As the battle escalated, Union Gen. Edwin Sumner moved the Second Corps across Antietam Creek and into the fighting, but the swift waters and difficult terrain separated his three divisions. One division advanced toward the West Woods while the other two fell behind and later assaulted the Sunken Road. At approximately 9:30 a.m., Sumner led Gen. John Sedgwick's division of more than 5,000 men forward with a plan to drive into the woods and sweep south against Lee's left flank. As the Union lines moved through the West Woods, Confederate artillery on Hauser Ridge opened fire, and within minutes bullets struck the Federals from three directions. Gen. Oliver Howard recalled that enemy artillery and infantry pursued and flanked the broken brigades with rapid, deadly volleys. Confederate reinforcements from the divisions of Gen. Lafayette McLaws and Gen. John Walker then struck the unsuspecting Union flank. After suffering more than 2,200 casualties in about twenty minutes, the Federals quickly withdrew from the West Woods.
