While the flag was out, Cahill came up from New Orleans with the 9th Connecticut, a further detachment of the 26th Massachusetts, and the remainder of Grow's battery. This gave Stickney about 1,100 men, with four guns in position and six field-pieces. Cahill's arrival was seen by Major, who, after waiting all day in a drenching rain, began to think his condition rather critical; accordingly, at nine o'clock in the evening he set out to force his way to Brashear, where he was expecting to find Green. Riding hard, he arrived at the east bank of Bayou Boeuf late the next afternoon, and, crossing by night, at daylight on the 24th he had completely surrounded the post of Bayou Boeuf, and was just about to attack, when he saw the white flag that announced the surrender of the garrison to Mouton. Before this, Captain Julius Sanford, of the 23d Connecticut, set fire to the sugar-house filled with the baggage and clothing of the troops engaged at Port Hudson.

Meanwhile, for the surprise of Brashear, Mouton had collected thirty-seven skiffs and boats of all sorts near the mouth of the Teche, and manned them with 325 volunteers, under the lead of Major Sherod Hunter. At nightfall on the 22d of June Hunter set out, and by daylight the next morning his whole party had safely landed in the rear of the defences of Brashear, while Green, with three battalions and two batteries of his command, stood on the western bank of Berwick Bay, ostentatiously attracting the attention of the unsuspicious garrison, and three more regiments were in waiting on Gibbon's Island, ready to make use of Hunter's boats in support of his movement.

Banks meant to have broken up the great depot of military stores at Brashear, and to have removed to Algiers or New Orleans all regimental baggage and other property that had gone into store at Brashear and the Boeuf before and after the Teche campaign; such were his orders, but for some reason not easy to explain they had not been carried out. Besides the Indianians, who numbered about 30 all told, there were at Brashear four companies—D, G, I, K—of the 23d Connecticut, two companies of the 176th New York, about 150 strong, and one company, or the equivalent of a company, of the 42d Massachusetts, making in all rather less than 400 effectives; there were also about 300 convalescents, left behind by nearly thirty regiments. Notwithstanding the vast quantity of stores committed to their care, including the effects of their comrades, and in spite of all warnings, so slack and indifferent was the performance of duty on the part of the garrison of Brashear that, on the morning of the 23d of June, the reveillé was sounded for them by the guns of the Valverde battery. Thus sharply aroused, without a thought of what might happen in the rear, the garrison gave its whole attention to returning, with the heavy guns, the fire of Green's field-pieces across Berwick Bay. Soon the gunboat Hollyhock backed down the bay and out of the action, and thus it was that about half-past six Hunter's men, running out of the woods toward the railway station, and making known their presence with their rifles, took the garrison completely by surprise, and, after a short and desultory fight, more than 700 officers and men gave up their swords and laid down their arms to a little less than one half of their own number. Of the men, nearly all were well enough to march to Algiers four days later, after being paroled. Worse still, they abandoned a fortified position with 11 heavy guns—24-, 30-, and 32-pounders. The Confederate loss was 3 killed and 18 wounded. Hunter says the Union troops lost 46 killed and 40 wounded, but about this there seems to be some mistake, for the proportion is unusual, and the whole loss of the 23d Connecticut in killed and wounded was but 7, of the 176th New York but 12.

Green crossed Berwick Bay as fast as he could, and pushing on found the post at Bayou Ramos abandoned. The Union troops stationed there had retired to Bayou Boeuf, and so at daylight on the 24th, without feeling or firing a single shot, the united guards of the two stations, numbering 433 officers and men, with four guns, commanded by Lieutenant-Colonel Duganne, of the 176th New York, promptly surrendered to the first bold summons of a handful of Green's adventurous scouts riding five miles ahead of their column. Taylor now turned over the immediate command of the force to Mouton and hastened back to Alexandria to bring down Walker, in order to secure and extend his conquests. Mouton marched at once on Donaldsonville.

When the Union forces at La Fourche Crossing found the Confederates returning in such strength, they made haste to fall back on New Orleans, and were followed as far as Boutte Station by Waller's and Pyron's battalions.

