The battle of Boonsboro Gap was not anticipated by General Lee, and it came, on the 14th, in the nature of a surprise.
Certainly Lee's army was not prepared for it. All that could be done was done—the brigades of Hill and Longstreet, with such artillery as could be operated on the mountain, held back the advancing columns of Hooker and Reno until night put an end to the conflict.
General McClellan reported the battle on his side as fought by the divisions of Hatch, Ricketts and Meade, of Hooker's corps; Willcox, Sturgis and Cox, of Reno's corps; and the brigade of Sedgwick, of Sherman's corps; with artillery and cavalry.
That this force did not drive Hill in rout from the mountain before Longstreet came up is due to the firmness and heroism of his defense.
That it did not envelop both Longstreet and Hill late in the afternoon, and force them down upon Boonsboro, is due to the skill of those generals, and the conduct of their troops and their commanders.