Wheeler fell seriously ill during the campaign and turned over command of the division to Brig. Gen. Samuel S. Sumner. Wheeler was still incapacitated in July when the Battle of San Juan Hill began but once he heard the sound of guns, the "War Child" returned to the front despite his illness. Being the senior officer present at the front he first issued orders to the 1st Division, under Jacob F. Kent, before returning to his own command. Upon taking the heights, Wheeler assured General William R. Shafter that the position could be held against a possible counterattack. He led the division through the Siege of Santiago and was a senior member of the peace commission.