Tuhia he tohutoro mō tēnei wāhanga - I te pakarutanga o te Pakanga ā-Iwi i te tau 1861, ka wehe atu a von Vegesack ki Te Hononga o Amerika, a, ka uru atu ki te ope taua o te Kotahitanga. I riro ia hei rangatira mo te 58 o nga hoia o Ohio. I taua tau ano, i whakatairangahia ia hei rangatira i roto i nga kaimahi o te rangatira a John E. Wool. I te tuatahi i mahi ia ki Fort Monroe. Hei kaiawhina (ADC) ki a Joseph K. Mansfield i uru ia ki te pupuhi puhi o Newport News. I te tau 1862 ka whakarere ia, engari ka uru atu ia ki a Major General George B. McClellan i tana whakapae o Yorktown. Hei ADC ki Butterfield i uru ia ki nga pakanga o Hanover Court House, o Seven Pines me Fair Oaks. I whawhai ia ki Mechanicsville, Gaines's Mill, Savage's Station
, me Malvern Hill. I tohua a Vegesack hei koronel o te 20th New York Infantry, te roopu Tiamana "Turner". I whakawhiwhia ki a ia te whakahau mo te 3rd brigade i roto i te wehenga a General William Farrar Smith o te 6th Army Corps. I uru ia ki te Pakanga Tuarua o Bull Run. I riro i a ia ngā pukepuke i waho o Jefferson, Maryland. I whakakitea e ia he maia i Antietam. I whawhai a Vegesack i te Pakanga o Fredericksburg. I te marama o Mei 1863 ko te roopu o Vegesack tetahi waahanga o te parirau maui o Joseph Hooker i te Pakanga o Chancellorsville.