 However , McClellan soon received a miraculous break of fortune . Union soldiers accidentally found a copy of Lee 's orders dividing his army , wrapped around a package of cigars in an abandoned camp . They delivered the order to McClellan 's headquarters in Frederick on September 13 . Upon realizing the intelligence value of this discovery , McClellan threw up his arms and exclaimed , " Now I know what to do ! " He waved the order at his old Army friend , Brig. Gen. John Gibbon , and said , " Here is a paper with which if I cannot whip Bobbie Lee , I will be willing to go home . " He telegraphed President Lincoln : " I have the whole rebel force in front of me , but I am confident , and no time shall be lost . I think Lee has made a gross mistake , and that he will be severely punished for it . I have all the plans of the rebels , and will catch them in their own trap if my men are equal to the emergency . ... Will send you trophies . " 
