To cut off the Union retreat from Brashear City, Col. James P. Major, leading an all Texas cavalry brigade traveled down the west bank of the Mississippi to Donaldsonville. He then traveled down Bayou Lafourche to Thibodaux where a small federal garrison was captured on June 20. To occupy the Union's attention away form Brashear City, a detachment of Texas Cavalry from Major's brigade attacked a Union position at Lafourche Crossing on June 21-22. The battle ended in a Union victory, but it served the Confederate purpose by keeping Union forces from reinforcing Brashear City.
Meanwhile, as the Union forces were occupied at Lafourche Crossing, Major's main force traveled to Bayou Boeuf, 8 miles east of Brashear City, and forced the surrender of a second Union garrison at that place on the 24th.
With Brashear City, Bayou Boeuf, and Thibodaux back within Confederate control, the Union forces at Lafourche Crossing were forced to retreat back to Algiers opposite New Orleans.
By the 26th, the only position still occupied by the Union in the Lafourche District was at Fort Butler opposite Donaldsonville. Major had bypassed the fort when he came down the Bayou on June 19-20.
Situated in the heart of sugar parishes, Fort Butler was a tangible reminder of Union strength during the Civil War, giving hope to Unionists and fear to secessionists. Designed by a West Point officer and constructed by freed slaves who lived in the immediate area, Fort Butler's garrison of New Englanders held firm the beliefs in the rightness of their cause, and carried with them a Puritan faith in the divine wrath and purpose of God. They had come to Louisiana to free the slaves and to impose a new system of labor based on wages and not race. Their crusade found it's expression in Fort Butler. Fort Butler was a star shaped earthen fortification, built at the confluence of Bayou Lafourche and the Mississippi between November, 1862 and February, 1863.
By late June, 1862, Fort Butler, under the command of Maj. Joseph D. Bullen, was occupied by 3 under-sized companies from the 28th Maine, and a collective group of convalescents form various regiments, including the 28th Maine, the 1st Louisiana (Union) Infantry, and the 16th New Hampshire. There were an undetermined number of blacks in the fort, as well. Who they represented is uncertain. They could have been convalescent troops from the 1st, 2nd, or 3rd Louisiana Native Guards, fighting at Port Hudson, and among the first all-black infantry regiments mustered into the Union army. On the other hand, they could have simply been freed slaves who lived in the area, and sought protection within the inner parameter of the fort. As yet, there is no Union verification of black participation during the battle, only Confederate eyewitnesses who claim seeing "blacks" fighting shoulder to shoulder along side their white Union liberators. In any case, Bullen claimed his regular force numbered fewer than 200. The Confederates wrongly assumed the fort had a larger force, including "two to three hundred Negro troops."
Not wishing to have Union forces to his rear, Gen. Mouton, whose headquarters were now in Thibodaux, ordered one of his subordinates, Brig. Gen. Thomas Green, to "take possession of the Federal fort at Donaldsonville." Leaving Thibodaux at 8:00 P.M., Friday, June 26th, Green took 6 cavalry regiments with him, totaling approximately 1,200 men. Green's troopers arrived 9 miles short of Donaldsonville by sunrise, June 27, and spent the rest of the day reconnoitering Fort Butler, interviewing local residence, and planning an attack strategy. Two of Green's subordinates, Cols. William P. Hardeman of the 4th Texas Cavalry and James P. Major (Green's brother-in-law), were opposed to the attack.
The fort was fortified with six-24-pounder siege guns. The landward side of Fort Butler had been clear cut for a distance of 900 yards. There was a brick-lined moat 16 feet wide and 12 feet deep that ran along the outer edge of the earthworks, and a stockade of upright timbers between the levee and the water's edge protected the river and bayou side of the fort. Green had been wrongly informed that the moat only extended around the southern and western edges of the fort. He thought the outer walls within the stockade were void of the moat. He was also wrongly informed that Bullen's command consisted of no fewer than 500-600 Federals. To make matters worse for Green, if he attacked during the day, he would have to contend with Union gunboats who policed the waters off Donaldsonville. Again, he was lead to believe there were four Union gunboats in the immediate waters off Donaldsonville. The truth was that there was only one during the afternoon of the 27th.
For all of these reasons, Green decided to send a messenger back to Thibodaux to ask Mouton to reconsider his order to attack Fort Butler. In the meantime, Green prepared his attack strategy hoping the battle would be called off by Mouton before he ordered his troops forward.
