The corps organization of the Confederate Army, in addition to the division, gave more general officers and greater compactness in the handling of a large army. At this time corps were unknown in the Union Army. And of still higher importance was the fact that one army came out prepared and expecting battle, with all its officers thoroughly instructed in advance as to what was expected, and the other, without such preparation, expectancy, or instruction, found itself suddenly involved against superior numbers in what proved to be the greatest battle thus far fought on the American continent. The Confederate hosts in the early morning moved to battle along their entire front with the purpose of turning either flank of the imperfectly connected Union divisions, but their efforts were, in no substantial sense, successful. The reckless and impetuous assaults, however, drove back, at first precipitately, then more slowly, the advance Union divisions, though at no time without fearful losses to the Confederates. These heavy losses made it necessary soon to draw on the Confederate reserves. The Union commanders took advantage of the undulations of the ground, and the timber, to protect their men, often posting a line in the woods on the edge of fields to the front, thus compelling their foes to advance over open ground exposed to a deadly fire. The early superiority of the attacking army wore gradually away, and while it continued to gain ground its dead and wounded were numerous and close behind it, causing, doubtless, many to straggle or stop to care for their comrades. It has been charged that much disorganization arose from the pillage of the Union captured camps. The divisions of Hurlburt and W. H. L. Wallace were soon, with the reserve artillery, actively engaged, and, save for a brief period, about 5 P.M., and immediately after, and in consequence of the capture at that hour of Prentiss and about 2000 of his division, a continuous Union line from Owl Creek to Lick Creek or the Tennessee was maintained intact, though often retired.