Hill's division had moved across Beaver Dam Creek early in the morning, finding the former Union line lightly defended. As they proceeded eastward and approached Gaines' Mill at about the time that D.H. Hill's men were engaged, Porter formally asked McClellan to send Slocum's division across the Chickahominy over Alexander's Bridge to support him. Hill directed the brigades of Maxcy Gregg and Lawrence O'Bryan Branch to spearhead the assault, as they had not been engaged at Beaver Dam Creek and were well-rested. Gregg was held up by skirmishers from Col. Hiram Berdan's 1st U.S. Sharpshooters and the 9th Massachusetts Infantry. By early afternoon, he had run into strong opposition by Porter, deployed along Boatswain's Creek, and the swampy terrain was a major obstacle against the advance. A particularly bloody engagement occurred as the 1st South Carolina Rifles attacked a Massachusetts battery, but were repulsed by Zouaves of the 5th New York, which inflicted 57% casualties (76 killed, 221 wounded, and 58 missing) on the South Carolinians, the greatest Confederate regimental losses of the day. Branch's brigade fared no better, losing 401 men in two hours of fighting. Following behind them, Joseph R. Anderson's brigade launched three assaults on the Union lines without putting a dent in them. Field's brigade became bogged down in the swamp, and some of the men in the rear ended up firing into their comrades. Some of Gregg's men reached the other side of the creek; none of the rest came close. Instead of pursuing a fleeing enemy, as his orders had directed, A.P. Hill attacked an entrenched Union position, losing about 2,000 of his 13,200 men in the failed attempt. Combined with his attacks at Mechanicsville the previous day, the Light Division had lost over a quarter of its men. General McClellan was encouraged by the telegrams Porter had sent back to his headquarters a few miles to the rear. He replied, "If the enemy are retiring and you are a chasseur, pitch in." He also told Franklin to cross the river over the Duane bridge and attack the enemy's flank if he saw a chance, but he was dismayed to hear that the VI Corps commander had destroyed the bridge for fear of a possible enemy attack. At the same time, Brig. Gen. Edwin V. Sumner of the II Corps reported enemy activity in his front. McClellan's optimism was dashed, and he ordered that