Knowing it would be suicide to attack Fort Butler during the day, Green ordered a rare night assault of the earthworks. The attack plan called for 3 of the 6 cavalry regiments under Major's command to attack Fort Butler from the landward side, while 1 regiment each would attack through the stockades along Bayou Lafourche and the Mississippi. The 6th regiment was ordered to cross Bayou Lafourche and enter Donaldsonville with the hopes of distracting the Federals prior to the Confederate main attack.
The afternoon of the 27th, Green sent word to Bullen asking him to surrender his post. When he refused, Green sent word back asking Bullen to evacuate all women and children for a 3 mile radius around the fort. Bullen complied, and then hastily telegraphed word back to New Orleans asking for reinforcements. Only one additional gunboat would arrive during the battle to aid Bullen in his defense.
When night fell and Green had not heard from Mouton, he wrongly assumed his commanding officer still wanted the fort taken. The truth of the matter was that Mouton had received Green's dispatch, reconsidered his order, and sent word back to Green ordering him to call off the attack. Unfortunately for Green, the order did not reach him until after the battle was concluded.
Because the Confederates were unfamiliar with the terrain around Forth Butler, and because it would be dark during the attack, local guides were called upon to direct the 6 regiments to the battlefield. Everything that could go wrong did go wrong for the Confederates that night. One of the regiments, the 1st Texas Partisan Rangers under command of Maj. Denman W. Shannon, did arrive at the stockade on the Mississippi side of the fort, but there was much difficulty in climbing over the spiked timbers. Shannon was seriously wounded while attempting to force an entrance through the stockade. Some of the 5th Texas Cavalry chose to wade through the shallow water at the end of the stockade in order to bypass the upright timbers. Once clear of the stockade, the 5th Texas was shocked to discover a moat in their path.
It was now clear that it would be impossible to scale the walls of the fort without ladders. Shannon's troopers had brought none, and were now helplessly trapped within the moat. To add to the confusion, a second regiment appeared to their rear. Col. Joseph Phillips' 3rd Texas Cavalry [Arizona Brigade] that was to attack with Lane's 1st Texas Partisan Rangers and Col. Philemon Herbert's 7th Texas Cavalry from the landward side of the fort, had moved instead to the left of their position, and joined Shannon's trapped regiment. Phillips was soon killed attempting an assault of the fort near the Mississippi stockade. Now there were 2 Confederate regiments pinned down in the moat. The Confederates could not withdraw without being picked off by the Federals firing from above them. Adding injury to insult, the Union gunboat Princess Royal, later joined by the Winoma peppered the Confederate attack form the river. Shannon and Phillips' men could do little damage to the Federals where they sat.
With Confederate casualties mounting and most of the senior officers dead or wounded, the situation inside the Mississippi stockade went from bad to worse for the Confederates. Some of the them even resorted to throwing bricks up towards the Federals, which had been loosened from the walls of the moat. The Federals responded in kind, and many of the Confederates were struck about the head form the brick missiles.
Meanwhile, Herbert's lone regiment was taking a beating of its own in front of the fort. Major, in command of the frontal assault, was wounded near the outer moat. It soon became apparent to Green that his attack was headed for a stalemate. With daylight approaching, and a third gunboat, Kineo , approaching the waters off Donaldsonville, Green knew if he stayed it meant disaster on top of the injury his army had already sustained.
Col. B. Warren Stone's 2nd Partisan Rangers, who had entered Donaldsonville prior to the start of the battle, withdrew down the bayou. Stone's men were able to direct an enfilading fire at Fort Butler from the Donaldsonville side of the bayou levee. Union artillery in the fort and the Union navy soon drove them from their positions, destroying part of Donaldsonville in the process.
At dawn on the 28th, Green sent a flag of truce to Bullen asking permission to collect his dead and wounded. Bullen denied the request, but during the negotiation many of the Confederates trapped in the moat escaped capture.
The battle was over, Green reported 40 killed, 114 wounded, and 107 missing or captured. Shannon's regiment estimated to be about 200 men lost about half of its number during the battle. In truth, the Confederate casualties may have been higher than what Green stated. Bullen reported that he buried more than 50 Confederates after the battle. Federal casualties were 8 killed, 13 wounded.
Regardless the casualties, the Battle of Fort Butler was a stunning defeat for the Confederacy, especially when you consider that there were fewer than 200 Union troops defending the fort It may have marked a milestone in the Civil War as well. With black soldiers present to some degree during the fight, it marked the first Union victory of the war using black participants. In Louisiana, anyway, it marked the first Union victory using black soldiers, and Donaldsonville shared in the accolade.