Disappointed by McClellan's failure to destroy Lee's army, Lincoln named Ambrose Burnside as commander of the Army of the Potomac. Burnside ordered an attack across the Rappahannock River at Fredericksburg, Virginia. Delays in bridging the river allowed Lee's army ample time to organize strong defenses, and the Union frontal assault on December 13, 1862, was a disaster. There were 12,600 Union casualties to 5,000 Confederate; one of the most one-sided battles in the Civil War. After this victory, Lee reportedly said, "It is well that war is so terrible, else we should grow too fond of it." At Fredericksburg, according to historian Michael Fellman, Lee had completely entered into the "spirit of war, where destructiveness took on its own beauty."