Ka kammala wannan magana: Da barkewar yakin basasa, Capehart ya bar aikin likitancinsa a Bridgeport kuma ya ba da kansa ga rundunar Union. An nada shi likitan likitancin na 1st West Virginia Cavalry a ranar 18 ga Satumba, 1861. A ƙarshen rabin 1863, ya shiga cikin yaƙe-yaƙe na Gettysburg, Bristoe Station, da
Ka yi gudu. Bisa ga shawarwarin Janar Judson Kilpatrick da sauransu, Capehart ya zama colonel kuma ya yi nasara da Nathaniel P. Richmond, wanda ya yi murabus saboda matsalolin kiwon lafiya, a matsayin kwamandan rundunar a ranar 22 ga Fabrairu, 1864.