On June 28, 1863, Confederate Brig. Gen. Jean Alfred Mouton ordered Brig. Gen. Tom Green's and Col. James P. Major's brigades to take Donaldsonville. The Union had built Fort Butler, which the Rebels had to take before occupying the town. On the night of June 27, Green, within a mile and a half of the fort, began moving troops ahead to attack. The attack started soon after midnight, and the Confederates quickly surrounded the fort and began passing through the various obstructions. Unfortunately, those troops attacking along the levee came to a ditch, unknown to them, too wide to cross, that saved the day for the Union garrison. A Union gunboat, Princess Royal, came to the garrison's aid also and began shelling the attackers. Futile Confederate assaults continued for some time but they eventually ceased their operations and retired. This point on the Mississippi remained in Union hands and many other Mississippi River towns were occupied by the Yankees: the Confederates could harass but not eliminate these Union enclaves.