacks were serious, and all were easily thrown off.
The next day, the 18th, A. J. Smith's command was in position near Yellow Bayou to cover the crossing of the Atchafalaya, and he was himself at the landing at Simmesport, in the act of completing his arrangements for crossing, when Taylor suddenly attacked with his whole force. Mower, who commanded in Smith's absence, advanced his lines as soon as he found his skirmishers coming in, and thus brought on one of the sharpest engagements of the campaign. With equal judgment, skill, and daring, Mower finally drove the Confederates off the field in confusion and with heavy loss, and so brought to a brilliant close the part borne by the gallant soldiers of the Army of the Tennessee in their trying service in Louisiana. Mower's loss was 38 killed, 226 wounded, and 3 missing, in all 267. Taylor reports his loss as about 500, including 30 killed, 50 severely wounded, and about 100 prisoners from Polignac's division. The Confederate returns account for 452 killed and wounded.
At Simmesport the skill and readiness of Bailey were once more put to good use in improvising a bridge of steamboats across the Atchafalaya. In his report, Banks speaks of this as the first attempt of the kind, probably forgetting, since it did not fall under his personal observation, that when the army moved on Port Hudson the year before, the last of the troops and trains crossed the river at the same place in substantially the same way. However, the Atchafalaya was then low: it was now swollen to a width of six hundred or seven hundred yards by the back water from the Mississippi, and thus the floating bridge, which the year before was made by lashing together not more than nine boats, with their gangways in line, connected by means of the gangplanks and rough boards, now required twenty-two boats to close the gap. Over this bridge, on the 19th of May, the troops took up their march in retreat, and so brought the disastrous campaign of the Red River to an end just a year after they had begun, in the same way and on the same spot, the triumphant campaign of Port Hudson.
On the 20th A. J. Smith crossed, the bridge was broken up, and in the evening the whole army marched for the Mississippi. On the 21st, at Red River landing, the Nineteenth Corps bade farewell to its brave comrades of the Sixteenth and Seventeenth.
A. J. Smith landed at Vicksburg on the 23d of May too late for the part assigned him in the spring campaign of Sherman's army, and the operations on the Mississippi being now reduced to the defensive, he remained on the banks of the river until called on to repulse Price's invasion of Missouri. Then, having handsomely performed his share of this service, he joined Thomas just in time to take part in the decisive battle of Nashville.
At Simmesport Banks was met by Canby, who on the 11th of May, at Cairo or on the way thence to Memphis, had assumed command of the new-made Military Division of West Mississippi, in virtue of orders from Washington, dated the 7th. The President still refused to yield to Grant's repeated requests that Banks might be altogether relieved from his command, nor did Grant longer persist in this; accordingly Banks remained the titular commander of the Department of the Gulf, with a junior officer present as his immediate superior and his next subordinate in actual command of his troops.
The Thirteenth and Nineteenth Corps, the cavalry, and the trains continued the march, under Emory, and on the 22d of May went into camp at Morganza.
From the Arkansas to the Gulf, from the Atchafalaya to the Rio Grande there was no longer a Union soldier, save the insignificant garrison kept at Brownsville to preserve the semblance of that foothold in Texas for the sake of which so much blood and treasure had been spilled into this sink of shame.