Led by the brigade of Colonel (Brevet Brigadier General) Thomas O. Osborn and two regiments of the brigade of Colonel George B. Dandy of Brigadier General Robert S. Foster's division, the Union force formed on a low ridge south of the fort as soon as they arrived and then promptly proceeded with the assault. Colonel Harrison S. Fairchild's brigade formed as a reserve behind Osborn and Dandy's brigades. Gibbon's artillery, the Third Vermont Battery of Captain Romeo H. Start and a section of the First New York Independent Battery under Lieutenant William Sears, who were borrowed from Fort Fisher by Lieutenant Colonel Peter S. Michie because the XXIV Corps artillery had not come up yet from Hatcher's Run, silenced Fort Gregg's guns.