When Lee’s outposts near Antietam Creek informed him in midafternoon that Hooker’s Federals were massing north of Sharpsburg, Lee moved some of his men to advance positions. Hood established a line east of the Hagerstown Pike, with part of his troops in a cornfield and others extending the front to the East Woods. Skirmishers spread out far in front. Additional troops were rushed from reserve near Lee’s headquarters at the Oak Grove west of Sharpsburg; they extended the line west across the Hagerstown Pike. It was dusk by the time Hooker’s force was ready to charge. With Maj. Gen. George Meade’s men leading the way, they struck Hood’s Confederates at the edge of the East Woods and in the adjacent fields. A brisk artillery fire from opposing batteries forced the men to seek cover. The gathering darkness made it difficult for the forces on either side to locate their marks. Gradually the opening skirmish at Antietam ended. The thrust of the Federal skirmishers, however, made it clear to Lee just where the next Federal blow would fall. [Illustration: _Brig. Gen. John B. Hood._] [Illustration: _Maj. Gen. Joseph Hooker._ From photograph by Brady or assistant. Courtesy, Library of Congress.] Even as Hooker’s Federals withdrew to the cover of the North Woods, strong forces were moving to their aid—the two powerful corps under Mansfield and Sumner. Mansfield would lead the XII Corps across Antietam Creek about midnight and encamp 1½ miles northeast of Hooker. Sumner’s II Corps would cross the Antietam at Pry’s Mill Ford at 7:30 the next morning to lend additional support. Lee, too, was counting on reinforcements. McLaws’ division was expected to arrive on the field by midmorning. A. P. Hill, who had been left at Harpers Ferry to handle details of the surrender, would arrive late in the day. On the evening of September 16, picket lines were so close that the men on both sides, though unable to see each other, could hear footsteps. They knew that a tremendous struggle would begin at dawn. Some tried to sleep, but scattered firing throughout the night made this difficult. Others cleaned and cleaned again their rifled muskets, whose huge bullets made holes as big as silver dollars. Artillerists brought up ammunition for their smooth-bore Napoleons—so deadly at close range—and for the long-range rifled Parrott guns. And so these men got through the night, each one facing the impending crisis in his own way. [Illustration: _Union signal station on Elk Ridge. From here, McClellan’s observers spotted Confederate troop movements during the battle._ Courtesy, National Archives.] _Hooker Strikes at Daybreak_