On the 27th of June, Green, with his own brigade, Major's brigade, and Semmes's battery appeared before Donaldsonville, and demanded the surrender of the garrison of Fort Butler. This was a square redoubt, placed in the northern angle between the bayou and the Mississippi, designed to command and protect the river gateway to La Fourche, mounting four guns, and originally intended for a garrison of perhaps 600 men. The parapet was high and thick, like the levee, and was surrounded by a deep ditch, the flanks on the bayou and the river being further protected by stout stockades extending from the levees to the water, at ordinary stages. The work was now held by a mixed force of 180 men, comprising two small companies of the 28th Maine—F, Captain Edward B. Neal, and G, Captain Augustine Thompson,—besides a number of convalescents of various regiments. Major Joseph D. Bullen, of the 28th, was in command, and with him at the time was Major Henry M. Porter, of the 7th Vermont, provost-marshal of the parish of Iberville, whose quarters in the town on the other side of the bayou were no longer tenable.

Farragut, who had gone down to New Orleans and hoisted his flag on the Pensacola, leaving Palmer and Alden in command of the upper and lower fleets before Port Hudson, had disposed his gunboats so as to patrol the river in sections. The Princess Royal, Lieutenant-Commander M. B. Woolsey, was near Donaldsonville; the Winona, Lieutenant-Commander A. W. Weaver, near Plaquemine; and the Kineo, Lieutenant-Commander John Watters, between Bonnet Carré and the Red Church. As soon as the Confederates appeared before Donaldsonville, Woolsey was notified, and couriers were sent up and down the river to summon the Winona and the Kineo.

Green brought to the attack six regiments and one battery, between 1,300 and 1,500 strong,(2) including three regiments of his own brigade, the 4th, 5th, and 7th Texas, and three regiments of Major's brigade—Lane's, Stone's, and Phillips's. The river, and therefore the bayou, were now low, exposing wide margins of batture, and Green's plan was, while surrounding and threatening the fort on its land faces, to gain an entrance on the water front by crossing the batture and passing around the ends of the stockades.

At ten minutes past midnight the red light of a Coston signal from the fort announced to the Navy that the enemy were coming. At twenty minutes past one the fight was opened by the Confederates with musketry. Instantly the fort replied with the fire of its guns, and of every musket that could be brought to the parapet. Five minutes later the Princess Royal, which, since nightfall, had been under way and cleared for action, began shelling the woods on the right of the fort, firing a few 9-inch and 30-pounder shells over the works and down the bayou, followed presently by 30-pounder and 20-pounder shrapnel and 9-inch grape, fired at point-blank range in the direction of the Confederate yells. The assault was made in the most determined manner. Shannon, with the 5th Texas, passed some of his men around the end of the river stockade, others climbed and helped one another over, some tried to cut it down with axes, many fired through the loopholes; Phillips made a circuit of the fort and tried the bayou stockade, while Herbert's 7th Texas attempted to cross the ditch on the land side. The fight at the stockade was desperate in the extreme; those who succeeded in surmounting or turning this barrier found an impassable obstacle in the ditch, whose existence, strange to say, they had not even suspected. Here the combatants fought hand to hand; even the sick, who had barely strength to walk from the hospital to the rampart, took part in the defence. The Texans assailed the defenders with brickbats; these the Maine men threw back upon the heads of the Texans; on both sides numbers were thus injured. Lane, who was to have supported Phillips, somehow went adrift, and Hardeman, who was to have attacked the stockade on the bayou side, was delayed by his guide, but toward daylight he came up to join in the last attack. By way of a diversion, Stone had crossed the bayou to the east bank on a bridge of sugar coolers, and his part in the fight was confined to yells.

At a quarter before four the yelling, which had gone on continuously for more than two hours, suddenly died away, the fire slackened, and three rousing cheers went up from the fort. A few minutes later the Winona came down and opened fire, and at half-past four the Kineo hove in sight. The fight was ended. "The smoke clearing away," says Woolsey, "discovered the American flag flying over the fort. Gave three cheers and came to anchor." Yet the same sun rose upon a ghastly sight—upon green slopes gray with the dead, the dying, and the maimed, and the black ditch red with their blood.