 Ramba uchiverenga ndima iyi - Hondo yevagari vemo payakatanga, McCook akaunganidza boka ndokujoina uto rechi31 reIllinois Infantry, achishumira pasi peshamwari yake, Colonel John A. Logan. Akaona chiito muhondo dzeFort Henryuye Fort Donelson, uko akakuvadzwa zvakakomba. Akazopiwa basa rokutungamirira brigade yaLogan apo wokupedzisira akatora hurumende. Pakazosvika Campaign yeVicksburg, McCook akanga akwidziridzwa zvakare kuti atsive Logan semutungamiri weboka, achitungamirira panguva yeKukombwa kweVicksburg pasi paUlysses S. Grant. Muna 1864, akashanda achiremekedzwa muChattanooga neAtlanta mishandirapamwe uye muMarch to the Sea pasi paWilliam T. Sherman. Akakuvadzwa zvakakomba katatu asi akapona muhondo. 