Kammala wannan jumlar: A lokacin da yakin basasa ya barke a 1861, von Vegesack ya tafi Amurka kuma ya shiga rundunar Union. Ya zama kyaftin na 58th Ohio Infantry. A wannan shekarar, an daukaka shi zuwa Manjo a cikin ma'aikatan Janar John E. Wool. Da farko ya yi aiki a Fort Monroe. A matsayin mai taimakawa (ADC) ga Joseph K. Mansfield ya shiga cikin harin bam na Newport News. A shekara ta 1862 ya yi murabus, amma sai ya shiga Major General George B. McClellan a cikin kewaye da Yorktown. A matsayin ADC zuwa Butterfield ya shiga cikin yaƙe-yaƙe na Hanover Court House, na Bakwai Pines da Fair Oaks. Ya kasance a yakin Mechanicsville, Gaines Mill,
Tashar Savage, da kuma Malvern Hill. An nada Vegesack a matsayin colonel na 20th New York Infantry, na Jamus "Turner" regiment. An ba shi umurni a kan brigade na 3 a cikin Janar William Farrar Smith's division na 6th Army Corps. Ya shiga cikin Yaƙin Bull Run na biyu. Ya kama tuddai a wajen Jefferson, Maryland. Ya nuna jaruntaka a Antietam. Vegesack yana cikin yakin Fredericksburg. A watan Mayun 1863 Vegesack ta regiment wani bangare ne na Joseph Hooker ta hagu reshe a cikin Battle of Chancellorsville.