Rubuta ci gaba ga wannan sakin layi - Lokacin da yakin basasa ya fara a 1861, Smith ya yi aiki a matsayin mai taimakawa ga sansanin Gwamna Richard Yates na Illinois. A ranar 26 ga Disamba, 1861 an nada shi a matsayin colonel na 45th Illinois Volunteer Infantry Regiment, tare da darajar da aka yi a ranar 23 ga Yuli, 1861 don maye gurbin tsohon Colonel wanda ya yi murabus daga kwamishinan jiharsa lokacin da rundunar ta shiga aikin tarayya. Ya jagoranci rundunarsa a yakin Fort Henry, Fort Donelson da Shiloh. A ranar 29 ga Nuwamba, 1862 an daukaka shi zuwa brigadier janar na Amurka Volunteers. Ya yi umurni na dan gajeren lokaci kafin ya dauki umurnin 8th Division, XVI Corps. Lokacin da Ulysses S. Grant ya fara yakin karshe da Vicksburg, an sanya Smith a matsayin kwamandan Brigade na 1, 3rd Division, XVII Corps. Ya yi yaƙi a yakin Port Gibson
, Raymond, Champion Hill da kuma a cikin hare-haren a kan Vicksburg. A watan Yuni, 1863 a tsakiyar kewaye da Vicksburg, an zabi Smith ne don maye gurbin Janar Isaac F. Quinby a matsayin kwamandan na 7th Division, XVII Corps bayan Quinby ya yi rashin lafiya kuma ya yi izini. A watan Satumba, 1863 an canja Smith zuwa umurnin 2nd Division, XVII Corps kuma an aika da sashinsa tare da William T. Sherman don taimakawa wajen taimakawa Chattanooga. A lokacin yakin Missionary Ridge, Smith ya shiga cikin hare-haren da aka yi a kan 'yancin' yancin 'yancin' yancin 'yancin' yancin 'yancin' yancin 'yancin' yancin 'yancin 'yancin' yancin 'yancin 'yancin' yancin 'yancin 'yancin' yancin 'yancin 'yancin 'yancin' yancin 'yancin 'yancin 'yancin' yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin' yancin 'yancin 'yancin 'yancin 'yancin' yancin 'yancin 'yancin 'yancin 'yancin 'yancin' yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin' yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin 'yancin