At 4:30 a.m. on June 3, the three Union corps began to advance through a thick ground fog. Massive fire from the Confederate lines quickly caused heavy casualties, and the survivors were pinned down. The most effective performance of the day was on the Union left flank, where Hancock's corps was able to break through a portion of Breckinridge's front line and drive those defenders out of their entrenchments in hand-to-hand fighting. However, nearby Confederate artillery turned the entrenchments into a death trap for the Federals. Breckinridge's reserves counterattacked these men from the division of Brig. Gen. Francis C. Barlow and drove them off. Hancock's other advanced division, under Brig. Gen. John Gibbon, became disordered in swampy ground and could not advance through the heavy Confederate fire. One of Gibbon's men, complaining of a lack of reconnaissance, wrote, "We felt it was murder, not war, or at best a very serious mistake had been made."