actually had. Zook's discovery was reported up to McClellan, but it was ignored, and Union troops that could have been used successfully elsewhere remained tied down. Fredericksburg Zook was forced to go on medical leave, probably due to chronic and disabling rheumatism, thus missing the Battle of Antietam. When he returned to the Army he was given command of French's brigade (3rd Brigade, 1st Division, II Corps) under division commander Maj. Gen. Winfield S. Hancock. The brigade was one of the first to arrive at Fredericksburg, Virginia, and he wanted to cross over the Rappahannock River as quickly as possible, before Confederate General Robert E. Lee could reinforce the town and the heights beyond it. However, Army of the Potomac commander Maj. Gen. Ambrose Burnside prevented the movement, wanting to wait for his army to concentrate and to receive pontoon bridges to make the river crossing. Zook wrote on December 10, "If we had had the pontoons promised when we arrived here we could have the hills on the other side of the river without cost over 50 men—now it will cost at least 10,000 if not more." While waiting for the pontoons to arrive, Zook served as military governor of Falmouth, Virginia. When the Battle of Fredericksburg began in earnest on December 13, French's division was the first to assault Marye's Heights. After being repulsed with heavy losses, Hancock's division moved forward with Zook's brigade in the lead. Zook had his horse shot out from under him and was momentarily stunned, but managed to lead his men to within 60 yards of the Stone Wall, one of the farthest Union advances of the battle. His brigade suffered 527 of the 12,000 Union casualties that night. General Hancock praised Zook's attack for its "spirit". Zook wrote afterward, "Now by God, if I don't get my star, I'm coming home." He was promoted to brigadier general in March 1863, to rank from November 29, 1862. After the battle, Zook briefly assumed command of the division while Hancock was absent on leave. Despite his successful promotion, however, the Battle of Fredericksburg affected him deeply: At the Battle of Chancellorsville in May 1863, Zook's brigade fought in the defensive line around the Chancellor Mansion, but facing east, where combat was lighter and his men suffered only 188 casualties. Disabled again by rheumatism, he left on medical leave to Washington, D.C., and rejoined his